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diff --git a/doc/gperf.html b/doc/gperf.html deleted file mode 100644 index bc964f9..0000000 --- a/doc/gperf.html +++ /dev/null @@ -1,2482 +0,0 @@ -<HTML> -<HEAD> -<!-- This HTML file has been created by texi2html 1.52b - from gperf.texi on 20 December 2009 --> - -<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=UTF-8"> -<TITLE>Perfect Hash Function Generator</TITLE> -</HEAD> -<BODY> -<H1>User's Guide to <CODE>gperf</CODE> 3.1</H1> -<H2>The GNU Perfect Hash Function Generator</H2> -<H2>Edition 3.1, 20 December 2009</H2> -<ADDRESS>Douglas C. Schmidt</ADDRESS> -<ADDRESS>Bruno Haible</ADDRESS> -<P> -<P><HR><P> -<H1>Table of Contents</H1> -<UL> -<LI><A NAME="TOC1" HREF="gperf.html#SEC1">GNU GENERAL PUBLIC LICENSE</A> -<LI><A NAME="TOC2" HREF="gperf.html#SEC2">Contributors to GNU <CODE>gperf</CODE> Utility</A> -<LI><A NAME="TOC3" HREF="gperf.html#SEC3">2 Introduction</A> -<LI><A NAME="TOC4" HREF="gperf.html#SEC4">3 Static search structures and GNU <CODE>gperf</CODE></A> -<LI><A NAME="TOC5" HREF="gperf.html#SEC5">4 High-Level Description of GNU <CODE>gperf</CODE></A> -<UL> -<LI><A NAME="TOC6" HREF="gperf.html#SEC6">4.1 Input Format to <CODE>gperf</CODE></A> -<UL> -<LI><A NAME="TOC7" HREF="gperf.html#SEC7">4.1.1 Declarations</A> -<UL> -<LI><A NAME="TOC8" HREF="gperf.html#SEC8">4.1.1.1 User-supplied <CODE>struct</CODE></A> -<LI><A NAME="TOC9" HREF="gperf.html#SEC9">4.1.1.2 Gperf Declarations</A> -<LI><A NAME="TOC10" HREF="gperf.html#SEC10">4.1.1.3 C Code Inclusion</A> -</UL> -<LI><A NAME="TOC11" HREF="gperf.html#SEC11">4.1.2 Format for Keyword Entries</A> -<LI><A NAME="TOC12" HREF="gperf.html#SEC12">4.1.3 Including Additional C Functions</A> -<LI><A NAME="TOC13" HREF="gperf.html#SEC13">4.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A> -</UL> -<LI><A NAME="TOC14" HREF="gperf.html#SEC14">4.2 Output Format for Generated C Code with <CODE>gperf</CODE></A> -<LI><A NAME="TOC15" HREF="gperf.html#SEC15">4.3 Use of NUL bytes</A> -<LI><A NAME="TOC16" HREF="gperf.html#SEC16">4.4 The Copyright of the Output</A> -</UL> -<LI><A NAME="TOC17" HREF="gperf.html#SEC17">5 Invoking <CODE>gperf</CODE></A> -<UL> -<LI><A NAME="TOC18" HREF="gperf.html#SEC18">5.1 Specifying the Location of the Output File</A> -<LI><A NAME="TOC19" HREF="gperf.html#SEC19">5.2 Options that affect Interpretation of the Input File</A> -<LI><A NAME="TOC20" HREF="gperf.html#SEC20">5.3 Options to specify the Language for the Output Code</A> -<LI><A NAME="TOC21" HREF="gperf.html#SEC21">5.4 Options for fine tuning Details in the Output Code</A> -<LI><A NAME="TOC22" HREF="gperf.html#SEC22">5.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A> -<LI><A NAME="TOC23" HREF="gperf.html#SEC23">5.6 Informative Output</A> -</UL> -<LI><A NAME="TOC24" HREF="gperf.html#SEC24">6 Known Bugs and Limitations with <CODE>gperf</CODE></A> -<LI><A NAME="TOC25" HREF="gperf.html#SEC25">7 Things Still Left to Do</A> -<LI><A NAME="TOC26" HREF="gperf.html#SEC26">8 Bibliography</A> -<LI><A NAME="TOC27" HREF="gperf.html#SEC27">Concept Index</A> -</UL> -<P><HR><P> - -<P> -Copyright (C) 1989-2009 Free Software Foundation, Inc. - -</P> - -<P> -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -</P> -<P> -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided also that the -section entitled “GNU General Public License” is included -exactly as in the original, and provided that the entire resulting -derived work is distributed under the terms of a permission notice -identical to this one. - -</P> -<P> -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that the section entitled “GNU General Public License” may be -included in a translation approved by the author instead of in the -original English. - -</P> - - - -<H1><A NAME="SEC1" HREF="gperf.html#TOC1">GNU GENERAL PUBLIC LICENSE</A></H1> -<P> -Version 3, 29 June 2007 - -</P> - - -<PRE> -Copyright (C) 2007 Free Software Foundation, Inc. <A HREF="http://fsf.org/">http://fsf.org/</A> - -Everyone is permitted to copy and distribute verbatim copies of this -license document, but changing it is not allowed. -</PRE> - - -<H2>1.0 Preamble</H2> - -<P> -The GNU General Public License is a free, copyleft license for -software and other kinds of works. - -</P> -<P> -The licenses for most software and other practical works are designed -to take away your freedom to share and change the works. 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It is safest -to attach them to the start of each source file to most effectively -state the exclusion of warranty; and each file should have at least -the “copyright” line and a pointer to where the full notice is found. - -</P> - -<PRE> -<VAR>one line to give the program's name and a brief idea of what it does.</VAR> -Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR> - -This program is free software: you can redistribute it and/or modify -it under the terms of the GNU General Public License as published by -the Free Software Foundation, either version 3 of the License, or (at -your option) any later version. - -This program is distributed in the hope that it will be useful, but -WITHOUT ANY WARRANTY; without even the implied warranty of -MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU -General Public License for more details. - -You should have received a copy of the GNU General Public License -along with this program. If not, see <A HREF="http://www.gnu.org/licenses/">http://www.gnu.org/licenses/</A>. -</PRE> - -<P> -Also add information on how to contact you by electronic and paper mail. - -</P> -<P> -If the program does terminal interaction, make it output a short -notice like this when it starts in an interactive mode: - -</P> - -<PRE> -<VAR>program</VAR> Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR> -This program comes with ABSOLUTELY NO WARRANTY; for details type <SAMP>‘show w’</SAMP>. -This is free software, and you are welcome to redistribute it -under certain conditions; type <SAMP>‘show c’</SAMP> for details. -</PRE> - -<P> -The hypothetical commands <SAMP>‘show w’</SAMP> and <SAMP>‘show c’</SAMP> should show -the appropriate parts of the General Public License. Of course, your -program's commands might be different; for a GUI interface, you would -use an “about box”. - -</P> -<P> -You should also get your employer (if you work as a programmer) or school, -if any, to sign a “copyright disclaimer” for the program, if necessary. -For more information on this, and how to apply and follow the GNU GPL, see -<A HREF="http://www.gnu.org/licenses/">http://www.gnu.org/licenses/</A>. - -</P> -<P> -The GNU General Public License does not permit incorporating your -program into proprietary programs. If your program is a subroutine -library, you may consider it more useful to permit linking proprietary -applications with the library. If this is what you want to do, use -the GNU Lesser General Public License instead of this License. But -first, please read <A HREF="http://www.gnu.org/philosophy/why-not-lgpl.html">http://www.gnu.org/philosophy/why-not-lgpl.html</A>. - -</P> - - -<H1><A NAME="SEC2" HREF="gperf.html#TOC2">Contributors to GNU <CODE>gperf</CODE> Utility</A></H1> - - -<UL> -<LI> - -<A NAME="IDX1"></A> -The GNU <CODE>gperf</CODE> perfect hash function generator utility was -written in GNU C++ by Douglas C. Schmidt. The general -idea for the perfect hash function generator was inspired by Keith -Bostic's algorithm written in C, and distributed to net.sources around -1984. The current program is a heavily modified, enhanced, and extended -implementation of Keith's basic idea, created at the University of -California, Irvine. Bugs, patches, and suggestions should be reported -to <CODE><bug-gnu-gperf@gnu.org></CODE>. - -<LI> - -Special thanks is extended to Michael Tiemann and Doug Lea, for -providing a useful compiler, and for giving me a forum to exhibit my -creation. - -In addition, Adam de Boor and Nels Olson provided many tips and insights -that greatly helped improve the quality and functionality of <CODE>gperf</CODE>. - -<LI> - -Bruno Haible enhanced and optimized the search algorithm. He also rewrote -the input routines and the output routines for better reliability, and -added a testsuite. -</UL> - - - -<H1><A NAME="SEC3" HREF="gperf.html#TOC3">2 Introduction</A></H1> - -<P> -<CODE>gperf</CODE> is a perfect hash function generator written in C++. It -transforms an <VAR>n</VAR> element user-specified keyword set <VAR>W</VAR> into a -perfect hash function <VAR>F</VAR>. <VAR>F</VAR> uniquely maps keywords in -<VAR>W</VAR> onto the range 0..