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Diffstat (limited to 'ext/pcre/pcrelib/HACKING')
| -rw-r--r-- | ext/pcre/pcrelib/HACKING | 288 |
1 files changed, 158 insertions, 130 deletions
diff --git a/ext/pcre/pcrelib/HACKING b/ext/pcre/pcrelib/HACKING index ee0913214c..87b88191ad 100644 --- a/ext/pcre/pcrelib/HACKING +++ b/ext/pcre/pcrelib/HACKING @@ -2,7 +2,8 @@ Technical Notes about PCRE -------------------------- These are very rough technical notes that record potentially useful information -about PCRE internals. +about PCRE internals. For information about testing PCRE, see the pcretest +documentation and the comment at the head of the RunTest file. Historical note 1 @@ -48,6 +49,18 @@ complexity in Perl regular expressions, I couldn't do this. In any case, a first pass through the pattern is helpful for other reasons. +Support for 16-bit data strings +------------------------------- + +From release 8.30, PCRE supports 16-bit as well as 8-bit data strings, by being +compilable in either 8-bit or 16-bit modes, or both. Thus, two different +libraries can be created. In the description that follows, the word "short" is +used for a 16-bit data quantity, and the word "unit" is used for a quantity +that is a byte in 8-bit mode and a short in 16-bit mode. However, so as not to +over-complicate the text, the names of PCRE functions are given in 8-bit form +only. + + Computing the memory requirement: how it was -------------------------------------------- @@ -68,7 +81,7 @@ things I did for 6.8 was to fix Yet Another Bug in the memory computation. Then I had a flash of inspiration as to how I could run the real compile function in a "fake" mode that enables it to compute how much memory it would need, while actually only ever using a few hundred bytes of working memory, and without too -many tests of the mode that might slow it down. So I re-factored the compiling +many tests of the mode that might slow it down. So I refactored the compiling functions to work this way. This got rid of about 600 lines of source. It should make future maintenance and development easier. As this was such a major change, I never released 6.8, instead upping the number to 7.0 (other quite @@ -88,7 +101,10 @@ The "traditional", and original, matching function is called pcre_exec(), and it implements an NFA algorithm, similar to the original Henry Spencer algorithm and the way that Perl works. This is not surprising, since it is intended to be as compatible with Perl as possible. This is the function most users of PCRE -will use most of the time. +will use most of the time. From release 8.20, if PCRE is compiled with +just-in-time (JIT) support, and studying a compiled pattern with JIT is +successful, the JIT code is run instead of the normal pcre_exec() code, but the +result is the same. Supplementary matching function @@ -108,28 +124,38 @@ needed at compile time to produce a traditional FSM where only one state is ever active at once. I believe some other regex matchers work this way. -Format of compiled patterns ---------------------------- +Changeable options +------------------ + +The /i, /m, or /s options (PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL) may +change in the middle of patterns. From PCRE 8.13, their processing is handled +entirely at compile time by generating different opcodes for the different +settings. The runtime functions do not need to keep track of an options state +any more. -The compiled form of a pattern is a vector of bytes, containing items of -variable length. The first byte in an item is an opcode, and the length of the -item is either implicit in the opcode or contained in the data bytes that -follow it. -In many cases below LINK_SIZE data values are specified for offsets within the -compiled pattern. The default value for LINK_SIZE is 2, but PCRE can be -compiled to use 3-byte or 4-byte values for these offsets (impairing the -performance). This is necessary only when patterns whose compiled length is -greater than 64K are going to be processed. In this description, we assume the -"normal" compilation options. Data values that are counts (e.g. for -quantifiers) are always just two bytes long. +Format of compiled patterns +--------------------------- -A list of the opcodes follows: +The