diff options
Diffstat (limited to 'src/search.c')
| -rw-r--r-- | src/search.c | 167 |
1 files changed, 69 insertions, 98 deletions
diff --git a/src/search.c b/src/search.c index 39c130ba70f..2eb435276a3 100644 --- a/src/search.c +++ b/src/search.c @@ -1729,9 +1729,8 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, { int direction = ((n > 0) ? 1 : -1); register int dirlen; - int infinity, limit, stride_for_teases = 0; - register int *BM_tab; - int *BM_tab_base; + int limit, stride_for_teases = 0; + int BM_tab[0400]; register unsigned char *cursor, *p_limit; register int i, j; unsigned char *pat, *pat_end; @@ -1747,37 +1746,28 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, int translate_prev_byte3 = 0; int translate_prev_byte4 = 0; - BM_tab = (int *) alloca (0400 * sizeof (int)); - - /* The general approach is that we are going to maintain that we know */ - /* the first (closest to the present position, in whatever direction */ - /* we're searching) character that could possibly be the last */ - /* (furthest from present position) character of a valid match. We */ - /* advance the state of our knowledge by looking at that character */ - /* and seeing whether it indeed matches the last character of the */ - /* pattern. If it does, we take a closer look. If it does not, we */ - /* move our pointer (to putative last characters) as far as is */ - /* logically possible. This amount of movement, which I call a */ - /* stride, will be the length of the pattern if the actual character */ - /* appears nowhere in the pattern, otherwise it will be the distance */ - /* from the last occurrence of that character to the end of the */ - /* pattern. */ - /* As a coding trick, an enormous stride is coded into the table for */ - /* characters that match the last character. This allows use of only */ - /* a single test, a test for having gone past the end of the */ - /* permissible match region, to test for both possible matches (when */ - /* the stride goes past the end immediately) and failure to */ - /* match (where you get nudged past the end one stride at a time). */ - - /* Here we make a "mickey mouse" BM table. The stride of the search */ - /* is determined only by the last character of the putative match. */ - /* If that character does not match, we will stride the proper */ - /* distance to propose a match that superimposes it on the last */ - /* instance of a character that matches it (per trt), or misses */ - /* it entirely if there is none. */ + /* The general approach is that we are going to maintain that we know + the first (closest to the present position, in whatever direction + we're searching) character that could possibly be the last + (furthest from present position) character of a valid match. We + advance the state of our knowledge by looking at that character + and seeing whether it indeed matches the last character of the + pattern. If it does, we take a closer look. If it does not, we + move our pointer (to putative last characters) as far as is + logically possible. This amount of movement, which I call a + stride, will be the length of the pattern if the actual character + appears nowhere in the pattern, otherwise it will be the distance + from the last occurrence of that character to the end of the + pattern. If the amount is zero we have a possible match. */ + + /* Here we make a "mickey mouse" BM table. The stride of the search + is determined only by the last character of the putative match. + If that character does not match, we will stride the proper + distance to propose a match that superimposes it on the last + instance of a character that matches it (per trt), or misses + it entirely if there is none. */ dirlen = len_byte * direction; - infinity = dirlen - (lim_byte + pos_byte + len_byte + len_byte) * direction; /* Record position after the end of the pattern. */ pat_end = base_pat + len_byte; @@ -1787,23 +1777,14 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, if (direction < 0) base_pat = pat_end - 1; - BM_tab_base = BM_tab; - BM_tab += 0400; - j = dirlen; /* to get it in a register */ - /* A character that does not appear in the pattern induces a */ - /* stride equal to the pattern length. */ - while (BM_tab_base != BM_tab) - { - *--BM_tab = j; - *--BM_tab = j; - *--BM_tab = j; - *--BM_tab = j; - } + /* A character that does not appear in the pattern induces a + stride equal to the pattern length. */ + for (i = 0; i < 0400; i++) + BM_tab[i] = dirlen; /* We use this for translation, instead of TRT itself. We fill this in to handle the characters that actually occur in the pattern. Others don't matter anyway! */ - bzero (simple_translate, sizeof simple_translate); for (i = 0; i < 0400; i++) simple_translate[i] = i; @@ -1828,12 +1809,10 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, } i = 0; - while (i != infinity) + while (i != dirlen) { unsigned char *ptr = base_pat + i; i += direction; - if (i == dirlen) - i = infinity; if (! NILP (trt)) { /* If the byte currently looking at is the last of a @@ -1861,7 +1840,7 