<VAR>k</VAR>, where <VAR>k</VAR> >= <VAR>n-1</VAR>. If <VAR>k</VAR> -= <VAR>n-1</VAR> then <VAR>F</VAR> is a <EM>minimal</EM> perfect hash function. -<CODE>gperf</CODE> generates a 0..<VAR>k</VAR> element static lookup table and a -pair of C functions. These functions determine whether a given -character string <VAR>s</VAR> occurs in <VAR>W</VAR>, using at most one probe into -the lookup table. - -</P> -<P> -<CODE>gperf</CODE> currently generates the reserved keyword recognizer for -lexical analyzers in several production and research compilers and -language processing tools, including GNU C, GNU C++, GNU Java, GNU Pascal, -GNU Modula 3, and GNU indent. Complete C++ source code for <CODE>gperf</CODE> is -available from <CODE>http://ftp.gnu.org/pub/gnu/gperf/</CODE>. -A paper describing <CODE>gperf</CODE>'s design and implementation in greater -detail is available in the Second USENIX C++ Conference proceedings -or from <CODE>http://www.cs.wustl.edu/~schmidt/resume.html</CODE>. - -</P> - - -<H1><A NAME="SEC4" HREF="gperf.html#TOC4">3 Static search structures and GNU <CODE>gperf</CODE></A></H1> -<P> -<A NAME="IDX2"></A> - -</P> -<P> -A <EM>static search structure</EM> is an Abstract Data Type with certain -fundamental operations, e.g., <EM>initialize</EM>, <EM>insert</EM>, -and <EM>retrieve</EM>. Conceptually, all insertions occur before any -retrievals. In practice, <CODE>gperf</CODE> generates a <EM>static</EM> array -containing search set keywords and any associated attributes specified -by the user. Thus, there is essentially no execution-time cost for the -insertions. It is a useful data structure for representing <EM>static -search sets</EM>. Static search sets occur frequently in software system -applications. Typical static search sets include compiler reserved -words, assembler instruction opcodes, and built-in shell interpreter -commands. Search set members, called <EM>keywords</EM>, are inserted into -the structure only once, usually during program initialization, and are -not generally modified at run-time. - -</P> -<P> -Numerous static search structure implementations exist, e.g., -arrays, linked lists, binary search trees, digital search tries, and -hash tables. Different approaches offer trade-offs between space -utilization and search time efficiency. For example, an <VAR>n</VAR> element -sorted array is space efficient, though the average-case time -complexity for retrieval operations using binary search is -proportional to log <VAR>n</VAR>. Conversely, hash table implementations -often locate a table entry in constant time, but typically impose -additional memory overhead and exhibit poor worst case performance. - -</P> -<P> -<A NAME="IDX3"></A> -<EM>Minimal perfect hash functions</EM> provide an optimal solution for a -particular class of static search sets. A minimal perfect hash -function is defined by two properties: - -</P> - -<UL> -<LI> - -It allows keyword recognition in a static search set using at most -<EM>one</EM> probe into the hash table. This represents the “perfect” -property. -<LI> - -The actual memory allocated to store the keywords is precisely large -enough for the keyword set, and <EM>no larger</EM>. This is the -“minimal” property. -</UL> - -<P> -For most applications it is far easier to generate <EM>perfect</EM> hash -functions than <EM>minimal perfect</EM> hash functions. Moreover, -non-minimal perfect hash functions frequently execute faster than -minimal ones in practice. This phenomena occurs since searching a -sparse keyword table increases the probability of locating a “null” -entry, thereby reducing string comparisons. <CODE>gperf</CODE>'s default -behavior generates <EM>near-minimal</EM> perfect hash functions for -keyword sets. However, <CODE>gperf</CODE> provides many options that permit -user control over the degree of minimality and perfection. - -</P> -<P> -Static search sets often exhibit relative stability over time. For -example, Ada's 63 reserved words have remained constant for nearly a -decade. It is therefore frequently worthwhile to expend concerted -effort building an optimal search structure <EM>once</EM>, if it -subsequently receives heavy use multiple times. <CODE>gperf</CODE> removes -the drudgery associated with constructing time- and space-efficient -search structures by hand. It has proven a useful and practical tool -for serious programming projects. Output from <CODE>gperf</CODE> is currently -used in several production and research compilers, including GNU C, GNU -C++, GNU Java, GNU Pascal, and GNU Modula 3. The latter two compilers are -not yet part of the official GNU distribution. Each compiler utilizes -<CODE>gperf</CODE> to automatically generate static search structures that -efficiently identify their respective reserved keywords. - -</P> - - -<H1><A NAME="SEC5" HREF="gperf.html#TOC5">4 High-Level Description of GNU <CODE>gperf</CODE></A></H1> - -<P> -The perfect hash function generator <CODE>gperf</CODE> reads a set of -“keywords” from an input file (or from the standard input by -default). It attempts to derive a perfect hashing function that -recognizes a member of the <EM>static keyword set</EM> with at most a -single probe into the lookup table. If <CODE>gperf</CODE> succeeds in -generating such a function it produces a pair of C source code routines -that perform hashing and table lookup recognition. All generated C code -is directed to the standard output. Command-line options described -below allow you to modify the input and output format to <CODE>gperf</CODE>. - -</P> -<P> -By default, <CODE>gperf</CODE> attempts to produce time-efficient code, with -less emphasis on efficient space utilization. However, several options -exist that permit trading-off execution time for storage space and vice -versa. In particular, expanding the generated table size produces a -sparse search structure, generally yielding faster searches. -Conversely, you can direct <CODE>gperf</CODE> to utilize a C <CODE>switch</CODE> -statement scheme that minimizes data space storage size. Furthermore, -using a C <CODE>switch</CODE> may actually speed up the keyword retrieval time -somewhat. Actual results depend on your C compiler, of course. - -</P> -<P> -In general, <CODE>gperf</CODE> assigns values to the bytes it is using -for hashing until some set of values gives each keyword a unique value. -A helpful heuristic is that the larger the hash value range, the easier -it is for <CODE>gperf</CODE> to find and generate a perfect hash function. -Experimentation is the key to getting the most from <CODE>gperf</CODE>. - -</P> - - -<H2><A NAME="SEC6" HREF="gperf.html#TOC6">4.1 Input Format to <CODE>gperf</CODE></A></H2> -<P> -<A NAME="IDX4"></A> -<A NAME="IDX5"></A> -<A NAME="IDX6"></A> -<A NAME="IDX7"></A> -You can control the input file format by varying certain command-line -arguments, in particular the <SAMP>‘-t’</SAMP> option. The input's appearance -is similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE> (or UNIX -utilities <CODE>lex</CODE> and <CODE>yacc</CODE>). Here's an outline of the general -format: - -</P> - -<PRE> -declarations -%% -keywords -%% -functions -</PRE> - -<P> -<EM>Unlike</EM> <CODE>flex</CODE> or <CODE>bison</CODE>, the declarations section and -the functions section are optional. The following sections describe the -input format for each section. - -</P> - -<P> -It is possible to omit the declaration section entirely, if the <SAMP>‘-t’</SAMP> -option is not given. In this case the input file begins directly with the -first keyword line, e.g.: - -</P> - -<PRE> -january -february -march -april -... -</PRE> - - - -<H3><A NAME="SEC7" HREF="gperf.html#TOC7">4.1.1 Declarations</A></H3> - -<P> -The keyword input file optionally contains a section for including -arbitrary C declarations and definitions, <CODE>gperf</CODE> declarations that -act like command-line options, as well as for providing a user-supplied -<CODE>struct</CODE>. - -</P> - - - -<H4><A NAME="SEC8" HREF="gperf.html#TOC8">4.1.1.1 User-supplied <CODE>struct</CODE></A></H4> - -<P> -If the <SAMP>‘-t’</SAMP> option (or, equivalently, the <SAMP>‘%struct-type’</SAMP> declaration) -<EM>is</EM> enabled, you <EM>must</EM> provide a C <CODE>struct</CODE> as the last -component in the declaration section from the input file. The