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diff --git a/doc/pcre2limits.3 b/doc/pcre2limits.3 new file mode 100644 index 00000000..9bf3626d --- /dev/null +++ b/doc/pcre2limits.3 @@ -0,0 +1,72 @@ +.TH PCRE2LIMITS 3 "03 February 2019" "PCRE2 10.33" +.SH NAME +PCRE2 - Perl-compatible regular expressions (revised API) +.SH "SIZE AND OTHER LIMITATIONS" +.rs +.sp +There are some size limitations in PCRE2 but it is hoped that they will never +in practice be relevant. +.P +The maximum size of a compiled pattern is approximately 64 thousand code units +for the 8-bit and 16-bit libraries if PCRE2 is compiled with the default +internal linkage size, which is 2 bytes for these libraries. If you want to +process regular expressions that are truly enormous, you can compile PCRE2 with +an internal linkage size of 3 or 4 (when building the 16-bit library, 3 is +rounded up to 4). See the \fBREADME\fP file in the source distribution and the +.\" HREF +\fBpcre2build\fP +.\" +documentation for details. In these cases the limit is substantially larger. +However, the speed of execution is slower. In the 32-bit library, the internal +linkage size is always 4. +.P +The maximum length of a source pattern string is essentially unlimited; it is +the largest number a PCRE2_SIZE variable can hold. However, the program that +calls \fBpcre2_compile()\fP can specify a smaller limit. +.P +The maximum length (in code units) of a subject string is one less than the +largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned +integer type, usually defined as size_t. Its maximum value (that is +~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings +and unset offsets. +.P +All values in repeating quantifiers must be less than 65536. +.P +The maximum length of a lookbehind assertion is 65535 characters. +.P +There is no limit to the number of parenthesized groups, but there can be no +more than 65535 capture groups, and there is a limit to the depth of nesting of +parenthesized subpatterns of all kinds. This is imposed in order to limit the +amount of system stack used at compile time. The default limit can be specified +when PCRE2 is built; if not, the default is set to 250. An application can +change this limit by calling pcre2_set_parens_nest_limit() to set the limit in +a compile context. +.P +The maximum length of name for a named capture group is 32 code units, and the +maximum number of such groups is 10000. +.P +The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb +is 255 code units for the 8-bit library and 65535 code units for the 16-bit and +32-bit libraries. +.P +The maximum length of a string argument to a callout is the largest number a +32-bit unsigned integer can hold. +. +. +.SH AUTHOR +.rs +.sp +.nf +Philip Hazel +University Computing Service +Cambridge, England. +.fi +. +. +.SH REVISION +.rs +.sp +.nf +Last updated: 02 February 2019 +Copyright (c) 1997-2019 University of Cambridge. +.fi |