mirror of https://github.com/postgres/postgres
Tatsuo Ishii
25 years ago
parent
a2a0f7b79b
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219bd1e4fb
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/*-------------------------------------------------------------------------
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* |
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* like_match.c |
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* like expression handling internal code. |
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* |
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* This file is included by like.c *twice* if multibyte is enabled. |
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* This is for an optimization of single byte encodings. |
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* Before the inclusion, we need to define following macros: |
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* |
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* CHAREQ |
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* ICHAREQ |
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* NextChar |
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* CopyAdvChar |
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* MatchText (MBMatchText) |
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* MatchTextIC (MBMatchTextIC) |
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* do_like_escape (MB_do_like_escape) |
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* |
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* Copyright (c) 1996-2001, PostgreSQL Global Development Group |
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* |
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* IDENTIFICATION |
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* $Header: /cvsroot/pgsql/src/backend/utils/adt/like_match.c,v 1.1 2001/10/04 02:15:47 ishii Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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/*
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** Originally written by Rich $alz, mirror!rs, Wed Nov 26 19:03:17 EST 1986. |
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** Rich $alz is now <rsalz@bbn.com>. |
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** Special thanks to Lars Mathiesen <thorinn@diku.dk> for the LABORT code. |
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** |
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** This code was shamelessly stolen from the "pql" code by myself and |
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** slightly modified :) |
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** |
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** All references to the word "star" were replaced by "percent" |
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** All references to the word "wild" were replaced by "like" |
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** |
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** All the nice shell RE matching stuff was replaced by just "_" and "%" |
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** |
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** As I don't have a copy of the SQL standard handy I wasn't sure whether |
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** to leave in the '\' escape character handling. |
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** |
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** Keith Parks. <keith@mtcc.demon.co.uk> |
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** |
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** SQL92 lets you specify the escape character by saying |
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** LIKE <pattern> ESCAPE <escape character>. We are a small operation |
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** so we force you to use '\'. - ay 7/95 |
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** |
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** Now we have the like_escape() function that converts patterns with |
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** any specified escape character (or none at all) to the internal |
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** default escape character, which is still '\'. - tgl 9/2000 |
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** |
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** The code is rewritten to avoid requiring null-terminated strings, |
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** which in turn allows us to leave out some memcpy() operations. |
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** This code should be faster and take less memory, but no promises... |
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** - thomas 2000-08-06 |
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** |
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*/ |
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/*--------------------
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* Match text and p, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT. |
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* |
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* LIKE_TRUE: they match |
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* LIKE_FALSE: they don't match |
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* LIKE_ABORT: not only don't they match, but the text is too short. |
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* |
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* If LIKE_ABORT is returned, then no suffix of the text can match the |
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* pattern either, so an upper-level % scan can stop scanning now. |
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*-------------------- |
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*/ |
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static int |
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MatchText(unsigned char *t, int tlen, unsigned char *p, int plen) |
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{ |
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/* Fast path for match-everything pattern */ |
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if ((plen == 1) && (*p == '%')) |
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return LIKE_TRUE; |
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while ((tlen > 0) && (plen > 0)) |
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{ |
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if (*p == '\\') |
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{ |
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/* Next pattern char must match literally, whatever it is */ |
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NextChar(p, plen); |
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if ((plen <= 0) || !CHAREQ(t, p)) |
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return LIKE_FALSE; |
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} |
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else if (*p == '%') |
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{ |
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/* %% is the same as % according to the SQL standard */ |
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/* Advance past all %'s */ |
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while ((plen > 0) && (*p == '%')) |
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NextChar(p, plen); |
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/* Trailing percent matches everything. */ |
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if (plen <= 0) |
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return LIKE_TRUE; |
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/*
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* Otherwise, scan for a text position at which we can match |
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* the rest of the pattern. |
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*/ |
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while (tlen > 0) |
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{ |
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/*
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* Optimization to prevent most recursion: don't recurse |
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* unless first pattern char might match this text char. |
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*/ |
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if (CHAREQ(t, p) || (*p == '\\') || (*p == '_')) |
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{ |
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int matched = MatchText(t, tlen, p, plen); |
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if (matched != LIKE_FALSE) |
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return matched; /* TRUE or ABORT */ |
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} |
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NextChar(t, tlen); |
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} |
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/*
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* End of text with no match, so no point in trying later |
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* places to start matching this pattern. |
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*/ |
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return LIKE_ABORT; |
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} |
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else if ((*p != '_') && !CHAREQ(t, p)) |
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{ |
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/*
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* Not the single-character wildcard and no explicit match? |
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* Then time to quit... |
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*/ |
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return LIKE_FALSE; |
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} |
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NextChar(t, tlen); |
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NextChar(p, plen); |
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} |
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if (tlen > 0) |
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return LIKE_FALSE; /* end of pattern, but not of text */ |
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/* End of input string. Do we have matching pattern remaining? */ |
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while ((plen > 0) && (*p == '%')) /* allow multiple %'s at end of
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* pattern */ |
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NextChar(p, plen); |
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if (plen <= 0) |
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return LIKE_TRUE; |
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/*
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* End of text with no match, so no point in trying later places to |
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* start matching this pattern. |
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*/ |
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return LIKE_ABORT; |
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} /* MatchText() */ |
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/*
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* Same as above, but ignore case |
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*/ |
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static int |
