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author | Antoine Pitrou <solipsis@pitrou.net> | 2011-10-11 18:29:21 (GMT) |
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committer | Antoine Pitrou <solipsis@pitrou.net> | 2011-10-11 18:29:21 (GMT) |
commit | 2c3b2302adb1bb00b6050afc30eacbc023379b93 (patch) | |
tree | c41e4702224848fd137a0e6043949d1fa88b3b77 /Objects/stringlib | |
parent | 60dd7dc23c37bbb1c6ecc83a866f1a379afce443 (diff) | |
download | cpython-2c3b2302adb1bb00b6050afc30eacbc023379b93.zip cpython-2c3b2302adb1bb00b6050afc30eacbc023379b93.tar.gz cpython-2c3b2302adb1bb00b6050afc30eacbc023379b93.tar.bz2 |
Issue #13134: optimize finding single-character strings using memchr
Diffstat (limited to 'Objects/stringlib')
-rw-r--r-- | Objects/stringlib/fastsearch.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/Objects/stringlib/fastsearch.h b/Objects/stringlib/fastsearch.h index d35cba3..33ab6ff 100644 --- a/Objects/stringlib/fastsearch.h +++ b/Objects/stringlib/fastsearch.h @@ -32,6 +32,60 @@ #define STRINGLIB_BLOOM(mask, ch) \ ((mask & (1UL << ((ch) & (STRINGLIB_BLOOM_WIDTH -1))))) + +Py_LOCAL_INLINE(Py_ssize_t) +STRINGLIB(fastsearch_memchr_1char)(const STRINGLIB_CHAR* s, Py_ssize_t n, + STRINGLIB_CHAR ch, unsigned char needle, + Py_ssize_t maxcount, int mode) +{ + void *candidate; + const STRINGLIB_CHAR *found; + +#define DO_MEMCHR(memchr, s, needle, nchars) do { \ + candidate = memchr((const void *) (s), (needle), (nchars) * sizeof(STRINGLIB_CHAR)); \ + found = (const STRINGLIB_CHAR *) \ + ((Py_ssize_t) candidate & (~ ((Py_ssize_t) sizeof(STRINGLIB_CHAR) - 1))); \ + } while (0) + + if (mode == FAST_SEARCH) { + const STRINGLIB_CHAR *_s = s; + const STRINGLIB_CHAR *e = s + n; + while (_s < e) { + DO_MEMCHR(memchr, _s, needle, e - _s); + if (found == NULL) + return -1; + if (sizeof(STRINGLIB_CHAR) == 1 || *found == ch) + return (found - _s); + /* False positive */ + _s = found + 1; + } + return -1; + } +#ifdef HAVE_MEMRCHR + /* memrchr() is a GNU extension, available since glibc 2.1.91. + it doesn't seem as optimized as memchr(), but is still quite + faster than our hand-written loop in FASTSEARCH below */ + else if (mode == FAST_RSEARCH) { + while (n > 0) { + DO_MEMCHR(memrchr, s, needle, n); + if (found == NULL) + return -1; + n = found - s; + if (sizeof(STRINGLIB_CHAR) == 1 || *found == ch) + return n; + /* False positive */ + } + return -1; + } +#endif + else { + assert(0); /* Should never get here */ + return 0; + } + +#undef DO_MEMCHR +} + Py_LOCAL_INLINE(Py_ssize_t) FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n, const STRINGLIB_CHAR* p, Py_ssize_t m, @@ -51,6 +105,25 @@ FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n, if (m <= 0) return -1; /* use special case for 1-character strings */ + if (n > 10 && (mode == FAST_SEARCH +#ifdef HAVE_MEMRCHR + || mode == FAST_RSEARCH +#endif + )) { + /* use memchr if we can choose a needle without two many likely + false positives */ + unsigned char needle; + int use_needle = 1; + needle = p[0] & 0xff; + if (needle == 0 && sizeof(STRINGLIB_CHAR) > 1) { + needle = (p[0] >> 8) & 0xff; + if (needle >= 32) + use_needle = 0; + } + if (use_needle) + return STRINGLIB(fastsearch_memchr_1char) + (s, n, p[0], needle, maxcount, mode); + } if (mode == FAST_COUNT) { for (i = 0; i < n; i++) if (s[i] == p[0]) { |