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revision 716 by ph10, Tue Oct 4 16:38:05 2011 UTC revision 840 by ph10, Fri Dec 30 19:32:50 2011 UTC
# Line 49  complexity in Perl regular expressions, Line 49  complexity in Perl regular expressions,
49  first pass through the pattern is helpful for other reasons.  first pass through the pattern is helpful for other reasons.
50    
51    
52    Support for 16-bit data strings
53    -------------------------------
54    
55    From release 8.30, PCRE supports 16-bit as well as 8-bit data strings, by being
56    compilable in either 8-bit or 16-bit modes, or both. Thus, two different
57    libraries can be created. In the description that follows, the word "short" is
58    used for a 16-bit data quantity, and the word "unit" is used for a quantity
59    that is a byte in 8-bit mode and a short in 16-bit mode. However, so as not to
60    over-complicate the text, the names of PCRE functions are given in 8-bit form
61    only.
62    
63    
64  Computing the memory requirement: how it was  Computing the memory requirement: how it was
65  --------------------------------------------  --------------------------------------------
66    
# Line 125  any more. Line 137  any more.
137  Format of compiled patterns  Format of compiled patterns
138  ---------------------------  ---------------------------
139    
140  The compiled form of a pattern is a vector of bytes, containing items of  The compiled form of a pattern is a vector of units (bytes in 8-bit mode, or
141  variable length. The first byte in an item is an opcode, and the length of the  shorts in 16-bit mode), containing items of variable length. The first unit in
142  item is either implicit in the opcode or contained in the data bytes that  an item contains an opcode, and the length of the item is either implicit in
143  follow it.  the opcode or contained in the data that follows it.
144    
145  In many cases below LINK_SIZE data values are specified for offsets within the  In many cases listed below, LINK_SIZE data values are specified for offsets
146  compiled pattern. The default value for LINK_SIZE is 2, but PCRE can be  within the compiled pattern. LINK_SIZE always specifies a number of bytes. The
147  compiled to use 3-byte or 4-byte values for these offsets (impairing the  default value for LINK_SIZE is 2, but PCRE can be compiled to use 3-byte or
148  performance). This is necessary only when patterns whose compiled length is  4-byte values for these offsets, although this impairs the performance. (3-byte
149  greater than 64K are going to be processed. In this description, we assume the  LINK_SIZE values are available only in 8-bit mode.) Specifing a LINK_SIZE
150  "normal" compilation options. Data values that are counts (e.g. for  larger than 2 is necessary only when patterns whose compiled length is greater
151  quantifiers) are always just two bytes long.  than 64K are going to be processed. In this description, we assume the "normal"
152    compilation options. Data values that are counts (e.g. for quantifiers) are
153    always just two bytes long (one short in 16-bit mode).
154    
155  Opcodes with no following data  Opcodes with no following data
156  ------------------------------  ------------------------------
157    
158  These items are all just one byte long  These items are all just one unit long
159    
160    OP_END                 end of pattern    OP_END                 end of pattern
161    OP_ANY                 match any one character other than newline    OP_ANY                 match any one character other than newline
# Line 182  Backtracking control verbs with (optiona Line 196  Backtracking control verbs with (optiona
196  -----------------------------------------------  -----------------------------------------------
197    
198  (*THEN) without an argument generates the opcode OP_THEN and no following data.  (*THEN) without an argument generates the opcode OP_THEN and no following data.
199  OP_MARK is followed by the mark name, preceded by a one-byte length, and  OP_MARK is followed by the mark name, preceded by a one-unit length, and
200  followed by a binary zero. For (*PRUNE), (*SKIP), and (*THEN) with arguments,  followed by a binary zero. For (*PRUNE), (*SKIP), and (*THEN) with arguments,
201  the opcodes OP_PRUNE_ARG, OP_SKIP_ARG, and OP_THEN_ARG are used, with the name  the opcodes OP_PRUNE_ARG, OP_SKIP_ARG, and OP_THEN_ARG are used, with the name
202  following in the same format.  following in the same format.
# Line 192  Matching literal characters Line 206  Matching literal characters
206  ---------------------------  ---------------------------
207    
208  The OP_CHAR opcode is followed by a single character that is to be matched  The OP_CHAR opcode is followed by a single character that is to be matched
209  casefully. For caseless matching, OP_CHARI is used. In UTF-8 mode, the  casefully. For caseless matching, OP_CHARI is used. In UTF-8 or UTF-16 modes,
210  character may be more than one byte long. (Earlier versions of PCRE used  the character may be more than one unit long.
 multi-character strings, but this was changed to allow some new features to be  
 added.)  