first -field in this struct must be of type <CODE>char *</CODE> or <CODE>const char *</CODE> -if the <SAMP>‘-P’</SAMP> option is not given, or of type <CODE>int</CODE> if the option -<SAMP>‘-P’</SAMP> (or, equivalently, the <SAMP>‘%pic’</SAMP> declaration) is enabled. -This first field must be called <SAMP>‘name’</SAMP>, although it is possible to modify -its name with the <SAMP>‘-K’</SAMP> option (or, equivalently, the -<SAMP>‘%define slot-name’</SAMP> declaration) described below. - -</P> -<P> -Here is a simple example, using months of the year and their attributes as -input: - -</P> - -<PRE> -struct month { char *name; int number; int days; int leap_days; }; -%% -january, 1, 31, 31 -february, 2, 28, 29 -march, 3, 31, 31 -april, 4, 30, 30 -may, 5, 31, 31 -june, 6, 30, 30 -july, 7, 31, 31 -august, 8, 31, 31 -september, 9, 30, 30 -october, 10, 31, 31 -november, 11, 30, 30 -december, 12, 31, 31 -</PRE> - -<P> -<A NAME="IDX8"></A> -Separating the <CODE>struct</CODE> declaration from the list of keywords and -other fields are a pair of consecutive percent signs, <SAMP>‘%%’</SAMP>, -appearing left justified in the first column, as in the UNIX utility -<CODE>lex</CODE>. - -</P> -<P> -If the <CODE>struct</CODE> has already been declared in an include file, it can -be mentioned in an abbreviated form, like this: - -</P> - -<PRE> -struct month; -%% -january, 1, 31, 31 -... -</PRE> - - - -<H4><A NAME="SEC9" HREF="gperf.html#TOC9">4.1.1.2 Gperf Declarations</A></H4> - -<P> -The declaration section can contain <CODE>gperf</CODE> declarations. They -influence the way <CODE>gperf</CODE> works, like command line options do. -In fact, every such declaration is equivalent to a command line option. -There are three forms of declarations: - -</P> - -<OL> -<LI> - -Declarations without argument, like <SAMP>‘%compare-lengths’</SAMP>. - -<LI> - -Declarations with an argument, like <SAMP>‘%switch=<VAR>count</VAR>’</SAMP>. - -<LI> - -Declarations of names of entities in the output file, like -<SAMP>‘%define lookup-function-name <VAR>name</VAR>’</SAMP>. -</OL> - -<P> -When a declaration is given both in the input file and as a command line -option, the command-line option's value prevails. - -</P> -<P> -The following <CODE>gperf</CODE> declarations are available. - -</P> -<DL COMPACT> - -<DT><SAMP>‘%delimiters=<VAR>delimiter-list</VAR>’</SAMP> -<DD> -<A NAME="IDX9"></A> -Allows you to provide a string containing delimiters used to -separate keywords from their attributes. The default is ",". This -option is essential if you want to use keywords that have embedded -commas or newlines. - -<DT><SAMP>‘%struct-type’</SAMP> -<DD> -<A NAME="IDX10"></A> -Allows you to include a <CODE>struct</CODE> type declaration for generated -code; see above for an example. - -<DT><SAMP>‘%ignore-case’</SAMP> -<DD> -<A NAME="IDX11"></A> -Consider upper and lower case ASCII characters as equivalent. The string -comparison will use a case insignificant character comparison. Note that -locale dependent case mappings are ignored. - -<DT><SAMP>‘%language=<VAR>language-name</VAR>’</SAMP> -<DD> -<A NAME="IDX12"></A> -Instructs <CODE>gperf</CODE> to generate code in the language specified by the -option's argument. Languages handled are currently: - -<DL COMPACT> - -<DT><SAMP>‘KR-C’</SAMP> -<DD> -Old-style K&R C. This language is understood by old-style C compilers and -ANSI C compilers, but ANSI C compilers may flag warnings (or even errors) -because of lacking <SAMP>‘const’</SAMP>. - -<DT><SAMP>‘C’</SAMP> -<DD> -Common C. This language is understood by ANSI C compilers, and also by -old-style C compilers, provided that you <CODE>#define const</CODE> to empty -for compilers which don't know about this keyword. - -<DT><SAMP>‘ANSI-C’</SAMP> -<DD> -ANSI C. This language is understood by ANSI C (C89, ISO C90) compilers, -ISO C99 compilers, and C++ compilers. - -<DT><SAMP>‘C++’</SAMP> -<DD> -C++. This language is understood by C++ compilers. -</DL> - -The default is ANSI-C. - -<DT><SAMP>‘%define slot-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX13"></A> -This declaration is only useful when option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) has been given. -By default, the program assumes the structure component identifier for -the keyword is <SAMP>‘name’</SAMP>. This option allows an arbitrary choice of -identifier for this component, although it still must occur as the first -field in your supplied <CODE>struct</CODE>. - -<DT><SAMP>‘%define initializer-suffix <VAR>initializers</VAR>’</SAMP> -<DD> -<A NAME="IDX14"></A> -This declaration is only useful when option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) has been given. -It permits to specify initializers for the structure members following -<VAR>slot-name</VAR> in empty hash table entries. The list of initializers -should start with a comma. By default, the emitted code will -zero-initialize structure members following <VAR>slot-name</VAR>. - -<DT><SAMP>‘%define hash-function-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX15"></A> -Allows you to specify the name for the generated hash function. Default -name is <SAMP>‘hash’</SAMP>. This option permits the use of two hash tables in -the same file. - -<DT><SAMP>‘%define lookup-function-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX16"></A> -Allows you to specify the name for the generated lookup function. -Default name is <SAMP>‘in_word_set’</SAMP>. This option permits multiple -generated hash functions to be used in the same application. - -<DT><SAMP>‘%define class-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX17"></A> -This option is only useful when option <SAMP>‘-L C++’</SAMP> (or, equivalently, -the <SAMP>‘%language=C++’</SAMP> declaration) has been given. It -allows you to specify the name of generated C++ class. Default name is -<CODE>Perfect_Hash</CODE>. - -<DT><SAMP>‘%7bit’</SAMP> -<DD> -<A NAME="IDX18"></A> -This option specifies that all strings that will be passed as arguments -to the generated hash function and the generated lookup function will -solely consist of 7-bit ASCII characters (bytes in the range 0..127). -(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do -<EM>not</EM> guarantee that a byte is in this range. Only an explicit -test like <SAMP>‘c >= 'A' && c <= 'Z'’</SAMP> guarantees this.) - -<DT><SAMP>‘%compare-lengths’</SAMP> -<DD> -<A NAME="IDX19"></A> -Compare keyword lengths before trying a string comparison. This option -is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC15">4.3 Use of NUL bytes</A>). It also might -cut down on the number of string comparisons made during the lookup, since -keywords with different lengths are never compared via <CODE>strcmp</CODE>. -However, using <SAMP>‘%compare-lengths’</SAMP> might greatly increase the size of the -generated C code if the lookup table range is large (which implies that -the switch option <SAMP>‘-S’</SAMP> or <SAMP>‘%switch’</SAMP> is not enabled), since the length -table contains as many elements as there are entries in the lookup table. - -<DT><SAMP>‘%compare-strncmp’</SAMP> -<DD> -<A NAME="IDX20"></A> -Generates C code that uses the <CODE>strncmp</CODE> function to perform -string comparisons. The default action is to use <CODE>strcmp</CODE>. - -<DT><SAMP>‘%readonly-tables’</SAMP> -<DD> -<A NAME="IDX21"></A> -Makes the contents of all generated lookup tables constant, i.e., -“readonly”. Many compilers can generate more efficient code for this -by putting the tables in readonly memory. - -<DT><SAMP>‘%enum’</SAMP> -<DD> -<A NAME="IDX22"></A> -Define constant values using an enum local to the lookup function rather -than with #defines. This also means that different lookup functions can -reside in the same file. Thanks to James Clark <CODE><jjc@ai.mit.edu></CODE>. - -<DT><SAMP>‘%includes’</SAMP> -<DD> -<A NAME="IDX23"></A> -Include the necessary system include file, <CODE><string.h></CODE>, at the -beginning of the code. By default, this is not done; the user must -include this header file himself to allow compilation of the code. - -<DT><SAMP>‘%global-table’</SAMP> -<DD> -<A NAME="IDX24"></A> -Generate the static table of keywords as a static global variable, -rather than hiding it inside of the lookup function (which is the -default behavior). - -<DT><SAMP>‘%pic’</SAMP> -<DD> -<A NAME="IDX25"></A> -Optimize the generated table for inclusion in shared libraries. This -reduces the startup time of programs using a shared