compiled form of a pattern is a vector of units (bytes in 8-bit mode, or +shorts in 16-bit mode), containing items of variable length. The first unit in +an item contains an opcode, and the length of the item is either implicit in +the opcode or contained in the data that follows it. + +In many cases listed below, LINK_SIZE data values are specified for offsets +within the compiled pattern. LINK_SIZE always specifies a number of bytes. The +default value for LINK_SIZE is 2, but PCRE can be compiled to use 3-byte or +4-byte values for these offsets, although this impairs the performance. (3-byte +LINK_SIZE values are available only in 8-bit mode.) Specifing a LINK_SIZE +larger than 2 is necessary only when patterns whose compiled length is greater +than 64K are going to be processed. In this description, we assume the "normal" +compilation options. Data values that are counts (e.g. for quantifiers) are +always just two bytes long (one short in 16-bit mode). Opcodes with no following data ------------------------------ -These items are all just one byte long +These items are all just one unit long OP_END end of pattern OP_ANY match any one character other than newline @@ -138,7 +164,8 @@ These items are all just one byte long OP_SOD match start of data: \A OP_SOM, start of match (subject + offset): \G OP_SET_SOM, set start of match (\K) - OP_CIRC ^ (start of data, or after \n in multiline) + OP_CIRC ^ (start of data) + OP_CIRCM ^ multiline mode (start of data or after newline) OP_NOT_WORD_BOUNDARY \W OP_WORD_BOUNDARY \w OP_NOT_DIGIT \D @@ -153,7 +180,8 @@ These items are all just one byte long OP_WORDCHAR \w OP_EODN match end of data or \n at end: \Z OP_EOD match end of data: \z - OP_DOLL $ (end of data, or before \n in multiline) + OP_DOLL $ (end of data, or before final newline) + OP_DOLLM $ multiline mode (end of data or before newline) OP_EXTUNI match an extended Unicode character OP_ANYNL match any Unicode newline sequence @@ -164,49 +192,57 @@ These items are all just one byte long OP_SKIP ) indicating which parentheses must be closed. -Backtracking control verbs with data ------------------------------------- - -OP_THEN is followed by a LINK_SIZE offset, which is the distance back to the -start of the current branch. - -OP_MARK is followed by the mark name, preceded by a one-byte length, and -followed by a binary zero. For (*PRUNE), (*SKIP), and (*THEN) with arguments, -the opcodes OP_PRUNE_ARG, OP_SKIP_ARG, and OP_THEN_ARG are used. For the first -two, the name follows immediately; for OP_THEN_ARG, it follows the LINK_SIZE -offset value. +Backtracking control verbs with (optional) data +----------------------------------------------- + +(*THEN) without an argument generates the opcode OP_THEN and no following data. +OP_MARK is followed by the mark name, preceded by a one-unit length, and +followed by a binary zero. For (*PRUNE), (*SKIP), and (*THEN) with arguments, +the opcodes OP_PRUNE_ARG, OP_SKIP_ARG, and OP_THEN_ARG are used, with the name +following in the same format. -Repeating single characters +Matching literal characters --------------------------- -The common repeats (*, +, ?) when applied to a single character use the -following opcodes: - - OP_STAR - OP_MINSTAR - OP_POSSTAR - OP_PLUS - OP_MINPLUS - OP_POSPLUS - OP_QUERY - OP_MINQUERY - OP_POSQUERY +The OP_CHAR opcode is followed by a single character that is to be matched +casefully. For caseless matching, OP_CHARI is used. In UTF-8 or UTF-16 modes, +the character may be more than one unit long. -In ASCII mode, these are two-byte items; in UTF-8 mode, the length is variable. -Those with "MIN" in their name are the minimizing versions. Those with "POS" in -their names are possessive versions. Each is followed by the character that is -to be repeated. Other repeats make use of - OP_UPTO - OP_MINUPTO - OP_POSUPTO - OP_EXACT +Repeating single characters +--------------------------- -which are followed by a two-byte count (most significant first) and the -repeated character. OP_UPTO matches from 0 to the given number. A repeat with a -non-zero minimum and a fixed maximum is coded as an OP_EXACT followed by an -OP_UPTO (or OP_MINUPTO or OPT_POSUPTO). +The common repeats (*, +, ?), when applied to a single character, use the +following opcodes, which