211    
212    
213  Repeating single characters  Repeating single characters
214  ---------------------------  ---------------------------
215    
216  The common repeats (*, +, ?) when applied to a single character use the  The common repeats (*, +, ?), when applied to a single character, use the
217  following opcodes, which come in caseful and caseless versions:  following opcodes, which come in caseful and caseless versions:
218    
219    Caseful         Caseless    Caseful         Caseless
# Line 215  following opcodes, which come in caseful Line 227  following opcodes, which come in caseful
227    OP_MINQUERY     OP_MINQUERYI    OP_MINQUERY     OP_MINQUERYI
228    OP_POSQUERY     OP_POSQUERYI    OP_POSQUERY     OP_POSQUERYI
229    
230  In ASCII mode, these are two-byte items; in UTF-8 mode, the length is variable.  Each opcode is followed by the character that is to be repeated. In ASCII mode,
231  Those with "MIN" in their name are the minimizing versions. Those with "POS" in  these are two-unit items; in UTF-8 or UTF-16 modes, the length is variable.
232  their names are possessive versions. Each is followed by the character that is  Those with "MIN" in their names are the minimizing versions. Those with "POS"
233  to be repeated. Other repeats make use of these opcodes:  in their names are possessive versions. Other repeats make use of these
234    opcodes:
235    
236    Caseful         Caseless    Caseful         Caseless
237    OP_UPTO         OP_UPTOI    OP_UPTO         OP_UPTOI
# Line 226  to be repeated. Other repeats make use o Line 239  to be repeated. Other repeats make use o
239    OP_POSUPTO      OP_POSUPTOI    OP_POSUPTO      OP_POSUPTOI
240    OP_EXACT        OP_EXACTI    OP_EXACT        OP_EXACTI
241    
242  Each of these is followed by a two-byte count (most significant first) and the  Each of these is followed by a two-byte (one short) count (most significant
243  repeated character. OP_UPTO matches from 0 to the given number. A repeat with a  byte first in 8-bit mode) and then the repeated character. OP_UPTO matches from
244  non-zero minimum and a fixed maximum is coded as an OP_EXACT followed by an  0 to the given number. A repeat with a non-zero minimum and a fixed maximum is
245  OP_UPTO (or OP_MINUPTO or OPT_POSUPTO).  coded as an OP_EXACT followed by an OP_UPTO (or OP_MINUPTO or OPT_POSUPTO).
246    
247    
248  Repeating character types  Repeating character types
# Line 237  Repeating character types Line 250  Repeating character types
250    
251  Repeats of things like \d are done exactly as for single characters, except  Repeats of things like \d are done exactly as for single characters, except
252  that instead of a character, the opcode for the type is stored in the data  that instead of a character, the opcode for the type is stored in the data
253  byte. The opcodes are:  unit. The opcodes are:
254    
255    OP_TYPESTAR    OP_TYPESTAR
256    OP_TYPEMINSTAR    OP_TYPEMINSTAR
# Line 259  Match by Unicode property Line 272  Match by Unicode property
272    
273  OP_PROP and OP_NOTPROP are used for positive and negative matches of a  OP_PROP and OP_NOTPROP are used for positive and negative matches of a
274  character by testing its Unicode property (the \p and \P escape sequences).  character by testing its Unicode property (the \p and \P escape sequences).
275  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
276  value.  value.
277    
278  Repeats of these items use the OP_TYPESTAR etc. set of opcodes, followed by  Repeats of these items use the OP_TYPESTAR etc. set of opcodes, followed by
279  three bytes: OP_PROP or OP_NOTPROP and then the desired property type and  three units: OP_PROP or OP_NOTPROP, and then the desired property type and
280  value.  value.
281    
282    
283  Character classes  Character classes
284  -----------------  -----------------
285    
286  If there is only one character, OP_CHAR or OP_CHARI is used for a positive  If there is only one character in the class, OP_CHAR or OP_CHARI is used for a
287  class, and OP_NOT or OP_NOTI for a negative one (that is, for something like  positive class, and OP_NOT or OP_NOTI for a negative one (that is, for
288  [^a]). However, in UTF-8 mode, the use of OP_NOT[I] applies only to characters  something like [^a]). However, OP_NOT[I] can be used only with single-unit
289  with values < 128, because OP_NOT[I] is confined to single bytes.  characters, so in UTF-8 (UTF-16) mode, the use of OP_NOT[I] applies only to
290    characters whose code points are no greater than 127 (0xffff).
291  Another set of 13 repeating opcodes (called OP_NOTSTAR etc.) are used for a  
292  repeated, negated, single-character class. The normal single-character opcodes  Another set of 13 repeating opcodes (called OP_NOTSTAR etc.) are used for
293  (OP_STAR, etc.) are used for a repeated positive single-character class.  repeated, negated, single-character classes. The normal single-character
294    opcodes (OP_STAR, etc.) are used for repeated positive single-character
295    classes.