library containing -the generated code. If the <SAMP>‘%struct-type’</SAMP> declaration (or, -equivalently, the option <SAMP>‘-t’</SAMP>) is also given, the first field of the -user-defined struct must be of type <SAMP>‘int’</SAMP>, not <SAMP>‘char *’</SAMP>, because -it will contain offsets into the string pool instead of actual strings. -To convert such an offset to a string, you can use the expression -<SAMP>‘stringpool + <VAR>o</VAR>’</SAMP>, where <VAR>o</VAR> is the offset. The string pool -name can be changed through the <SAMP>‘%define string-pool-name’</SAMP> declaration. - -<DT><SAMP>‘%define string-pool-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX26"></A> -Allows you to specify the name of the generated string pool created by -the declaration <SAMP>‘%pic’</SAMP> (or, equivalently, the option <SAMP>‘-P’</SAMP>). -The default name is <SAMP>‘stringpool’</SAMP>. This declaration permits the use of -two hash tables in the same file, with <SAMP>‘%pic’</SAMP> and even when the -<SAMP>‘%global-table’</SAMP> declaration (or, equivalently, the option <SAMP>‘-G’</SAMP>) -is given. - -<DT><SAMP>‘%null-strings’</SAMP> -<DD> -<A NAME="IDX27"></A> -Use NULL strings instead of empty strings for empty keyword table entries. -This reduces the startup time of programs using a shared library containing -the generated code (but not as much as the declaration <SAMP>‘%pic’</SAMP>), at the -expense of one more test-and-branch instruction at run time. - -<DT><SAMP>‘%define word-array-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX28"></A> -Allows you to specify the name for the generated array containing the -hash table. Default name is <SAMP>‘wordlist’</SAMP>. This option permits the -use of two hash tables in the same file, even when the option <SAMP>‘-G’</SAMP> -(or, equivalently, the <SAMP>‘%global-table’</SAMP> declaration) is given. - -<DT><SAMP>‘%define length-table-name <VAR>name</VAR>’</SAMP> -<DD> -<A NAME="IDX29"></A> -Allows you to specify the name for the generated array containing the -length table. Default name is <SAMP>‘lengthtable’</SAMP>. This option permits the -use of two length tables in the same file, even when the option <SAMP>‘-G’</SAMP> -(or, equivalently, the <SAMP>‘%global-table’</SAMP> declaration) is given. - -<DT><SAMP>‘%switch=<VAR>count</VAR>’</SAMP> -<DD> -<A NAME="IDX30"></A> -Causes the generated C code to use a <CODE>switch</CODE> statement scheme, -rather than an array lookup table. This can lead to a reduction in both -time and space requirements for some input files. The argument to this -option determines how many <CODE>switch</CODE> statements are generated. A -value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a -value of 2 generates 2 tables with 1/2 the elements in each -<CODE>switch</CODE>, etc. This is useful since many C compilers cannot -correctly generate code for large <CODE>switch</CODE> statements. This option -was inspired in part by Keith Bostic's original C program. - -<DT><SAMP>‘%omit-struct-type’</SAMP> -<DD> -<A NAME="IDX31"></A> -Prevents the transfer of the type declaration to the output file. Use -this option if the type is already defined elsewhere. -</DL> - - - -<H4><A NAME="SEC10" HREF="gperf.html#TOC10">4.1.1.3 C Code Inclusion</A></H4> - -<P> -<A NAME="IDX32"></A> -<A NAME="IDX33"></A> -Using a syntax similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE>, it -is possible to directly include C source text and comments verbatim into -the generated output file. This is accomplished by enclosing the region -inside left-justified surrounding <SAMP>‘%{’</SAMP>, <SAMP>‘%}’</SAMP> pairs. Here is -an input fragment based on the previous example that illustrates this -feature: - -</P> - -<PRE> -%{ -#include <assert.h> -/* This section of code is inserted directly into the output. */ -int return_month_days (struct month *months, int is_leap_year); -%} -struct month { char *name; int number; int days; int leap_days; }; -%% -january, 1, 31, 31 -february, 2, 28, 29 -march, 3, 31, 31 -... -</PRE> - - - -<H3><A NAME="SEC11" HREF="gperf.html#TOC11">4.1.2 Format for Keyword Entries</A></H3> - -<P> -The second input file format section contains lines of keywords and any -associated attributes you might supply. A line beginning with <SAMP>‘#’</SAMP> -in the first column is considered a comment. Everything following the -<SAMP>‘#’</SAMP> is ignored, up to and including the following newline. A line -beginning with <SAMP>‘%’</SAMP> in the first column is an option declaration and -must not occur within the keywords section. - -</P> -<P> -The first field of each non-comment line is always the keyword itself. It -can be given in two ways: as a simple name, i.e., without surrounding -string quotation marks, or as a string enclosed in double-quotes, in -C syntax, possibly with backslash escapes like <CODE>\"</CODE> or <CODE>\234</CODE> -or <CODE>\xa8</CODE>. In either case, it must start right at the beginning -of the line, without leading whitespace. -In this context, a “field” is considered to extend up to, but -not include, the first blank, comma, or newline. Here is a simple -example taken from a partial list of C reserved words: - -</P> - -<PRE> -# These are a few C reserved words, see the c.gperf file -# for a complete list of ANSI C reserved words. -unsigned -sizeof -switch -signed -if -default -for -while -return -</PRE> - -<P> -Note that unlike <CODE>flex</CODE> or <CODE>bison</CODE> the first <SAMP>‘%%’</SAMP> marker -may be elided if the declaration section is empty. - -</P> -<P> -Additional fields may optionally follow the leading keyword. Fields -should be separated by commas, and terminate at the end of line. What -these fields mean is entirely up to you; they are used to initialize the -elements of the user-defined <CODE>struct</CODE> provided by you in the -declaration section. If the <SAMP>‘-t’</SAMP> option (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) is <EM>not</EM> enabled -these fields are simply ignored. All previous examples except the last -one contain keyword attributes. - -</P> - - -<H3><A NAME="SEC12" HREF="gperf.html#TOC12">4.1.3 Including Additional C Functions</A></H3> - -<P> -The optional third section also corresponds closely with conventions -found in <CODE>flex</CODE> and <CODE>bison</CODE>. All text in this section, -starting at the final <SAMP>‘%%’</SAMP> and extending to the end of the input -file, is included verbatim into the generated output file. Naturally, -it is your responsibility to ensure that the code contained in this -section is valid C. - -</P> - - -<H3><A NAME="SEC13" HREF="gperf.html#TOC13">4.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A></H3> - -<P> -If you want to invoke GNU <CODE>indent</CODE> on a <CODE>gperf</CODE> input file, -you will see that GNU <CODE>indent</CODE> doesn't understand the <SAMP>‘%%’</SAMP>, -<SAMP>‘%{’</SAMP> and <SAMP>‘%}’</SAMP> directives that control <CODE>gperf</CODE>'s -interpretation of the input file. Therefore you have to insert some -directives for GNU <CODE>indent</CODE>. More precisely, assuming the most -general input file structure - -</P> - -<PRE> -declarations part 1 -%{ -verbatim code -%} -declarations part 2 -%% -keywords -%% -functions -</PRE> - -<P> -you would insert <SAMP>‘*INDENT-OFF*’</SAMP> and <SAMP>‘*INDENT-ON*’</SAMP> comments -as follows: - -</P> - -<PRE> -/* *INDENT-OFF* */ -declarations part 1 -%{ -/* *INDENT-ON* */ -verbatim code -/* *INDENT-OFF* */ -%} -declarations part 2 -%% -keywords -%% -/* *INDENT-ON* */ -functions -</PRE> - - - -<H2><A NAME="SEC14" HREF="gperf.html#TOC14">4.2 Output Format for Generated C Code with <CODE>gperf</CODE></A></H2> -<P> -<A NAME="IDX34"></A> - -</P> -<P> -Several options control how the generated C code appears on the standard -output. Two C functions are generated. They are called <CODE>hash</CODE> and -<CODE>in_word_set</CODE>, although you may modify their names with a command-line -option. Both functions require two arguments, a string, <CODE>char *</CODE> -<VAR>str</VAR>, and a length parameter, <CODE>int</CODE> <VAR>len</VAR>. Their default -function prototypes are as follows: - -</P> -<P> -<DL> -<DT><U>Function:</U> unsigned int <B>hash</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I> -<DD><A NAME="IDX35"></A> -By default, the generated <CODE>hash</CODE> function returns an integer value -created by adding <VAR>len</VAR> to several user-specified <VAR>str</VAR> byte -positions indexed into an <EM>associated values</EM> table stored in a -local static array. The associated values table is constructed -internally by <CODE>gperf</CODE> and later output as a static local C array -called <SAMP>‘hash_table’</SAMP>. The relevant selected positions (i.e. indices -into <VAR>str</VAR>) are specified via the <SAMP>‘-k’</SAMP> option when running -<CODE>gperf</CODE>, as detailed in the <EM>Options</EM> section below (see section <A HREF="gperf.html#SEC17">5 Invoking <CODE>gperf</CODE></A>). -</DL> - -</P> -<P> -<DL> -<DT><U>Function:</U> <B>in_word_set</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I> -<DD><A NAME="IDX36"></A> -If <VAR>str</VAR> is in the keyword set, returns a pointer to that -keyword. More exactly, if the option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) was given, it returns -a pointer to the matching keyword's structure. Otherwise it returns -<CODE>NULL</CODE>. -</DL> - -</P> -<P> -If the option <SAMP>‘-c’</SAMP> (or, equivalently, the <SAMP>‘%compare-strncmp’</SAMP> -declaration) is not used, <VAR>str</VAR> must be a NUL terminated -string of exactly length <VAR>len</VAR>. If <SAMP>‘-c’</SAMP> (or, equivalently, the -<SAMP>‘%compare-strncmp’</SAMP> declaration) is used, <VAR>str</VAR> must -simply be an array of <VAR>len</VAR> bytes and does not need to be NUL -terminated. - -</P> -<P> -The code generated for these two functions is affected by the following -options: - -</P> -<DL COMPACT> - -<DT><SAMP>‘-t’</SAMP> -<DD> -<DT><SAMP>‘--struct-type’</SAMP> -<DD> -Make use of the user-defined <CODE>struct</CODE>. - -<DT><SAMP>‘-S <VAR>total-switch-statements</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--switch=<VAR>total-switch-statements</VAR>’</SAMP> -<DD> -<A NAME="IDX37"></A> -Generate 1 or more C <CODE>switch</CODE> statement rather than use a large, -(and potentially sparse) static array. Although the exact time and -space savings of this approach vary according to your C compiler's -degree of optimization, this method often results in smaller and faster -code. -</DL> - -<P> -If the <SAMP>‘-t’</SAMP> and <SAMP>‘-S’</SAMP> options (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> and <SAMP>‘%switch’</SAMP> declarations) are omitted, the default -action -is to generate a <CODE>char *</CODE> array containing the keywords, together with -additional empty strings used for padding the array. By experimenting -with the various input and output options, and timing the resulting C -code, you can determine the best option choices for different keyword -set characteristics. - -</P> - - -<H2><A NAME="SEC15" HREF="gperf.html#TOC15">4.3 Use of NUL bytes</A></H2> -<P> -<A NAME="IDX38"></A> - -</P> -<P> -By default, the code generated by <CODE>gperf</CODE> operates on zero -terminated strings, the usual representation of strings in C. This means -that the keywords in the input file must not contain NUL bytes, -and the <VAR>str</VAR> argument passed to <CODE>hash</CODE> or <CODE>in_word_set</CODE> -must be NUL terminated and have exactly length <VAR>len</VAR>. - -</P> -<P> -If option <SAMP>‘-c’</SAMP> (or, equivalently, the <SAMP>‘%compare-strncmp’</SAMP> -declaration) is used, then the <VAR>str</VAR> argument does not need -to be NUL terminated. The code generated by <CODE>gperf</CODE> will only -access the first <VAR>len</VAR>, not <VAR>len+1</VAR>, bytes starting at <VAR>str</VAR>. -However, the keywords in the input file still must not contain NUL -bytes. - -</P> -<P> -If option <SAMP>‘-l’</SAMP> (or, equivalently, the <SAMP>‘%compare-lengths’</SAMP> -declaration) is used, then the hash table performs binary -comparison. The keywords in the input file may contain NUL bytes, -written in string syntax as <CODE>\000</CODE> or <CODE>\x00</CODE>, and the code -generated by <CODE>gperf</CODE> will treat NUL like any other byte. -Also, in this case the <SAMP>‘-c’</SAMP> option (or, equivalently, the -<SAMP>‘%compare-strncmp’</SAMP> declaration) is ignored. - -</P> - - -<H2><A NAME="SEC16" HREF="gperf.html#TOC16">4.4 The Copyright of the Output</A></H2> -<P> -<A NAME="IDX39"></A> - -</P> -<P> -<CODE>gperf</CODE> is under GPL, but that does not cause the output produced -by <CODE>gperf</CODE> to be under GPL. The reason is that the output contains -only small pieces of text that come directly from <CODE>gperf</CODE>'s source -code -- only about 7 lines long, too small for being significant --, and -therefore the output is not a “work based on <CODE>gperf</CODE>” (in the -sense of the GPL version 3). - -</P> -<P> -On the other hand, the output produced by <CODE>gperf</CODE> contains -essentially all of the input file. Therefore the output is a -“derivative work” of the input (in the sense of U.S. copyright law); -and its copyright status depends on the copyright of the input. For most -software licenses, the result is that the the output is under the same -license, with the same copyright holder, as the input that was passed to -<CODE>gperf</CODE>. - -</P> - - -<H1><A NAME="SEC17" HREF="gperf.html#TOC17">5 Invoking <CODE>gperf</CODE></A></H1> - -<P> -There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make -the program more convenient for use with real applications. “On-line” -help is readily available via the <SAMP>‘--help’</SAMP> option. Here is the -complete list of options. - -</P> - - - -<H2><A NAME="SEC18" HREF="gperf.html#TOC18">5.1 Specifying the Location of the Output File</A></H2> - -<DL COMPACT> - -<DT><SAMP>‘--output-file=<VAR>file</VAR>’</SAMP> -<DD> -Allows you to specify the name of the file to which the output is written to. -</DL> - -<P> -The results are written to standard output if no output file is specified -or if it is <SAMP>‘-’</SAMP>. - -</P> - - -<H2><A NAME="SEC19" HREF="gperf.html#TOC19">5.2 Options that affect Interpretation of the Input File</A></H2> - -<P> -These options are also available as declarations in the input file -(see section <A HREF="gperf.html#SEC9">4.1.1.2 Gperf Declarations</A>). - -</P> -<DL COMPACT> - -<DT><SAMP>‘-e <VAR>keyword-delimiter-list</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--delimiters=<VAR>keyword-delimiter-list</VAR>’</SAMP> -<DD> -<A NAME="IDX40"></A> -Allows you to provide a string containing delimiters used to -separate keywords from their attributes. The default is ",". This -option is essential if you want to use keywords that have embedded -commas or newlines. One useful trick is to use -e'TAB', where TAB is -the literal tab character. - -<DT><SAMP>‘-t’</SAMP> -<DD> -<DT><SAMP>‘--struct-type’</SAMP> -<DD> -Allows you to include a <CODE>struct</CODE> type declaration for generated -code. Any text before a pair of consecutive <SAMP>‘%%’</SAMP> is considered -part of the type declaration. Keywords and additional fields may follow -this, one group of fields per line. A set of examples for generating -perfect hash tables and functions for Ada, C, C++, Pascal, Modula 2, -Modula 3 and JavaScript reserved words are distributed with this release. - -<DT><SAMP>‘--ignore-case’</SAMP> -<DD> -Consider upper and lower case ASCII characters as equivalent. The string -comparison will use a case insignificant character comparison. Note that -locale dependent case mappings are ignored. This option is therefore not -suitable if a properly internationalized or locale aware case mapping -should be used. (For example, in a Turkish locale, the upper case equivalent -of the lowercase ASCII letter <SAMP>‘i’</SAMP> is the non-ASCII character -<SAMP>‘capital i with dot above’</SAMP>.) For this case, it is better to apply -an uppercase or lowercase conversion on the string before passing it to -the <CODE>gperf</CODE> generated function. -</DL> - - - -<H2><A NAME="SEC20" HREF="gperf.html#TOC20">5.3 Options to specify the Language for the Output Code</A></H2> - -<P> -These options are also available as declarations in the input file -(see section <A HREF="gperf.html#SEC9">4.1.1.2 Gperf Declarations</A>). - -</P> -<DL COMPACT> - -<DT><SAMP>‘-L <VAR>generated-language-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--language=<VAR>generated-language-name</VAR>’</SAMP> -<DD> -Instructs <CODE>gperf</CODE> to generate code in the language specified by the -option's argument. Languages handled are currently: - -<DL COMPACT> - -<DT><SAMP>‘KR-C’</SAMP> -<DD> -Old-style K&R C. This language is understood by old-style C compilers and -ANSI C compilers, but ANSI C compilers may flag warnings (or