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MatchTextIC(unsigned char *t, int tlen, unsigned char *p, int plen) |
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{ |
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/* Fast path for match-everything pattern */ |
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if ((plen == 1) && (*p == '%')) |
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return LIKE_TRUE; |
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while ((tlen > 0) && (plen > 0)) |
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{ |
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if (*p == '\\') |
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{ |
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/* Next pattern char must match literally, whatever it is */ |
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NextChar(p, plen); |
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if ((plen <= 0) || !ICHAREQ(t, p)) |
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return LIKE_FALSE; |
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} |
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else if (*p == '%') |
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{ |
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/* %% is the same as % according to the SQL standard */ |
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/* Advance past all %'s */ |
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while ((plen > 0) && (*p == '%')) |
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NextChar(p, plen); |
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/* Trailing percent matches everything. */ |
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if (plen <= 0) |
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return LIKE_TRUE; |
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/*
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* Otherwise, scan for a text position at which we can match |
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* the rest of the pattern. |
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*/ |
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while (tlen > 0) |
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{ |
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/*
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* Optimization to prevent most recursion: don't recurse |
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* unless first pattern char might match this text char. |
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*/ |
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if (ICHAREQ(t, p) || (*p == '\\') || (*p == '_')) |
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{ |
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int matched = MatchTextIC(t, tlen, p, plen); |
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if (matched != LIKE_FALSE) |
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return matched; /* TRUE or ABORT */ |
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} |
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NextChar(t, tlen); |
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} |
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/*
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* End of text with no match, so no point in trying later |
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* places to start matching this pattern. |
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*/ |
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return LIKE_ABORT; |
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} |
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else if ((*p != '_') && !ICHAREQ(t, p)) |
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{ |
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/*
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* Not the single-character wildcard and no explicit match? |
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* Then time to quit... |
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*/ |
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return LIKE_FALSE; |
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} |
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NextChar(t, tlen); |
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NextChar(p, plen); |
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} |
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if (tlen > 0) |
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return LIKE_FALSE; /* end of pattern, but not of text */ |
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/* End of input string. Do we have matching pattern remaining? */ |
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while ((plen > 0) && (*p == '%')) /* allow multiple %'s at end of
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* pattern */ |
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NextChar(p, plen); |
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if (plen <= 0) |
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return LIKE_TRUE; |
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/*
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* End of text with no match, so no point in trying later places to |
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* start matching this pattern. |
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*/ |
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return LIKE_ABORT; |
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} /* MatchTextIC() */ |
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/*
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* like_escape() --- given a pattern and an ESCAPE string, |
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* convert the pattern to use Postgres' standard backslash escape convention. |
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*/ |
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static text * |
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do_like_escape(text *pat, text *esc) |
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{ |
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text *result; |
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unsigned char *p, |
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*e, |
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*r; |
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int plen, |
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elen; |
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bool afterescape; |
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p = VARDATA(pat); |
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plen = (VARSIZE(pat) - VARHDRSZ); |
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e = VARDATA(esc); |
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elen = (VARSIZE(esc) - VARHDRSZ); |
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/*
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* Worst-case pattern growth is 2x --- unlikely, but it's hardly worth |
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* trying to calculate the size more accurately than that. |
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*/ |
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result = (text *) palloc(plen * 2 + VARHDRSZ); |
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r = VARDATA(result); |
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if (elen == 0) |
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{ |
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/*
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* No escape character is wanted. Double any backslashes in the |
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* pattern to make them act like ordinary characters. |
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*/ |
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while (plen > 0) |
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{ |
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if (*p == '\\') |
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*r++ = '\\'; |
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CopyAdvChar(r, p, plen); |
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} |
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} |
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else |
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{ |
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/*
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* The specified escape must be only a single character. |
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*/ |
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NextChar(e, elen); |
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if (elen != 0) |
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elog(ERROR, "ESCAPE string must be empty or one character"); |
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e = VARDATA(esc); |
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/*
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* If specified escape is '\', just copy the pattern as-is. |
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*/ |
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if (*e == '\\') |
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{ |
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memcpy(result, pat, VARSIZE(pat)); |
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return result; |
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} |
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/*
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* Otherwise, convert occurrences of the specified escape |
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* character to '\', and double occurrences of '\' --- unless they |
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* immediately follow an escape character! |
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*/ |
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afterescape = false; |
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while (plen > 0) |
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{ |
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if (CHAREQ(p, e) && !afterescape) |
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{ |
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*r++ = '\\'; |
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NextChar(p, plen); |
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afterescape = true; |
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} |
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else if (*p == '\\') |
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{ |
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*r++ = '\\'; |
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if (!afterescape) |
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*r++ = '\\'; |
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NextChar(p, plen); |
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afterescape = false; |
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} |
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else |
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{ |
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CopyAdvChar(r, p, plen); |
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afterescape = false; |
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} |
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} |
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} |
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VARATT_SIZEP(result) = r - ((unsigned char *) result); |
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return result; |
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} |
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