296    
297  When there is more than one character in a class and all the characters are  When there is more than one character in a class and all the characters are
298  less than 256, OP_CLASS is used for a positive class, and OP_NCLASS for a  less than 256, OP_CLASS is used for a positive class, and OP_NCLASS for a
299  negative one. In either case, the opcode is followed by a 32-byte bit map  negative one. In either case, the opcode is followed by a 32-byte (16-short)
300  containing a 1 bit for every character that is acceptable. The bits are counted  bit map containing a 1 bit for every character that is acceptable. The bits are
301  from the least significant end of each byte. In caseless mode, bits for both  counted from the least significant end of each unit. In caseless mode, bits for
302  cases are set.  both cases are set.
303    
304  The reason for having both OP_CLASS and OP_NCLASS is so that, in UTF-8 mode,  The reason for having both OP_CLASS and OP_NCLASS is so that, in UTF-8/16 mode,
305  subject characters with values greater than 256 can be handled correctly. For  subject characters with values greater than 255 can be handled correctly. For
306  OP_CLASS they do not match, whereas for OP_NCLASS they do.  OP_CLASS they do not match, whereas for OP_NCLASS they do.
307    
308  For classes containing characters with values > 255, OP_XCLASS is used. It  For classes containing characters with values greater than 255, OP_XCLASS is
309  optionally uses a bit map (if any characters lie within it), followed by a list  used. It optionally uses a bit map (if any characters lie within it), followed
310  of pairs (for a range) and single characters. In caseless mode, both cases are  by a list of pairs (for a range) and single characters. In caseless mode, both
311  explicitly listed. There is a flag character than indicates whether it is a  cases are explicitly listed. There is a flag character than indicates whether
312  positive or a negative class.  it is a positive or a negative class.
313    
314    
315  Back references  Back references
316  ---------------  ---------------
317    
318  OP_REF (caseful) or OP_REFI (caseless) is followed by two bytes containing the  OP_REF (caseful) or OP_REFI (caseless) is followed by two bytes (one short)
319  reference number.  containing the reference number.
320    
321    
322  Repeating character classes and back references  Repeating character classes and back references
# Line 321  if it is one of Line 336  if it is one of
336    OP_CRRANGE    OP_CRRANGE
337    OP_CRMINRANGE    OP_CRMINRANGE
338    
339  All but the last two are just single-byte items. The others are followed by  All but the last two are just single-unit items. The others are followed by
340  four bytes of data, comprising the minimum and maximum repeat counts. There are  four bytes (two shorts) of data, comprising the minimum and maximum repeat
341  no special possessive opcodes for these repeats; a possessive repeat is  counts. There are no special possessive opcodes for these repeats; a possessive
342  compiled into an atomic group.  repeat is compiled into an atomic group.
343    
344    
345  Brackets and alternation  Brackets and alternation
# Line 334  A pair of non-capturing (round) brackets Line 349  A pair of non-capturing (round) brackets
349  compile time, so alternation always happens in the context of brackets.  compile time, so alternation always happens in the context of brackets.
350    
351  [Note for North Americans: "bracket" to some English speakers, including  [Note for North Americans: "bracket" to some English speakers, including
352  myself, can be round, square, curly, or pointy. Hence this usage.]  myself, can be round, square, curly, or pointy. Hence this usage rather than
353    "parentheses".]
354    
355  Non-capturing brackets use the opcode OP_BRA. Originally PCRE was limited to 99  Non-capturing brackets use the opcode OP_BRA. Originally PCRE was limited to 99
356  capturing brackets and it used a different opcode for each one. From release  capturing brackets and it used a different opcode for each one. From release
# Line 346  A bracket opcode is followed by LINK_SIZ Line 362  A bracket opcode is followed by LINK_SIZ
362  next alternative OP_ALT or, if there aren't any branches, to the matching  next alternative OP_ALT or, if there aren't any branches, to the matching
363  OP_KET opcode. Each OP_ALT is followed by LINK_SIZE bytes giving the offset to  OP_KET opcode. Each OP_ALT is followed by LINK_SIZE bytes giving the offset to
364  the next one, or to the OP_KET opcode. For capturing brackets, the bracket  the next one, or to the OP_KET opcode. For capturing brackets, the bracket
365  number immediately follows the offset, always as a 2-byte item.  number immediately follows the offset, always as a 2-byte (one short) item.
