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7efa3b8242
efficient machine code. Patch written by Antoine Pitrou. Without this change, str.find() was 10% slower than str.rfind() in the worst case.
227 lines
7.2 KiB
C
227 lines
7.2 KiB
C
/* stringlib: fastsearch implementation */
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#define STRINGLIB_FASTSEARCH_H
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/* fast search/count implementation, based on a mix between boyer-
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moore and horspool, with a few more bells and whistles on the top.
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for some more background, see: http://effbot.org/zone/stringlib.htm */
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/* note: fastsearch may access s[n], which isn't a problem when using
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Python's ordinary string types, but may cause problems if you're
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using this code in other contexts. also, the count mode returns -1
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if there cannot possible be a match in the target string, and 0 if
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it has actually checked for matches, but didn't find any. callers
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beware! */
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#define FAST_COUNT 0
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#define FAST_SEARCH 1
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#define FAST_RSEARCH 2
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#if LONG_BIT >= 128
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#define STRINGLIB_BLOOM_WIDTH 128
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#elif LONG_BIT >= 64
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#define STRINGLIB_BLOOM_WIDTH 64
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#elif LONG_BIT >= 32
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#define STRINGLIB_BLOOM_WIDTH 32
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#else
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#error "LONG_BIT is smaller than 32"
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#endif
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#define STRINGLIB_BLOOM_ADD(mask, ch) \
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((mask |= (1UL << ((ch) & (STRINGLIB_BLOOM_WIDTH -1)))))
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#define STRINGLIB_BLOOM(mask, ch) \
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((mask & (1UL << ((ch) & (STRINGLIB_BLOOM_WIDTH -1)))))
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Py_LOCAL_INLINE(Py_ssize_t)
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STRINGLIB(fastsearch_memchr_1char)(const STRINGLIB_CHAR* s, Py_ssize_t n,
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STRINGLIB_CHAR ch, unsigned char needle,
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Py_ssize_t maxcount, int mode)
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{
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if (mode == FAST_SEARCH) {
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const STRINGLIB_CHAR *ptr = s;
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const STRINGLIB_CHAR *e = s + n;
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while (ptr < e) {
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void *candidate = memchr((const void *) ptr, needle, (e - ptr) * sizeof(STRINGLIB_CHAR));
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if (candidate == NULL)
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return -1;
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ptr = (const STRINGLIB_CHAR *) _Py_ALIGN_DOWN(candidate, sizeof(STRINGLIB_CHAR));
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if (sizeof(STRINGLIB_CHAR) == 1 || *ptr == ch)
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return (ptr - s);
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/* False positive */
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ptr++;
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}
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return -1;
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}
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#ifdef HAVE_MEMRCHR
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/* memrchr() is a GNU extension, available since glibc 2.1.91.
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it doesn't seem as optimized as memchr(), but is still quite
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faster than our hand-written loop in FASTSEARCH below */
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else if (mode == FAST_RSEARCH) {
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while (n > 0) {
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const STRINGLIB_CHAR *found;
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void *candidate = memrchr((const void *) s, needle, n * sizeof(STRINGLIB_CHAR));
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if (candidate == NULL)
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return -1;
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found = (const STRINGLIB_CHAR *) _Py_ALIGN_DOWN(candidate, sizeof(STRINGLIB_CHAR));
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n = found - s;
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if (sizeof(STRINGLIB_CHAR) == 1 || *found == ch)
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return n;
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/* False positive */
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}
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return -1;
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}
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#endif
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else {
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assert(0); /* Should never get here */
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return 0;
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}
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#undef DO_MEMCHR
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}
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Py_LOCAL_INLINE(Py_ssize_t)
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FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n,
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const STRINGLIB_CHAR* p, Py_ssize_t m,
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Py_ssize_t maxcount, int mode)
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{
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unsigned long mask;
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Py_ssize_t skip, count = 0;
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Py_ssize_t i, j, mlast, w;
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w = n - m;
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if (w < 0 || (mode == FAST_COUNT && maxcount == 0))
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return -1;
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/* look for special cases */
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if (m <= 1) {
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if (m <= 0)
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return -1;
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/* use special case for 1-character strings */
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if (n > 10 && (mode == FAST_SEARCH
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#ifdef HAVE_MEMRCHR
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|| mode == FAST_RSEARCH
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#endif
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)) {
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/* use memchr if we can choose a needle without two many likely
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false positives */