even errors) -because of lacking <SAMP>‘const’</SAMP>. - -<DT><SAMP>‘C’</SAMP> -<DD> -Common C. This language is understood by ANSI C compilers, and also by -old-style C compilers, provided that you <CODE>#define const</CODE> to empty -for compilers which don't know about this keyword. - -<DT><SAMP>‘ANSI-C’</SAMP> -<DD> -ANSI C. This language is understood by ANSI C compilers and C++ compilers. - -<DT><SAMP>‘C++’</SAMP> -<DD> -C++. This language is understood by C++ compilers. -</DL> - -The default is ANSI-C. - -<DT><SAMP>‘-a’</SAMP> -<DD> -This option is supported for compatibility with previous releases of -<CODE>gperf</CODE>. It does not do anything. - -<DT><SAMP>‘-g’</SAMP> -<DD> -This option is supported for compatibility with previous releases of -<CODE>gperf</CODE>. It does not do anything. -</DL> - - - -<H2><A NAME="SEC21" HREF="gperf.html#TOC21">5.4 Options for fine tuning Details in the Output Code</A></H2> - -<P> -Most of these options are also available as declarations in the input file -(see section <A HREF="gperf.html#SEC9">4.1.1.2 Gperf Declarations</A>). - -</P> -<DL COMPACT> - -<DT><SAMP>‘-K <VAR>slot-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--slot-name=<VAR>slot-name</VAR>’</SAMP> -<DD> -<A NAME="IDX41"></A> -This option is only useful when option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) has been given. -By default, the program assumes the structure component identifier for -the keyword is <SAMP>‘name’</SAMP>. This option allows an arbitrary choice of -identifier for this component, although it still must occur as the first -field in your supplied <CODE>struct</CODE>. - -<DT><SAMP>‘-F <VAR>initializers</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--initializer-suffix=<VAR>initializers</VAR>’</SAMP> -<DD> -<A NAME="IDX42"></A> -This option is only useful when option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) has been given. -It permits to specify initializers for the structure members following -<VAR>slot-name</VAR> in empty hash table entries. The list of initializers -should start with a comma. By default, the emitted code will -zero-initialize structure members following <VAR>slot-name</VAR>. - -<DT><SAMP>‘-H <VAR>hash-function-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--hash-function-name=<VAR>hash-function-name</VAR>’</SAMP> -<DD> -Allows you to specify the name for the generated hash function. Default -name is <SAMP>‘hash’</SAMP>. This option permits the use of two hash tables in -the same file. - -<DT><SAMP>‘-N <VAR>lookup-function-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--lookup-function-name=<VAR>lookup-function-name</VAR>’</SAMP> -<DD> -Allows you to specify the name for the generated lookup function. -Default name is <SAMP>‘in_word_set’</SAMP>. This option permits multiple -generated hash functions to be used in the same application. - -<DT><SAMP>‘-Z <VAR>class-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--class-name=<VAR>class-name</VAR>’</SAMP> -<DD> -<A NAME="IDX43"></A> -This option is only useful when option <SAMP>‘-L C++’</SAMP> (or, equivalently, -the <SAMP>‘%language=C++’</SAMP> declaration) has been given. It -allows you to specify the name of generated C++ class. Default name is -<CODE>Perfect_Hash</CODE>. - -<DT><SAMP>‘-7’</SAMP> -<DD> -<DT><SAMP>‘--seven-bit’</SAMP> -<DD> -This option specifies that all strings that will be passed as arguments -to the generated hash function and the generated lookup function will -solely consist of 7-bit ASCII characters (bytes in the range 0..127). -(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do -<EM>not</EM> guarantee that a byte is in this range. Only an explicit -test like <SAMP>‘c >= 'A' && c <= 'Z'’</SAMP> guarantees this.) This was the -default in versions of <CODE>gperf</CODE> earlier than 2.7; now the default is -to support 8-bit and multibyte characters. - -<DT><SAMP>‘-l’</SAMP> -<DD> -<DT><SAMP>‘--compare-lengths’</SAMP> -<DD> -Compare keyword lengths before trying a string comparison. This option -is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC15">4.3 Use of NUL bytes</A>). It also might -cut down on the number of string comparisons made during the lookup, since -keywords with different lengths are never compared via <CODE>strcmp</CODE>. -However, using <SAMP>‘-l’</SAMP> might greatly increase the size of the -generated C code if the lookup table range is large (which implies that -the switch option <SAMP>‘-S’</SAMP> or <SAMP>‘%switch’</SAMP> is not enabled), since the length -table contains as many elements as there are entries in the lookup table. - -<DT><SAMP>‘-c’</SAMP> -<DD> -<DT><SAMP>‘--compare-strncmp’</SAMP> -<DD> -Generates C code that uses the <CODE>strncmp</CODE> function to perform -string comparisons. The default action is to use <CODE>strcmp</CODE>. - -<DT><SAMP>‘-C’</SAMP> -<DD> -<DT><SAMP>‘--readonly-tables’</SAMP> -<DD> -Makes the contents of all generated lookup tables constant, i.e., -“readonly”. Many compilers can generate more efficient code for this -by putting the tables in readonly memory. - -<DT><SAMP>‘-E’</SAMP> -<DD> -<DT><SAMP>‘--enum’</SAMP> -<DD> -Define constant values using an enum local to the lookup function rather -than with #defines. This also means that different lookup functions can -reside in the same file. Thanks to James Clark <CODE><jjc@ai.mit.edu></CODE>. - -<DT><SAMP>‘-I’</SAMP> -<DD> -<DT><SAMP>‘--includes’</SAMP> -<DD> -Include the necessary system include file, <CODE><string.h></CODE>, at the -beginning of the code. By default, this is not done; the user must -include this header file himself to allow compilation of the code. - -<DT><SAMP>‘-G’</SAMP> -<DD> -<DT><SAMP>‘--global-table’</SAMP> -<DD> -Generate the static table of keywords as a static global variable, -rather than hiding it inside of the lookup function (which is the -default behavior). - -<DT><SAMP>‘-P’</SAMP> -<DD> -<DT><SAMP>‘--pic’</SAMP> -<DD> -Optimize the generated table for inclusion in shared libraries. This -reduces the startup time of programs using a shared library containing -the generated code. If the option <SAMP>‘-t’</SAMP> (or, equivalently, the -<SAMP>‘%struct-type’</SAMP> declaration) is also given, the first field of the -user-defined struct must be of type <SAMP>‘int’</SAMP>, not <SAMP>‘char *’</SAMP>, because -it will contain offsets into the string pool instead of actual strings. -To convert such an offset to a string, you can use the expression -<SAMP>‘stringpool + <VAR>o</VAR>’</SAMP>, where <VAR>o</VAR> is the offset. The string pool -name can be changed through the option <SAMP>‘--string-pool-name’</SAMP>. - -<DT><SAMP>‘-Q <VAR>string-pool-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--string-pool-name=<VAR>string-pool-name</VAR>’</SAMP> -<DD> -Allows you to specify the name of the generated string pool created by -option <SAMP>‘-P’</SAMP>. The default name is <SAMP>‘stringpool’</SAMP>. This option -permits the use of two hash tables in the same file, with <SAMP>‘-P’</SAMP> and -even when the option <SAMP>‘-G’</SAMP> (or, equivalently, the <SAMP>‘%global-table’</SAMP> -declaration) is given. - -<DT><SAMP>‘--null-strings’</SAMP> -<DD> -Use NULL strings instead of empty strings for empty keyword table entries. -This reduces the startup time of programs using a shared library containing -the generated code (but not as much as option <SAMP>‘-P’</SAMP>), at the expense -of one more test-and-branch instruction at run time. - -<DT><SAMP>‘-W <VAR>hash-table-array-name</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--word-array-name=<VAR>hash-table-array-name</VAR>’</SAMP> -<DD> -<A NAME="IDX44"></A> -Allows you to specify the name for the generated array containing the -hash table. Default name is <SAMP>‘wordlist’</SAMP>. This option permits the -use of two hash tables in the same file, even when the option <SAMP>‘-G’</SAMP> -(or, equivalently, the <SAMP>‘%global-table’</SAMP> declaration) is given. - -<DT><SAMP>‘--length-table-name=<VAR>length-table-array-name</VAR>’</SAMP> -<DD> -<A NAME="IDX45"></A> -Allows you to specify the name for the generated array containing the -length table. Default name is <SAMP>‘lengthtable’</SAMP>. This option permits the -use of two length tables in the same file, even when the option <SAMP>‘-G’</SAMP> -(or, equivalently, the <SAMP>‘%global-table’</SAMP> declaration) is given. - -<DT><SAMP>‘-S <VAR>total-switch-statements</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--switch=<VAR>total-switch-statements</VAR>’</SAMP> -<DD> -<A NAME="IDX46"></A> -Causes the generated C code to use a <CODE>switch</CODE> statement scheme, -rather than an array lookup table. This can lead to a reduction in both -time and space requirements for some input files. The argument to this -option determines how many <CODE>switch</CODE> statements are generated. A -value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a -value of 2 generates 2 tables with 1/2 the elements in each -<CODE>switch</CODE>, etc. This is useful since many C compilers cannot -correctly generate code for large <CODE>switch</CODE> statements. This option -was inspired in part by Keith Bostic's original C program. - -<DT><SAMP>‘-T’</SAMP> -<DD> -<DT><SAMP>‘--omit-struct-type’</SAMP> -<DD> -Prevents the transfer of the type declaration to the output file. Use -this option if the type is already defined elsewhere. - -<DT><SAMP>‘-p’</SAMP> -<DD> -This option is supported for compatibility with previous releases of -<CODE>gperf</CODE>. It does not do anything. -</DL> - - - -<H2><A NAME="SEC22" HREF="gperf.html#TOC22">5.