come in caseful and caseless versions: + + Caseful Caseless + OP_STAR OP_STARI + OP_MINSTAR OP_MINSTARI + OP_POSSTAR OP_POSSTARI + OP_PLUS OP_PLUSI + OP_MINPLUS OP_MINPLUSI + OP_POSPLUS OP_POSPLUSI + OP_QUERY OP_QUERYI + OP_MINQUERY OP_MINQUERYI + OP_POSQUERY OP_POSQUERYI + +Each opcode is followed by the character that is to be repeated. In ASCII mode, +these are two-unit items; in UTF-8 or UTF-16 modes, the length is variable. +Those with "MIN" in their names are the minimizing versions. Those with "POS" +in their names are possessive versions. Other repeats make use of these +opcodes: + + Caseful Caseless + OP_UPTO OP_UPTOI + OP_MINUPTO OP_MINUPTOI + OP_POSUPTO OP_POSUPTOI + OP_EXACT OP_EXACTI + +Each of these is followed by a two-byte (one short) count (most significant +byte first in 8-bit mode) and then the repeated character. OP_UPTO matches from +0 to the given number. A repeat with a non-zero minimum and a fixed maximum is +coded as an OP_EXACT followed by an OP_UPTO (or OP_MINUPTO or OPT_POSUPTO). Repeating character types @@ -214,7 +250,7 @@ Repeating character types Repeats of things like \d are done exactly as for single characters, except that instead of a character, the opcode for the type is stored in the data -byte. The opcodes are: +unit. The opcodes are: OP_TYPESTAR OP_TYPEMINSTAR @@ -236,65 +272,58 @@ Match by Unicode property OP_PROP and OP_NOTPROP are used for positive and negative matches of a character by testing its Unicode property (the \p and \P escape sequences). -Each is followed by two bytes that encode the desired property as a type and a +Each is followed by two units that encode the desired property as a type and a value. -Repeats of these items use the OP_TYPESTAR etc. set of opcodes, followed by -three bytes: OP_PROP or OP_NOTPROP and then the desired property type and +Repeats of these items use the OP_TYPESTAR etc. set of opcodes, followed by +three units: OP_PROP or OP_NOTPROP, and then the desired property type and value. -Matching literal characters ---------------------------- - -The OP_CHAR opcode is followed by a single character that is to be matched -casefully. For caseless matching, OP_CHARNC is used. In UTF-8 mode, the -character may be more than one byte long. (Earlier versions of PCRE used -multi-character strings, but this was changed to allow some new features to be -added.) - - Character classes ----------------- -If there is only one character, OP_CHAR or OP_CHARNC is used for a positive -class, and OP_NOT for a negative one (that is, for something like [^a]). -However, in UTF-8 mode, the use of OP_NOT applies only to characters with -values < 128, because OP_NOT is confined to single bytes. +If there is only one character in the class, OP_CHAR or OP_CHARI is used for a +positive class, and OP_NOT or OP_NOTI for a negative one (that is, for +something like [^a]). -Another set of repeating opcodes (OP_NOTSTAR etc.) are used for a repeated, -negated, single-character class. The normal ones (OP_STAR etc.) are used for a -repeated positive single-character class. +Another set of 13 repeating opcodes (called OP_NOTSTAR etc.) are used for +repeated, negated, single-character classes. The normal single-character +opcodes (OP_STAR, etc.) are used for repeated positive single-character +classes. -When there's more than one character in a class and all the characters are less -than 256, OP_CLASS is used for a positive class, and OP_NCLASS for a negative -one. In either case, the opcode is followed by a 32-byte bit map containing a 1 -bit for every character that is acceptable. The bits are counted from the least -significant end of each byte. +When there is more than one character in a class and all the characters are +less than 256, OP_CLASS is used for a positive class, and OP_NCLASS for a +negative one. In either case, the opcode is followed by a 32-byte (16-short) +bit map containing a 1 bit for every character that is acceptable. The bits are +counted from the least significant end of each unit. In caseless mode, bits for +both cases are set. -The reason for having both OP_CLASS and OP_NCLASS is so that, in UTF-8 mode, -subject characters with values greater than 256 can be handled correctly. For -OP_CLASS they don't match, whereas for OP_NCLASS they do. +The