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unsigned char needle;
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needle = p[0] & 0xff;
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#if STRINGLIB_SIZEOF_CHAR > 1
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/* If looking for a multiple of 256, we'd have too
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many false positives looking for the '\0' byte in UCS2
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and UCS4 representations. */
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if (needle != 0)
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#endif
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return STRINGLIB(fastsearch_memchr_1char)
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(s, n, p[0], needle, maxcount, mode);
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}
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if (mode == FAST_COUNT) {
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for (i = 0; i < n; i++)
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if (s[i] == p[0]) {
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count++;
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if (count == maxcount)
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return maxcount;
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}
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return count;
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} else if (mode == FAST_SEARCH) {
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for (i = 0; i < n; i++)
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if (s[i] == p[0])
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return i;
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} else { /* FAST_RSEARCH */
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for (i = n - 1; i > -1; i--)
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if (s[i] == p[0])
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return i;
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}
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return -1;
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}
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mlast = m - 1;
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skip = mlast - 1;
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mask = 0;
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if (mode != FAST_RSEARCH) {
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const STRINGLIB_CHAR *ss = s + m - 1;
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const STRINGLIB_CHAR *pp = p + m - 1;
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/* create compressed boyer-moore delta 1 table */
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/* process pattern[:-1] */
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for (i = 0; i < mlast; i++) {
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STRINGLIB_BLOOM_ADD(mask, p[i]);
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if (p[i] == p[mlast])
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skip = mlast - i - 1;
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}
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/* process pattern[-1] outside the loop */
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STRINGLIB_BLOOM_ADD(mask, p[mlast]);
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for (i = 0; i <= w; i++) {
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/* note: using mlast in the skip path slows things down on x86 */
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if (ss[i] == pp[0]) {
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/* candidate match */
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for (j = 0; j < mlast; j++)
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if (s[i+j] != p[j])
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break;
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if (j == mlast) {
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/* got a match! */
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if (mode != FAST_COUNT)
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return i;
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count++;
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if (count == maxcount)
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return maxcount;
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i = i + mlast;
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continue;
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}
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/* miss: check if next character is part of pattern */
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if (!STRINGLIB_BLOOM(mask, ss[i+1]))
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i = i + m;
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else
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i = i + skip;
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} else {
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/* skip: check if next character is part of pattern */
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if (!STRINGLIB_BLOOM(mask, ss[i+1]))
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i = i + m;
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}
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}
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} else { /* FAST_RSEARCH */
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/* create compressed boyer-moore delta 1 table */
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/* process pattern[0] outside the loop */
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STRINGLIB_BLOOM_ADD(mask, p[0]);
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/* process pattern[:0:-1] */
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for (i = mlast; i > 0; i--) {
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STRINGLIB_BLOOM_ADD(mask, p[i]);
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if (p[i] == p[0])
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skip = i - 1;
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}
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for (i = w; i >= 0; i--) {
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if (s[i] == p[0]) {
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/* candidate match */
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for (j = mlast; j > 0; j--)
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if (s[i+j] != p[j])
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break;
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if (j == 0)
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/* got a match! */
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return i;
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/* miss: check if previous character is part of pattern */
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if (i > 0 && !STRINGLIB_BLOOM(mask, s[i-1]))
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i = i - m;
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else
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i = i - skip;
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} else {
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/* skip: check if previous character is part of pattern */
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if (i > 0 && !STRINGLIB_BLOOM(mask, s[i-1]))
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i = i - m;
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}
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}
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}
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if (mode != FAST_COUNT)
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return -1;
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return count;
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}
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