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, else j = *ptr; - if (i == infinity) + if (i == dirlen) stride_for_teases = BM_tab[j]; BM_tab[j] = dirlen - i; @@ -1894,17 +1873,16 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, { j = *ptr; - if (i == infinity) + if (i == dirlen) stride_for_teases = BM_tab[j]; BM_tab[j] = dirlen - i; } - /* stride_for_teases tells how much to stride if we get a */ - /* match on the far character but are subsequently */ - /* disappointed, by recording what the stride would have been */ - /* for that character if the last character had been */ - /* different. */ + /* stride_for_teases tells how much to stride if we get a + match on the far character but are subsequently + disappointed, by recording what the stride would have been + for that character if the last character had been + different. */ } - infinity = dirlen - infinity; pos_byte += dirlen - ((direction > 0) ? direction : 0); /* loop invariant - POS_BYTE points at where last char (first char if reverse) of pattern would align in a possible match. */ @@ -1948,43 +1926,34 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, p_limit = BYTE_POS_ADDR (limit); p2 = (cursor = BYTE_POS_ADDR (pos_byte)); - /* In this loop, pos + cursor - p2 is the surrogate for pos */ + /* In this loop, pos + cursor - p2 is the surrogate for pos. */ while (1) /* use one cursor setting as long as i can */ { if (direction > 0) /* worth duplicating */ { - /* Use signed comparison if appropriate - to make cursor+infinity sure to be > p_limit. - Assuming that the buffer lies in a range of addresses - that are all "positive" (as ints) or all "negative", - either kind of comparison will work as long - as we don't step by infinity. So pick the kind - that works when we do step by infinity. */ - if ((EMACS_INT) (p_limit + infinity) > (EMACS_INT) p_limit) - while ((EMACS_INT) cursor <= (EMACS_INT) p_limit) - cursor += BM_tab[*cursor]; - else - while ((EMACS_UINT) cursor <= (EMACS_UINT) p_limit) + while (cursor <= p_limit) + { + if (BM_tab[*cursor] == 0) + goto hit; cursor += BM_tab[*cursor]; + } } else { - if ((EMACS_INT) (p_limit + infinity) < (EMACS_INT) p_limit) - while ((EMACS_INT) cursor >= (EMACS_INT) p_limit) - cursor += BM_tab[*cursor]; - else - while ((EMACS_UINT) cursor >= (EMACS_UINT) p_limit) + while (cursor >= p_limit) + { + if (BM_tab[*cursor] == 0) + goto hit; cursor += BM_tab[*cursor]; + } } -/* If you are here, cursor is beyond the end of the searched region. */ -/* This can happen if you match on the far character of the pattern, */ -/* because the "stride" of that character is infinity, a number able */ -/* to throw you well beyond the end of the search. It can also */ -/* happen if you fail to match within the permitted region and would */ -/* otherwise try a character beyond that region */ - if ((cursor - p_limit) * direction <= len_byte) - break; /* a small overrun is genuine */ - cursor -= infinity; /* large overrun = hit */ + /* If you are here, cursor is beyond the end of the + searched region. You fail to match within the + permitted region and would otherwise try a character + beyond that region. */ + break; + + hit: i = dirlen - direction; if (! NILP (trt)) { @@ -2056,8 +2025,8 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, pos_byte += cursor - p2; } else - /* Now we'll pick up a clump that has to be done the hard */ - /* way because it covers a discontinuity */ + /* Now we'll pick up a clump that has to be done the hard + way because it covers a discontinuity. */ { limit = ((direction > 0) ? BUFFER_CEILING_OF (pos_byte - dirlen + 1) @@ -2069,19 +2038,21 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, and still be valid for a possible match. */ while (1) { - /* This loop can be coded for space rather than */ - /* speed because it will usually run only once. */ - /* (the reach is at most len + 21, and typically */ - /* does not exceed len) */ + /* This loop can be coded for space rather than + speed because it will usually run only once. + (the reach is at most len + 21, and typically + does not exceed len). */ while ((limit - pos_byte) * direction >= 0) - pos_byte += BM_tab[FETCH_BYTE (pos_byte)]; - /* now run the same tests to distinguish going off the */ - /* end, a match or a phony match. */ - if ((pos_byte - limit) * direction <= len_byte) - break; /* ran off the end */ - /* Found what might be a match. - Set POS_BYTE back to last (first if reverse) pos. */ - pos_byte -= infinity; + { + int ch = FETCH_BYTE (pos_byte); + if (BM_tab[ch] == 0) + goto hit2; + pos_byte += BM_tab[ch]; + } + break; /* ran off the end */ + + hit2: + /* Found what might be a match. */ i = dirlen - direction; while ((i -= direction) + direction != 0) { @@ -2110,7 +2081,7 @@ boyer_moore (n, base_pat, len, len_byte, trt, inverse_trt, /* Above loop has moved POS_BYTE part or all the way back to the first pos (last pos if reverse). Set it once again at the last (first if reverse) char. */ - pos_byte += dirlen - i- direction; + pos_byte += dirlen - i - direction; if (i + direction == 0) { int position, start, end; |