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substring split now uses /F's fast string matching algorithm.

Browse source 
(If compiled without FAST search support, changed the pre-memcmp test
   to check the last character as well as the first.  This gave a 25%
   speedup for my test case.)

Rewrote the split algorithms so they stop when maxsplit gets to 0.
Previously they did a string match first then checked if the maxsplit
was reached.  The new way prevents a needless string search.
This commit is contained in:
Andrew Dalke 2006-05-26 19:02:09 +00:00
parent afe6598732
commit c5da53ba78
1 changed files with 59 additions and 42 deletions
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101
Objects/stringobject.c
View file

@ -1322,6 +1322,13 @@ static const char *stripformat[] = {"|O:lstrip", "|O:rstrip", "|O:strip"};
#define STRIPNAME(i) (stripformat[i]+3)
/* Don't call if length < 2 */
#define Py_STRING_MATCH(target, offset, pattern, length) \
(target[offset] == pattern[0] && \
target[offset+length-1] == pattern[length-1] && \
!memcmp(target+offset+1, pattern+1, length-2) )
/* Overallocate the initial list to reduce the number of reallocs for small
split sizes. Eg, "A A A A A A A A A A".split() (10 elements) has three
resizes, to sizes 4, 8, then 16. Most observed string splits are for human
@ -1416,18 +1423,19 @@ split_char(const char *s, Py_ssize_t len, char ch, Py_ssize_t maxcount)
if (list == NULL)
return NULL;
for (i = j = 0; i < len; ) {
/* TODO: Use findchar/memchr for this? */
if (s[i] == ch) {
if (maxcount-- <= 0)
i = j = 0;
while ((j < len) && (maxcount-- > 0)) {
for(; j<len; j++) {
/* I found that using memchr makes no difference */
if (s[j] == ch) {
SPLIT_ADD(s, i, j);
i = j = j + 1;
break;
SPLIT_ADD(s, j, i);
i = j = i + 1;
} else
i++;
}
}
}
if (j <= len) {
SPLIT_ADD(s, j, len);
if (i <= len) {
SPLIT_ADD(s, i, len);
}
FIX_PREALLOC_SIZE(list);
return list;
@ -1452,6 +1460,9 @@ string_split(PyStringObject *self, PyObject *args)
Py_ssize_t maxsplit = -1, count=0;
const char *s = PyString_AS_STRING(self), *sub;
PyObject *list, *str, *subobj = Py_None;
#ifdef USE_FAST
Py_ssize_t pos;
#endif
if (!PyArg_ParseTuple(args, "|On:split", &subobj, &maxsplit))
return NULL;
@ -1481,19 +1492,30 @@ string_split(PyStringObject *self, PyObject *args)
if (list == NULL)
return NULL;
#ifdef USE_FAST
i = j = 0;
while (i+n <= len) {
/* TODO: Use Py_STRING_MATCH */
if (s[i] == sub[0] && memcmp(s+i, sub, n) == 0) {
if (maxsplit-- <= 0)
break;
SPLIT_ADD(s, j, i);
i = j = i + n;
}
else
i++;
while (maxsplit-- > 0) {
pos = fastsearch(s+i, len-i, sub, n, FAST_SEARCH);
if (pos < 0)
break;
j = i+pos;
SPLIT_ADD(s, i, j);
i = j + n;
}
SPLIT_ADD(s, j, len);
#else
i = j = 0;
while ((j+n <= len) && (maxsplit-- > 0)) {
for (; j+n <= len; j++) {
if (Py_STRING_MATCH(s, j, sub, n)) {
SPLIT_ADD(s, i, j);
i = j = j + n;
break;
}
}
}
#endif
SPLIT_ADD(s, i, len);
FIX_PREALLOC_SIZE(list);
return list;
@ -1610,14 +1632,15 @@ rsplit_char(const char *s, Py_ssize_t len, char ch, Py_ssize_t maxcount)
if (list == NULL)
return NULL;
for (i = j = len - 1; i >= 0; ) {
if (s[i] == ch) {
if (maxcount-- <= 0)
i = j = len - 1;
while ((i >= 0) && (maxcount-- > 0)) {
for (; i >= 0; i--) {
if (s[i] == ch) {
SPLIT_ADD(s, i + 1, j + 1);
j = i = i - 1;
break;
SPLIT_ADD(s, i + 1, j + 1);
j = i = i - 1;
} else
i--;
}
}
}
if (j >= -1) {
SPLIT_ADD(s, 0, j + 1);
@ -1679,16 +1702,16 @@ string_rsplit(PyStringObject *self, PyObject *args)
j = len;
i = j - n;
while (i >= 0) {
if (s[i] == sub[0] && memcmp(s+i, sub, n) == 0) {
if (maxsplit-- <= 0)
while ( (i >= 0) && (maxsplit-- > 0) ) {
for (; i>=0; i--) {
if (Py_STRING_MATCH(s, i, sub, n)) {
SPLIT_ADD(s, i + n, j);
j = i;
i -= n;
break;
SPLIT_ADD(s, i+n, j);
j = i;
i -= n;
}
}
else
i--;
}
SPLIT_ADD(s, 0, j);
FIX_PREALLOC_SIZE(list);
@ -2449,12 +2472,6 @@ string_translate(PyStringObject *self, PyObject *args)
/* find and count characters and substrings */
/* Don't call if length < 2 */
#define Py_STRING_MATCH(target, offset, pattern, length) \
(target[offset] == pattern[0] && \
target[offset+length-1] == pattern[length-1] && \
!memcmp(target+offset+1, pattern+1, length-2) )
#define findchar(target, target_len, c) \
((char *)memchr((const void *)(target), c, target_len))