366    
367  OP_KET is used for subpatterns that do not repeat indefinitely, while  OP_KET is used for subpatterns that do not repeat indefinitely, and
368  OP_KETRMIN and OP_KETRMAX are used for indefinite repetitions, minimally or  OP_KETRMIN and OP_KETRMAX are used for indefinite repetitions, minimally or
369  maximally respectively (see below for possessive repetitions). All three are  maximally respectively (see below for possessive repetitions). All three are
370  followed by LINK_SIZE bytes giving (as a positive number) the offset back to  followed by LINK_SIZE bytes giving (as a positive number) the offset back to
# Line 356  the matching bracket opcode. Line 372  the matching bracket opcode.
372    
373  If a subpattern is quantified such that it is permitted to match zero times, it  If a subpattern is quantified such that it is permitted to match zero times, it
374  is preceded by one of OP_BRAZERO, OP_BRAMINZERO, or OP_SKIPZERO. These are  is preceded by one of OP_BRAZERO, OP_BRAMINZERO, or OP_SKIPZERO. These are
375  single-byte opcodes that tell the matcher that skipping the following  single-unit opcodes that tell the matcher that skipping the following
376  subpattern entirely is a valid branch. In the case of the first two, not  subpattern entirely is a valid branch. In the case of the first two, not
377  skipping the pattern is also valid (greedy and non-greedy). The third is used  skipping the pattern is also valid (greedy and non-greedy). The third is used
378  when a pattern has the quantifier {0,0}. It cannot be entirely discarded,  when a pattern has the quantifier {0,0}. It cannot be entirely discarded,
# Line 395  Assertions Line 411  Assertions
411  Forward assertions are just like other subpatterns, but starting with one of  Forward assertions are just like other subpatterns, but starting with one of
412  the opcodes OP_ASSERT or OP_ASSERT_NOT. Backward assertions use the opcodes  the opcodes OP_ASSERT or OP_ASSERT_NOT. Backward assertions use the opcodes
413  OP_ASSERTBACK and OP_ASSERTBACK_NOT, and the first opcode inside the assertion  OP_ASSERTBACK and OP_ASSERTBACK_NOT, and the first opcode inside the assertion
414  is OP_REVERSE, followed by a two byte count of the number of characters to move  is OP_REVERSE, followed by a two byte (one short) count of the number of
415  back the pointer in the subject string. When operating in UTF-8 mode, the count  characters to move back the pointer in the subject string. In ASCII mode, the
416  is a character count rather than a byte count. A separate count is present in  count is a number of units, but in UTF-8/16 mode each character may occupy more
417  each alternative of a lookbehind assertion, allowing them to have different  than one unit. A separate count is present in each alternative of a lookbehind
418  fixed lengths.  assertion, allowing them to have different fixed lengths.
419    
420    
421  Once-only (atomic) subpatterns  Once-only (atomic) subpatterns
# Line 416  Conditional subpatterns Line 432  Conditional subpatterns
432  These are like other subpatterns, but they start with the opcode OP_COND, or  These are like other subpatterns, but they start with the opcode OP_COND, or
433  OP_SCOND for one that might match an empty string in an unbounded repeat. If  OP_SCOND for one that might match an empty string in an unbounded repeat. If
434  the condition is a back reference, this is stored at the start of the  the condition is a back reference, this is stored at the start of the
435  subpattern using the opcode OP_CREF followed by two bytes containing the  subpattern using the opcode OP_CREF followed by two bytes (one short)
436  reference number. OP_NCREF is used instead if the reference was generated by  containing the reference number. OP_NCREF is used instead if the reference was
437  name (so that the runtime code knows to check for duplicate names).  generated by name (so that the runtime code knows to check for duplicate
438    names).
439    
440  If the condition is "in recursion" (coded as "(?(R)"), or "in recursion of  If the condition is "in recursion" (coded as "(?(R)"), or "in recursion of
441  group x" (coded as "(?(Rx)"), the group number is stored at the start of the  group x" (coded as "(?(Rx)"), the group number is stored at the start of the
442  subpattern using the opcode OP_RREF or OP_NRREF (cf OP_NCREF), and a value of  subpattern using the opcode OP_RREF or OP_NRREF (cf OP_NCREF), and a value of
443  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
444  OP_DEF is used (it has no associated data). Otherwise, a conditional subpattern  OP_DEF is used (it has no associated data). Otherwise, a conditional subpattern
445  always starts with one of the assertions.  always starts with one of the assertions.
446    
# Line 442  are not strictly a recursion. Line 459  are not strictly a recursion.
459  Callout  Callout
460  -------  -------
461    
462  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
463  range 0 to 254 for manual callouts, or 255 for an automatic callout. In both  range 0 to 254 for manual callouts, or 255 for an automatic callout. In both
464  cases there follows a two-byte value giving the offset in the pattern to the  cases there follows a two-byte (one short) value giving the offset in the
465  start of the following item, and another two-byte item giving the length of the  pattern to the start of the following item, and another two-byte (one short)
466  next item.  item giving the length of the next item.
467    
468    
469  Philip Hazel  Philip Hazel
470  October 2011  December 2011

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