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needforspeed: use "fastsearch" for count and findstring helpers. this 

results in a 2.5x speedup on the stringbench count tests, and a 20x (!)
speedup on the stringbench search/find/contains test, compared to 2.5a2.

for more on the algorithm, see:

    http://effbot.org/zone/stringlib.htm

if you get weird results, you can disable the new algoritm by undefining
USE_FAST in Objects/unicodeobject.c.

enjoy /F
This commit is contained in:
Fredrik Lundh 2006-05-24 14:28:11 +00:00
parent 240bf2a8e4
commit 6471ee4f18
1 changed files with 109 additions and 1 deletions
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110
Objects/unicodeobject.c
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@ -3848,7 +3848,94 @@ int PyUnicode_EncodeDecimal(Py_UNICODE *s,
/* --- Helpers ------------------------------------------------------------ */
static Py_ssize_t count(PyUnicodeObject *self,
#define USE_FAST /* experimental fast search implementation */
/* fast search/count implementation, based on a mix between boyer-
moore and horspool, with a few more bells and whistles on the top.
for some more background, see: http://effbot.org/stringlib */
#define FAST_COUNT 0
#define FAST_SEARCH 1
LOCAL(int) fastsearch(Py_UNICODE* s, Py_ssize_t n,
Py_UNICODE* p, Py_ssize_t m,
int mode)
{
long mask;
int skip, count = 0;
Py_ssize_t i, j, mlast, w;
w = n - m;
if (w < 0)
return -1;
/* look for special cases */
if (m <= 1) {
if (m < 0)
return -1;
/* use special case for 1-character strings */
if (mode == FAST_COUNT) {
for (i = 0; i < n; i++)
if (s[i] == p[0])
count++;
return count;
} else {
for (i = 0; i < n; i++)
if (s[i] == p[0])
return i;
}
return -1;
}
mlast = m - 1;
/* create compressed boyer-moore delta 1 table */
skip = mlast - 1;
/* process pattern[:-1] */
for (mask = i = 0; i < mlast; i++) {
mask |= (1 << (p[i] & 0x1F));
if (p[i] == p[mlast])
skip = mlast - i - 1;
}
/* process pattern[-1] outside the loop */
mask |= (1 << (p[mlast] & 0x1F));
for (i = 0; i <= w; i++) {
/* note: using mlast in the skip path slows things down on x86 */
if (s[i+m-1] == p[m-1]) {
/* candidate match */
for (j = 0; j < mlast; j++)
if (s[i+j] != p[j])
break;
if (j == mlast) {
/* got a match! */
if (mode != FAST_COUNT)
return i;
count++;
i = i + mlast;
continue;
}
/* miss: check if next character is part of pattern */
if (!(mask & (1 << (s[i+m] & 0x1F))))
i = i + m;
else {
i = i + skip;
continue;
}
} else {
/* skip: check if next character is part of pattern */
if (!(mask & (1 << (s[i+m] & 0x1F))))
i = i + m;
}
}
if (mode != FAST_COUNT)
return -1;
return count;
}
LOCAL(Py_ssize_t) count(PyUnicodeObject *self,
Py_ssize_t start,
Py_ssize_t end,
PyUnicodeObject *substring)
@ -3869,6 +3956,14 @@ static Py_ssize_t count(PyUnicodeObject *self,
if (substring->length == 0)
return (end - start + 1);
#ifdef USE_FAST
count = fastsearch(
PyUnicode_AS_UNICODE(self) + start, end - start,
substring->str, substring->length, FAST_COUNT
);
if (count < 0)
count = 0; /* no match */
#else
end -= substring->length;
while (start <= end)
@ -3877,6 +3972,7 @@ static Py_ssize_t count(PyUnicodeObject *self,
start += substring->length;
} else
start++;
#endif
return count;
}
@ -3927,6 +4023,18 @@ static Py_ssize_t findstring(PyUnicodeObject *self,
if (substring->length == 0)
return (direction > 0) ? start : end;
#ifdef USE_FAST
if (direction > 0) {
Py_ssize_t pos = fastsearch(
PyUnicode_AS_UNICODE(self) + start, end - start,
substring->str, substring->length, FAST_SEARCH
);
if (pos < 0)
return pos;
return pos + start;
}
#endif
end -= substring->length;
if (direction < 0) {