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Diffstat (limited to 'libc/regexp/README')
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diff --git a/libc/regexp/README b/libc/regexp/README new file mode 100644 index 0000000..37d6f51 --- /dev/null +++ b/libc/regexp/README @@ -0,0 +1,84 @@ +This is a nearly-public-domain reimplementation of the V8 regexp(3) package. +It gives C programs the ability to use egrep-style regular expressions, and +does it in a much cleaner fashion than the analogous routines in SysV. + + Copyright (c) 1986 by University of Toronto. + Written by Henry Spencer. Not derived from licensed software. + + Permission is granted to anyone to use this software for any + purpose on any computer system, and to redistribute it freely, + subject to the following restrictions: + + 1. The author is not responsible for the consequences of use of + this software, no matter how awful, even if they arise + from defects in it. + + 2. The origin of this software must not be misrepresented, either + by explicit claim or by omission. + + 3. Altered versions must be plainly marked as such, and must not + be misrepresented as being the original software. + +Barring a couple of small items in the BUGS list, this implementation is +believed 100% compatible with V8. It should even be binary-compatible, +sort of, since the only fields in a "struct regexp" that other people have +any business touching are declared in exactly the same way at the same +location in the struct (the beginning). + +This implementation is *NOT* AT&T/Bell code, and is not derived from licensed +software. Even though U of T is a V8 licensee. This software is based on +a V8 manual page sent to me by Dennis Ritchie (the manual page enclosed +here is a complete rewrite and hence is not covered by AT&T copyright). +The software was nearly complete at the time of arrival of our V8 tape. +I haven't even looked at V8 yet, although a friend elsewhere at U of T has +been kind enough to run a few test programs using the V8 regexp(3) to resolve +a few fine points. I admit to some familiarity with regular-expression +implementations of the past, but the only one that this code traces any +ancestry to is the one published in Kernighan & Plauger (from which this +one draws ideas but not code). + +Simplistically: put this stuff into a source directory, copy regexp.h into +/usr/include, inspect Makefile for compilation options that need changing +to suit your local environment, and then do "make r". This compiles the +regexp(3) functions, compiles a test program, and runs a large set of +regression tests. If there are no complaints, then put regexp.o, regsub.o, +and regerror.o into your C library, and regexp.3 into your manual-pages +directory. + +Note that if you don't put regexp.h into /usr/include *before* compiling, +you'll have to add "-I." to CFLAGS before compiling. + +The files are: + +Makefile instructions to make everything +regexp.3 manual page +regexp.h header file, for /usr/include +regexp.c source for regcomp() and regexec() +regsub.c source for regsub() +regerror.c source for default regerror() +regmagic.h internal header file +try.c source for test program +timer.c source for timing program +tests test list for try and timer + +This implementation uses nondeterministic automata rather than the +deterministic ones found in some other implementations, which makes it +simpler, smaller, and faster at compiling regular expressions, but slower +at executing them. In theory, anyway. This implementation does employ +some special-case optimizations to make the simpler cases (which do make +up the bulk of regular expressions actually used) run quickly. In general, +if you want blazing speed you're in the wrong place. Replacing the insides +of egrep with this stuff is probably a mistake; if you want your own egrep +you're going to have to do a lot more work. But if you want to use regular +expressions a little bit in something else, you're in luck. Note that many +existing text editors use nondeterministic regular-expression implementations, +so you're in good company. + +This stuff should be pretty portable, given appropriate option settings. +If your chars have less than 8 bits, you're going to have to change the +internal representation of the automaton, although knowledge of the details +of this is fairly localized. There are no "reserved" char values except for +NUL, and no special significance is attached to the top bit of chars. +The string(3) functions are used a fair bit, on the grounds that they are +probably faster than coding the operations in line. Some attempts at code +tuning have been made, but this is invariably a bit machine-specific. |