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revision 49 by nigel, Sat Feb 24 21:39:33 2007 UTC revision 53 by nigel, Sat Feb 24 21:39:42 2007 UTC
# Line 135  end of each byte. Line 135  end of each byte.
135  Back references  Back references
136  ---------------  ---------------
137    
138  OP_REF is followed by a single byte containing the reference number.  OP_REF is followed by two bytes containing the reference number.
139    
140    
141  Repeating character classes and back references  Repeating character classes and back references
# Line 163  Brackets and alternation Line 163  Brackets and alternation
163    
164  A pair of non-capturing (round) brackets is wrapped round each expression at  A pair of non-capturing (round) brackets is wrapped round each expression at
165  compile time, so alternation always happens in the context of brackets.  compile time, so alternation always happens in the context of brackets.
166    
167  Non-capturing brackets use the opcode OP_BRA, while capturing brackets use  Non-capturing brackets use the opcode OP_BRA, while capturing brackets use
168  OP_BRA+1, OP_BRA+2, etc. [Note for North Americans: "bracket" to some English  OP_BRA+1, OP_BRA+2, etc. [Note for North Americans: "bracket" to some English
169  speakers, including myself, can be round, square, curly, or pointy. Hence this  speakers, including myself, can be round, square, curly, or pointy. Hence this
170  usage.]  usage.]
171    
172    Originally PCRE was limited to 99 capturing brackets (so as not to use up all
173    the opcodes). From release 3.5, there is no limit. What happens is that the
174    first ones, up to EXTRACT_BASIC_MAX are handled with separate opcodes, as
175    above. If there are more, the opcode is set to EXTRACT_BASIC_MAX+1, and the
176    first operation in the bracket is OP_BRANUMBER, followed by a 2-byte bracket
177    number. This opcode is ignored while matching, but is fished out when handling
178    the bracket itself. (They could have all been done like this, but I was making
179    minimal changes.)
180    
181  A bracket opcode is followed by two bytes which give the offset to the next  A bracket opcode is followed by two bytes which give the offset to the next
182  alternative OP_ALT or, if there aren't any branches, to the matching KET  alternative OP_ALT or, if there aren't any branches, to the matching KET
183  opcode. Each OP_ALT is followed by two bytes giving the offset to the next one,  opcode. Each OP_ALT is followed by two bytes giving the offset to the next one,
# Line 191  appropriate. Line 201  appropriate.
201  A subpattern with a bounded maximum repetition is replicated in a nested  A subpattern with a bounded maximum repetition is replicated in a nested
202  fashion up to the maximum number of times, with BRAZERO or BRAMINZERO before  fashion up to the maximum number of times, with BRAZERO or BRAMINZERO before
203  each replication after the minimum, so that, for example, (abc){2,5} is  each replication after the minimum, so that, for example, (abc){2,5} is
204  compiled as (abc)(abc)((abc)((abc)(abc)?)?)?. The 200-bracket limit does not  compiled as (abc)(abc)((abc)((abc)(abc)?)?)?. The 99 and 200 bracket limits do
205  apply to these internally generated brackets.  not apply to these internally generated brackets.
206    
207    
208  Assertions  Assertions
# Line 220  Conditional subpatterns Line 230  Conditional subpatterns
230    
231  These are like other subpatterns, but they start with the opcode OP_COND. If  These are like other subpatterns, but they start with the opcode OP_COND. If
232  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
233  subpattern using the opcode OP_CREF followed by one byte containing the  subpattern using the opcode OP_CREF followed by two bytes containing the
234  reference number. Otherwise, a conditional subpattern will always start with  reference number. Otherwise, a conditional subpattern will always start with
235  one of the assertions.  one of the assertions.
236    
# Line 240  the compiled data. Line 250  the compiled data.
250    
251    
252  Philip Hazel  Philip Hazel
253  August 2000  August 2001
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