reason for having both OP_CLASS and OP_NCLASS is so that, in UTF-8/16 mode, +subject characters with values greater than 255 can be handled correctly. For +OP_CLASS they do not match, whereas for OP_NCLASS they do. -For classes containing characters with values > 255, OP_XCLASS is used. It -optionally uses a bit map (if any characters lie within it), followed by a list -of pairs and single characters. There is a flag character than indicates -whether it's a positive or a negative class. +For classes containing characters with values greater than 255, OP_XCLASS is +used. It optionally uses a bit map (if any characters lie within it), followed +by a list of pairs (for a range) and single characters. In caseless mode, both +cases are explicitly listed. There is a flag character than indicates whether +it is a positive or a negative class. Back references --------------- -OP_REF is followed by two bytes containing the reference number. +OP_REF (caseful) or OP_REFI (caseless) is followed by two bytes (one short) +containing the reference number. Repeating character classes and back references ----------------------------------------------- Single-character classes are handled specially (see above). This section -applies to OP_CLASS and OP_REF. In both cases, the repeat information follows -the base item. The matching code looks at the following opcode to see if it is -one of +applies to OP_CLASS and OP_REF[I]. In both cases, the repeat information +follows the base item. The matching code looks at the following opcode to see +if it is one of OP_CRSTAR OP_CRMINSTAR @@ -305,10 +334,10 @@ one of OP_CRRANGE OP_CRMINRANGE -All but the last two are just single-byte items. The others are followed by -four bytes of data, comprising the minimum and maximum repeat counts. There are -no special possessive opcodes for these repeats; a possessive repeat is -compiled into an atomic group. +All but the last two are just single-unit items. The others are followed by +four bytes (two shorts) of data, comprising the minimum and maximum repeat +counts. There are no special possessive opcodes for these repeats; a possessive +repeat is compiled into an atomic group. Brackets and alternation @@ -318,7 +347,8 @@ A pair of non-capturing (round) brackets is wrapped round each expression at compile time, so alternation always happens in the context of brackets. [Note for North Americans: "bracket" to some English speakers, including -myself, can be round, square, curly, or pointy. Hence this usage.] +myself, can be round, square, curly, or pointy. Hence this usage rather than +"parentheses".] Non-capturing brackets use the opcode OP_BRA. Originally PCRE was limited to 99 capturing brackets and it used a different opcode for each one. From release @@ -330,16 +360,17 @@ A bracket opcode is followed by LINK_SIZE bytes which give the offset to the next alternative OP_ALT or, if there aren't any branches, to the matching OP_KET opcode. Each OP_ALT is followed by LINK_SIZE bytes giving the offset to the next one, or to the OP_KET opcode. For capturing brackets, the bracket -number immediately follows the offset, always as a 2-byte item. +number immediately follows the offset, always as a 2-byte (one short) item. -OP_KET is used for subpatterns that do not repeat indefinitely, while +OP_KET is used for subpatterns that do not repeat indefinitely, and OP_KETRMIN and OP_KETRMAX are used for indefinite repetitions, minimally or -maximally respectively. All three are followed by LINK_SIZE bytes giving (as a -positive number) the offset back to the matching bracket opcode. +maximally respectively (see below for possessive repetitions). All three are +followed by LINK_SIZE bytes giving (as a positive number) the offset back to +the matching bracket opcode. If a subpattern is quantified such that it is permitted to match zero times, it is preceded by one of OP_BRAZERO, OP_BRAMINZERO, or OP_SKIPZERO. These are -single-byte opcodes that tell the matcher that skipping the following +single-unit opcodes that tell the matcher that skipping the following subpattern entirely is a valid branch. In the case of the first two, not skipping the pattern is also valid (greedy and non-greedy). The third is used when a pattern has the quantifier {0,0}. It cannot be entirely