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2> - -<DL COMPACT> - -<DT><SAMP>‘-k <VAR>selected-byte-positions</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--key-positions=<VAR>selected-byte-positions</VAR>’</SAMP> -<DD> -Allows selection of the byte positions used in the keywords' -hash function. The allowable choices range between 1-255, inclusive. -The positions are separated by commas, e.g., <SAMP>‘-k 9,4,13,14’</SAMP>; -ranges may be used, e.g., <SAMP>‘-k 2-7’</SAMP>; and positions may occur -in any order. Furthermore, the wildcard '*' causes the generated -hash function to consider <STRONG>all</STRONG> byte positions in each keyword, -whereas '$' instructs the hash function to use the “final byte” -of a keyword (this is the only way to use a byte position greater than -255, incidentally). - -For instance, the option <SAMP>‘-k 1,2,4,6-10,'$'’</SAMP> generates a hash -function that considers positions 1,2,4,6,7,8,9,10, plus the last -byte in each keyword (which may be at a different position for each -keyword, obviously). Keywords -with length less than the indicated byte positions work properly, since -selected byte positions exceeding the keyword length are simply not -referenced in the hash function. - -This option is not normally needed since version 2.8 of <CODE>gperf</CODE>; -the default byte positions are computed depending on the keyword set, -through a search that minimizes the number of byte positions. - -<DT><SAMP>‘-D’</SAMP> -<DD> -<DT><SAMP>‘--duplicates’</SAMP> -<DD> -<A NAME="IDX47"></A> -Handle keywords whose selected byte sets hash to duplicate values. -Duplicate hash values can occur if a set of keywords has the same names, but -possesses different attributes, or if the selected byte positions are not well -chosen. With the -D option <CODE>gperf</CODE> treats all these keywords as -part of an equivalence class and generates a perfect hash function with -multiple comparisons for duplicate keywords. It is up to you to completely -disambiguate the keywords by modifying the generated C code. However, -<CODE>gperf</CODE> helps you out by organizing the output. - -Using this option usually means that the generated hash function is no -longer perfect. On the other hand, it permits <CODE>gperf</CODE> to work on -keyword sets that it otherwise could not handle. - -<DT><SAMP>‘-m <VAR>iterations</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--multiple-iterations=<VAR>iterations</VAR>’</SAMP> -<DD> -Perform multiple choices of the <SAMP>‘-i’</SAMP> and <SAMP>‘-j’</SAMP> values, and -choose the best results. This increases the running time by a factor of -<VAR>iterations</VAR> but does a good job minimizing the generated table size. - -<DT><SAMP>‘-i <VAR>initial-value</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--initial-asso=<VAR>initial-value</VAR>’</SAMP> -<DD> -Provides an initial <VAR>value</VAR> for the associate values array. Default -is 0. Increasing the initial value helps inflate the final table size, -possibly leading to more time efficient keyword lookups. Note that this -option is not particularly useful when <SAMP>‘-S’</SAMP> (or, equivalently, -<SAMP>‘%switch’</SAMP>) is used. Also, -<SAMP>‘-i’</SAMP> is overridden when the <SAMP>‘-r’</SAMP> option is used. - -<DT><SAMP>‘-j <VAR>jump-value</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--jump=<VAR>jump-value</VAR>’</SAMP> -<DD> -<A NAME="IDX48"></A> -Affects the “jump value”, i.e., how far to advance the associated -byte value upon collisions. <VAR>Jump-value</VAR> is rounded up to an -odd number, the default is 5. If the <VAR>jump-value</VAR> is 0 <CODE>gperf</CODE> -jumps by random amounts. - -<DT><SAMP>‘-n’</SAMP> -<DD> -<DT><SAMP>‘--no-strlen’</SAMP> -<DD> -Instructs the generator not to include the length of a keyword when -computing its hash value. This may save a few assembly instructions in -the generated lookup table. - -<DT><SAMP>‘-r’</SAMP> -<DD> -<DT><SAMP>‘--random’</SAMP> -<DD> -Utilizes randomness to initialize the associated values table. This -frequently generates solutions faster than using deterministic -initialization (which starts all associated values at 0). Furthermore, -using the randomization option generally increases the size of the -table. - -<DT><SAMP>‘-s <VAR>size-multiple</VAR>’</SAMP> -<DD> -<DT><SAMP>‘--size-multiple=<VAR>size-multiple</VAR>’</SAMP> -<DD> -Affects the size of the generated hash table. The numeric argument for -this option indicates “how many times larger or smaller” the maximum -associated value range should be, in relationship to the number of keywords. -It can be written as an integer, a floating-point number or a fraction. -For example, a value of 3 means “allow the maximum associated value to be -about 3 times larger than the number of input keywords”. -Conversely, a value of 1/3 means “allow the maximum associated value to -be about 3 times smaller than the number of input keywords”. Values -smaller than 1 are useful for limiting the overall size of the generated hash -table, though the option <SAMP>‘-m’</SAMP> is better at this purpose. - -If `generate switch' option <SAMP>‘-S’</SAMP> (or, equivalently, <SAMP>‘%switch’</SAMP>) is -<EM>not</EM> enabled, the maximum -associated value influences the static array table size, and a larger -table should decrease the time required for an unsuccessful search, at -the expense of extra table space. - -The default value is 1, thus the default maximum associated value about -the same size as the number of keywords (for efficiency, the maximum -associated value is always rounded up to a power of 2). The actual -table size may vary somewhat, since this technique is essentially a -heuristic. -</DL> - - - -<H2><A NAME="SEC23" HREF="gperf.html#TOC23">5.6 Informative Output</A></H2> - -<DL COMPACT> - -<DT><SAMP>‘-h’</SAMP> -<DD> -<DT><SAMP>‘--help’</SAMP> -<DD> -Prints a short summary on the meaning of each program option. Aborts -further program execution. - -<DT><SAMP>‘-v’</SAMP> -<DD> -<DT><SAMP>‘--version’</SAMP> -<DD> -Prints out the current version number. - -<DT><SAMP>‘-d’</SAMP> -<DD> -<DT><SAMP>‘--debug’</SAMP> -<DD> -Enables the debugging option. This produces verbose diagnostics to -“standard error” when <CODE>gperf</CODE> is executing. It is useful both for -maintaining the program and for determining whether a given set of -options is actually speeding up the search for a solution. Some useful -information is dumped at the end of the program when the <SAMP>‘-d’</SAMP> -option is enabled. -</DL> - - - -<H1><A NAME="SEC24" HREF="gperf.html#TOC24">6 Known Bugs and Limitations with <CODE>gperf</CODE></A></H1> - -<P> -The following are some limitations with the current release of -<CODE>gperf</CODE>: - -</P> - -<UL> -<LI> - -The <CODE>gperf</CODE> utility is tuned to execute quickly, and works quickly -for small to medium size data sets (around 1000 keywords). It is -extremely useful for maintaining perfect hash functions for compiler -keyword sets. Several recent enhancements now enable <CODE>gperf</CODE> to -work efficiently on much larger keyword sets (over 15,000 keywords). -When processing large keyword sets it helps greatly to have over 8 megs -of RAM. - -<LI> - -The size of the generate static keyword array can get <EM>extremely</EM> -large if the input keyword