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cpython/Objects/stringlib/fastsearch.h at 3.5 · python/cpython · GitHub
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/* stringlib: fastsearch implementation */
#define
STRINGLIB_FASTSEARCH_H
/* 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/zone/stringlib.htm */
/* note: fastsearch may access s[n], which isn't a problem when using
Python's ordinary string types, but may cause problems if you're
using this code in other contexts. also, the count mode returns -1
if there cannot possible be a match in the target string, and 0 if
it has actually checked for matches, but didn't find any. callers
beware! */
#define
FAST_COUNT
0
#define
FAST_SEARCH
1
#define
FAST_RSEARCH
2
#if
LONG_BIT
>=
128
#define
STRINGLIB_BLOOM_WIDTH
128
#elif
LONG_BIT
>=
64
#define
STRINGLIB_BLOOM_WIDTH
64
#elif
LONG_BIT
>=
32
#define
STRINGLIB_BLOOM_WIDTH
32
#else
#error
"LONG_BIT is smaller than 32"
#endif
#define
STRINGLIB_BLOOM_ADD
(
mask
,
ch
) \
((mask |= (1UL << ((ch) & (STRINGLIB_BLOOM_WIDTH -1)))))
#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
,
int
mode
)
{
if
(
mode
==
FAST_SEARCH
) {
const
STRINGLIB_CHAR
*
ptr
=
s
;
const
STRINGLIB_CHAR
*
e
=
s
+
n
;
while
(
ptr
<
e
) {
void
*
candidate
=
memchr
((
const
void
*
)
ptr
,
needle
, (
e
-
ptr
)
*
sizeof
(
STRINGLIB_CHAR
));
if
(
candidate
==
NULL
)
return
-1
;
ptr
=
(
const
STRINGLIB_CHAR
*
)
_Py_ALIGN_DOWN
(
candidate
,
sizeof
(
STRINGLIB_CHAR
));
if
(
sizeof
(
STRINGLIB_CHAR
)
==
1
||
*
ptr
==
ch
)
return
(
ptr
-
s
);
/* False positive */
ptr
++
;
}
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
) {
const
STRINGLIB_CHAR
*
found
;
void
*
candidate
=
memrchr
((
const
void
*
)
s
,
needle
,
n
*
sizeof
(
STRINGLIB_CHAR
));
if
(
candidate
==
NULL
)
return
-1
;
found
=
(
const
STRINGLIB_CHAR
*
)
_Py_ALIGN_DOWN
(
candidate
,
sizeof
(
STRINGLIB_CHAR
));
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
,
Py_ssize_t
maxcount
,
int
mode
)
{
unsigned long
mask
;
Py_ssize_t
skip
,
count
=
0
;
Py_ssize_t
i
,
j
,
mlast
,
w
;
w
=
n
-
m
;
if
(
w
<
0
||
(
mode
==
FAST_COUNT
&&
maxcount
==
0
))
return
-1
;
/* look for special cases */
if
(
m
<=
1
) {
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
;
needle
=
p
[
0
]
&
0xff
;
#if
STRINGLIB_SIZEOF_CHAR
>
1
/* If looking for a multiple of 256, we'd have too
many false positives looking for the '\0' byte in UCS2
and UCS4 representations. */
if
(
needle
!=
0
)
#endif
return
STRINGLIB
(
fastsearch_memchr_1char
)
(
s
,
n
,
p
[
0
],
needle
,
mode
);
}
if
(
mode
==
FAST_COUNT
) {
for
(
i
=
0
;
i
<
n
;
i
++
)
if
(
s
[
i
]
==
p
[
0
]) {
count
++
;
if
(
count
==
maxcount
)
return
maxcount
;
}
return
count
;
}
else
if
(
mode
==
FAST_SEARCH
) {
for
(
i
=
0
;
i
<
n
;
i
++
)
if
(
s
[
i
]
==
p
[
0
])
return
i
;
}
else
{
/* FAST_RSEARCH */
for
(
i
=
n
-
1
;
i
>
-1
;
i
--
)
if
(
s
[
i
]
==
p
[
0
])
return
i
;
}
return
-1
;
}
mlast
=
m
-
1
;
skip
=
mlast
-
1
;
mask
=
0
;
if
(
mode
!=
FAST_RSEARCH
) {
const
STRINGLIB_CHAR
*
ss
=
s
+
m
-
1
;
const
STRINGLIB_CHAR
*
pp
=
p
+
m
-
1
;
/* create compressed boyer-moore delta 1 table */
/* process pattern[:-1] */
for
(
i
=
0
;
i
<
mlast
;
i
++
) {
STRINGLIB_BLOOM_ADD
(
mask
,
p
[
i
]);
if
(
p
[
i
]
==
p
[
mlast
])
skip
=
mlast
-
i
-
1
;
}
/* process pattern[-1] outside the loop */
STRINGLIB_BLOOM_ADD
(
mask
,
p
[
mlast
]);
for
(
i
=
0
;
i
<=
w
;
i
++
) {
/* note: using mlast in the skip path slows things down on x86 */
if
(
ss
[
i
]
==
pp
[
0
]) {
/* 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
++
;
if
(
count
==
maxcount
)
return
maxcount
;
i
=
i
+
mlast
;
continue
;
}
/* miss: check if next character is part of pattern */
if
(!
STRINGLIB_BLOOM
(
mask
,
ss
[
i
+
1
]))
i
=
i
+
m
;
else
i
=
i
+
skip
;
}
else
{
/* skip: check if next character is part of pattern */
if
(!
STRINGLIB_BLOOM
(
mask
,
ss
[
i
+
1
]))
i
=
i
+
m
;
}
}
}
else
{
/* FAST_RSEARCH */
/* create compressed boyer-moore delta 1 table */
/* process pattern[0] outside the loop */
STRINGLIB_BLOOM_ADD
(
mask
,
p
[
0
]);
/* process pattern[:0:-1] */
for
(
i
=
mlast
;
i
>
0
;
i
--
) {
STRINGLIB_BLOOM_ADD
(
mask
,
p
[
i
]);
if
(
p
[
i
]
==
p
[
0
])
skip
=
i
-
1
;
}
for
(
i
=
w
;
i
>=
0
;
i
--
) {
if
(
s
[
i
]
==
p
[
0
]) {
/* candidate match */
for
(
j
=
mlast
;
j
>
0
;
j
--
)
if
(
s
[
i
+
j
]
!=
p
[
j
])
break
;
if
(
j
==
0
)
/* got a match! */
return
i
;
/* miss: check if previous character is part of pattern */
if
(
i
>
0
&&
!
STRINGLIB_BLOOM
(
mask
,
s
[
i
-
1
]))
i
=
i
-
m
;
else
i
=
i
-
skip
;
}
else
{
/* skip: check if previous character is part of pattern */
if
(
i
>
0
&&
!
STRINGLIB_BLOOM
(
mask
,
s
[
i
-
1
]))
i
=
i
-
m
;
}
}
}
if
(
mode
!=
FAST_COUNT
)
return
-1
;
return
count
;
}
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