discarded, @@ -362,6 +393,15 @@ final replication is changed to OP_SBRA or OP_SCBRA. This tells the matcher that it needs to check for matching an empty string when it hits OP_KETRMIN or OP_KETRMAX, and if so, to break the loop. +Possessive brackets +------------------- + +When a repeated group (capturing or non-capturing) is marked as possessive by +the "+" notation, e.g. (abc)++, different opcodes are used. Their names all +have POS on the end, e.g. OP_BRAPOS instead of OP_BRA and OP_SCPBRPOS instead +of OP_SCBRA. The end of such a group is marked by OP_KETRPOS. If the minimum +repetition is zero, the group is preceded by OP_BRAPOSZERO. + Assertions ---------- @@ -369,11 +409,11 @@ Assertions Forward assertions are just like other subpatterns, but starting with one of the opcodes OP_ASSERT or OP_ASSERT_NOT. Backward assertions use the opcodes OP_ASSERTBACK and OP_ASSERTBACK_NOT, and the first opcode inside the assertion -is OP_REVERSE, followed by a two byte count of the number of characters to move -back the pointer in the subject string. When operating in UTF-8 mode, the count -is a character count rather than a byte count. A separate count is present in -each alternative of a lookbehind assertion, allowing them to have different -fixed lengths. +is OP_REVERSE, followed by a two byte (one short) count of the number of +characters to move back the pointer in the subject string. In ASCII mode, the +count is a number of units, but in UTF-8/16 mode each character may occupy more +than one unit. A separate count is present in each alternative of a lookbehind +assertion, allowing them to have different fixed lengths. Once-only (atomic) subpatterns @@ -390,14 +430,15 @@ Conditional subpatterns These are like other subpatterns, but they start with the opcode OP_COND, or OP_SCOND for one that might match an empty string in an unbounded repeat. If the condition is a back reference, this is stored at the start of the -subpattern using the opcode OP_CREF followed by two bytes containing the -reference number. OP_NCREF is used instead if the reference was generated by -name (so that the runtime code knows to check for duplicate names). +subpattern using the opcode OP_CREF followed by two bytes (one short) +containing the reference number. OP_NCREF is used instead if the reference was +generated by name (so that the runtime code knows to check for duplicate +names). If the condition is "in recursion" (coded as "(?(R)"), or "in recursion of group x" (coded as "(?(Rx)"), the group number is stored at the start of the subpattern using the opcode OP_RREF or OP_NRREF (cf OP_NCREF), and a value of -zero for "the whole pattern". For a DEFINE condition, just the single byte +zero for "the whole pattern". For a DEFINE condition, just the single unit OP_DEF is used (it has no associated data). Otherwise, a conditional subpattern always starts with one of the assertions. @@ -416,25 +457,12 @@ are not strictly a recursion. Callout ------- -OP_CALLOUT is followed by one byte of data that holds a callout number in the +OP_CALLOUT is followed by one unit of data that holds a callout number in the range 0 to 254 for manual callouts, or 255 for an automatic callout. In both -cases there follows a two-byte value giving the offset in the pattern to the -start of the following item, and another two-byte item giving the length of the -next item. - - -Changing options ----------------- +cases there follows a two-byte (one short) value giving the offset in the +pattern to the start of the following item, and another two-byte (one short) +item giving the length of the next item. -If any of the /i, /m, or /s options are changed within a pattern, an OP_OPT -opcode is compiled, followed by one byte containing the new settings of these -flags. If there are several alternatives, there is an occurrence of OP_OPT at -the start of all those following the first options change, to set appropriate -options for the start of the alternative. Immediately after the end of the -group there is another such item to reset the flags to their previous values. A -change of flag right at the very start of the pattern can be handled entirely -at compile time, and so does not cause anything to be put into the compiled -data. Philip Hazel -October 2010 +February 2012 |