file is large or if the keywords are quite -similar. This tends to slow down the compilation of the generated C -code, and <EM>greatly</EM> inflates the object code size. If this -situation occurs, consider using the <SAMP>‘-S’</SAMP> option to reduce data -size, potentially increasing keyword recognition time a negligible -amount. Since many C compilers cannot correctly generate code for -large switch statements it is important to qualify the <VAR>-S</VAR> option -with an appropriate numerical argument that controls the number of -switch statements generated. - -<LI> - -The maximum number of selected byte positions has an -arbitrary limit of 255. This restriction should be removed, and if -anyone considers this a problem write me and let me know so I can remove -the constraint. -</UL> - - - -<H1><A NAME="SEC25" HREF="gperf.html#TOC25">7 Things Still Left to Do</A></H1> - -<P> -It should be “relatively” easy to replace the current perfect hash -function algorithm with a more exhaustive approach; the perfect hash -module is essential independent from other program modules. Additional -worthwhile improvements include: - -</P> - -<UL> -<LI> - -Another useful extension involves modifying the program to generate -“minimal” perfect hash functions (under certain circumstances, the -current version can be rather extravagant in the generated table size). -This is mostly of theoretical interest, since a sparse table -often produces faster lookups, and use of the <SAMP>‘-S’</SAMP> <CODE>switch</CODE> -option can minimize the data size, at the expense of slightly longer -lookups (note that the gcc compiler generally produces good code for -<CODE>switch</CODE> statements, reducing the need for more complex schemes). - -<LI> - -In addition to improving the algorithm, it would also be useful to -generate an Ada package as the code output, in addition to the current -C and C++ routines. -</UL> - - - -<H1><A NAME="SEC26" HREF="gperf.html#TOC26">8 Bibliography</A></H1> - -<P> -[1] Chang, C.C.: <I>A Scheme for Constructing Ordered Minimal Perfect -Hashing Functions</I> Information Sciences 39(1986), 187-195. - -</P> -<P> -[2] Cichelli, Richard J. <I>Author's Response to “On Cichelli's Minimal Perfect Hash -Functions Method”</I> Communications of the ACM, 23, 12(December 1980), 729. - -</P> -<P> -[3] Cichelli, Richard J. <I>Minimal Perfect Hash Functions Made Simple</I> -Communications of the ACM, 23, 1(January 1980), 17-19. - -</P> -<P> -[4] Cook, C. R. and Oldehoeft, R.R. <I>A Letter Oriented Minimal -Perfect Hashing Function</I> SIGPLAN Notices, 17, 9(September 1982), 18-27. - -</P> -<P> -[5] Cormack, G. V. and Horspool, R. N. S. and Kaiserwerth, M. -<I>Practical Perfect Hashing</I> Computer Journal, 28, 1(January 1985), 54-58. - -</P> -<P> -[6] Jaeschke, G. <I>Reciprocal Hashing: A Method for Generating Minimal -Perfect Hashing Functions</I> Communications of the ACM, 24, 12(December -1981), 829-833. - -</P> -<P> -[7] Jaeschke, G. and Osterburg, G. <I>On Cichelli's Minimal Perfect -Hash Functions Method</I> Communications of the ACM, 23, 12(December 1980), -728-729. - -</P> -<P> -[8] Sager, Thomas J. <I>A Polynomial Time Generator for Minimal Perfect -Hash Functions</I> Communications of the ACM, 28, 5(December 1985), 523-532 - -</P> -<P> -[9] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I> -Second USENIX C++ Conference Proceedings, April 1990. - -</P> -<P> -[10] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I> -C++ Report, SIGS 10 10 (November/December 1998). - -</P> -<P> -[11] Sebesta, R.W. and Taylor, M.A. <I>Minimal Perfect Hash Functions -for Reserved Word Lists</I> SIGPLAN Notices, 20, 12(September 1985), 47-53. - -</P> -<P> -[12] Sprugnoli, R. <I>Perfect Hashing Functions: A Single Probe -Retrieving Method for Static Sets</I> Communications of the ACM, 20 -11(November 1977), 841-850. - -</P> -<P> -[13] Stallman, Richard M. <I>Using and Porting GNU CC</I> Free Software Foundation, -1988. - -</P> -<P> -[14] Stroustrup, Bjarne <I>The C++ Programming Language.</I> Addison-Wesley, 1986. - -</P> -<P> -[15] Tiemann, Michael D. <I>User's Guide to GNU C++</I> Free Software -Foundation, 1989. - -</P> - - -<H1><A NAME="SEC27" HREF="gperf.html#TOC27">Concept Index</A></H1> - -<P> -Jump to: -<A HREF="#cindex_&">&</A> -- -<A HREF="#cindex_a">a</A> -- -<A HREF="#cindex_b">b</A> -- -<A HREF="#cindex_c">c</A> -- -<A HREF="#cindex_d">d</A> -- -<A HREF="#cindex_f">f</A> -- -<A HREF="#cindex_h">h</A> -- -<A HREF="#cindex_i">i</A> -- -<A HREF="#cindex_j">j</A> -- -<A HREF="#cindex_k">k</A> -- -<A HREF="#cindex_m">m</A> -- -<A HREF="#cindex_n">n</A> -- -<A HREF="#cindex_s">s</A> -<P> -<H2><A NAME="cindex_&">&</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX8"><SAMP>‘%%’</SAMP></A> -<LI><A HREF="gperf.html#IDX18"><SAMP>‘%7bit’</SAMP></A> -<LI><A HREF="gperf.html#IDX19"><SAMP>‘%compare-lengths’</SAMP></A> -<LI><A HREF="gperf.html#IDX20"><SAMP>‘%compare-strncmp’</SAMP></A> -<LI><A HREF="gperf.html#IDX17"><SAMP>‘%define class-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX15"><SAMP>‘%define hash-function-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX14"><SAMP>‘%define initializer-suffix’</SAMP></A> -<LI><A HREF="gperf.html#IDX29"><SAMP>‘%define length-table-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX16"><SAMP>‘%define lookup-function-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX13"><SAMP>‘%define slot-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX26"><SAMP>‘%define string-pool-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX28"><SAMP>‘%define word-array-name’</SAMP></A> -<LI><A HREF="gperf.html#IDX9"><SAMP>‘%delimiters’</SAMP></A> -<LI><A HREF="gperf.html#IDX22"><SAMP>‘%enum’</SAMP></A> -<LI><A HREF="gperf.html#IDX24"><SAMP>‘%global-table’</SAMP></A> -<LI><A HREF="gperf.html#IDX11"><SAMP>‘%ignore-case’</SAMP></A> -<LI><A HREF="gperf.html#IDX23"><SAMP>‘%includes’</SAMP></A> -<LI><A HREF="gperf.html#IDX12"><SAMP>‘%language’</SAMP></A> -<LI><A HREF="gperf.html#IDX27"><SAMP>‘%null-strings’</SAMP></A> -<LI><A HREF="gperf.html#IDX31"><SAMP>‘%omit-struct-type’</SAMP></A> -<LI><A HREF="gperf.html#IDX25"><SAMP>‘%pic’</SAMP></A> -<LI><A HREF="gperf.html#IDX21"><SAMP>‘%readonly-tables’</SAMP></A> -<LI><A HREF="gperf.html#IDX10"><SAMP>‘%struct-type’</SAMP></A> -<LI><A HREF="gperf.html#IDX30"><SAMP>‘%switch’</SAMP></A> -<LI><A HREF="gperf.html#IDX32"><SAMP>‘%{’</SAMP></A> -<LI><A HREF="gperf.html#IDX33"><SAMP>‘%}’</SAMP></A> -</DIR> -<H2><A NAME="cindex_a">a</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX44">Array name</A>, <A HREF="gperf.html#IDX45">Array name</A> -</DIR> -<H2><A NAME="cindex_b">b</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX1">Bugs</A> -</DIR> -<H2><A NAME="cindex_c">c</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX43">Class name</A> -<LI><A HREF="gperf.html#IDX39">Copyright</A> -</DIR> -<H2><A NAME="cindex_d">d</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX5">Declaration section</A> -<LI><A HREF="gperf.html#IDX40">Delimiters</A> -<LI><A HREF="gperf.html#IDX47">Duplicates</A> -</DIR> -<H2><A NAME="cindex_f">f</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX4">Format</A> -<LI><A HREF="gperf.html#IDX7">Functions section</A> -</DIR> -<H2><A NAME="cindex_h">h</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX35">hash</A> -<LI><A HREF="gperf.html#IDX34">hash table</A> -</DIR> -<H2><A NAME="cindex_i">i</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX36">in_word_set</A> -<LI><A HREF="gperf.html#IDX42">Initializers</A> -</DIR> -<H2><A NAME="cindex_j">j</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX48">Jump value</A> -</DIR> -<H2><A NAME="cindex_k">k</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX6">Keywords section</A> -</DIR> -<H2><A NAME="cindex_m">m</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX3">Minimal perfect hash functions</A> -</DIR> -<H2><A NAME="cindex_n">n</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX38">NUL</A> -</DIR> -<H2><A NAME="cindex_s">s</A></H2> -<DIR> -<LI><A HREF="gperf.html#IDX41">Slot name</A> -<LI><A HREF="gperf.html#IDX2">Static search structure</A> -<LI><A HREF="gperf.html#IDX37"><CODE>switch</CODE></A>, <A HREF="gperf.html#IDX46"><CODE>switch</CODE></A> -</DIR> - -</P> - -<P><HR><P> -This document was generated on 20 December 2009 using the -<A HREF="http://wwwinfo.cern.ch/dis/texi2html/">texi2html</A> -translator version 1.52b.</P> -</BODY> -</HTML> |