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Make strstr and strcasestr O(n), not O(n^2); add memmem. 

* libc/string/str-two-way.h: New file.
* libc/string/memmem.c (memmem): New file.
* libc/include/string.h (memmem): Declare for all platforms.
* libc/string/strstr.c (strstr): Provide O(n) implementation when
not optimizing for space.
* libc/string/strcasestr.c (strcasestr): Likewise.
* libc/string/Makefile.am (ELIX_SOURCES): Rename to...
(ELIX_2_SOURCES): ...this.
(ELIX_4_SOURCES): New category, for memmem.
(lib_a_SOURCES, libstring_la_SOURCES): Build new file.
(CHEWOUT_FILES): Build documentation for memmem.
* libc/string/strings.tex: Include new docs.
This commit is contained in:
Eric Blake 2008-01-12 04:25:55 +00:00
parent 978e84cf60
commit 40617efc8b
8 changed files with 664 additions and 16 deletions
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16
newlib/ChangeLog
View File

@ -1,3 +1,19 @@
2008-01-11 Eric Blake <ebb9@byu.net>
Make strstr and strcasestr O(n), not O(n^2); add memmem.
* libc/string/str-two-way.h: New file.
* libc/string/memmem.c (memmem): New file.
* libc/include/string.h (memmem): Declare for all platforms.
* libc/string/strstr.c (strstr): Provide O(n) implementation when
not optimizing for space.
* libc/string/strcasestr.c (strcasestr): Likewise.
* libc/string/Makefile.am (ELIX_SOURCES): Rename to...
(ELIX_2_SOURCES): ...this.
(ELIX_4_SOURCES): New category, for memmem.
(lib_a_SOURCES, libstring_la_SOURCES): Build new file.
(CHEWOUT_FILES): Build documentation for memmem.
* libc/string/strings.tex: Include new docs.
2008-01-08 Jeff Johnston <jjohnstn@redhat.com>
* libc/machine/m68k/memcpy.S: Remove % from register references

4
newlib/libc/include/string.h
View File

@ -56,9 +56,7 @@ int _EXFUN(ffs,(int));
char *_EXFUN(index,(const char *, int));
_PTR _EXFUN(memccpy,(_PTR, const _PTR, int, size_t));
_PTR _EXFUN(mempcpy,(_PTR, const _PTR, size_t));
#ifdef __CYGWIN__
extern void *memmem (__const void *, size_t, __const void *, size_t);
#endif
_PTR _EXFUN(memmem, (const _PTR, size_t, const _PTR, size_t));
char *_EXFUN(rindex,(const char *, int));
char *_EXFUN(stpcpy,(char *, const char *));
char *_EXFUN(stpncpy,(char *, const char *, size_t));

26
newlib/libc/string/Makefile.am
View File

@ -72,9 +72,9 @@ GENERAL_SOURCES = \
wmemset.c
if ELIX_LEVEL_1
ELIX_SOURCES =
ELIX_2_SOURCES =
else
ELIX_SOURCES = \
ELIX_2_SOURCES = \
bcmp.c \
memccpy.c \
mempcpy.c \
@ -87,15 +87,30 @@ ELIX_SOURCES = \
wcpncpy.c \
endif
if ELIX_LEVEL_1
ELIX_4_SOURCES =
else
if ELIX_LEVEL_2
ELIX_4_SOURCES =
else
if ELIX_LEVEL_3
ELIX_4_SOURCES =
else
ELIX_4_SOURCES = \
memmem.c
endif !ELIX_LEVEL_3
endif !ELIX_LEVEL_2
endif !ELIX_LEVEL_1
libstring_la_LDFLAGS = -Xcompiler -nostdlib
if USE_LIBTOOL
noinst_LTLIBRARIES = libstring.la
libstring_la_SOURCES = $(GENERAL_SOURCES) $(ELIX_SOURCES)
libstring_la_SOURCES = $(GENERAL_SOURCES) $(ELIX_2_SOURCES) $(ELIX_4_SOURCES)
noinst_DATA = objectlist.awk.in
else
noinst_LIBRARIES = lib.a
lib_a_SOURCES = $(GENERAL_SOURCES) $(ELIX_SOURCES)
lib_a_SOURCES = $(GENERAL_SOURCES) $(ELIX_2_SOURCES) $(ELIX_4_SOURCES)
lib_a_CFLAGS = $(AM_CFLAGS)
noinst_DATA =
endif # USE_LIBTOOL
@ -117,7 +132,8 @@ wcslcat.def wcslcpy.def wcslen.def wcsncat.def \
wcsncmp.def wcsncpy.def wcsnlen.def wcspbrk.def \
wcsrchr.def wcsspn.def wcsstr.def \
wcswidth.def wcsxfrm.def wcwidth.def wmemchr.def \
wmemcmp.def wmemcpy.def wmemmove.def wmemset.def
wmemcmp.def wmemcpy.def wmemmove.def wmemset.def \
memmem.def
SUFFIXES = .def

102
newlib/libc/string/memmem.c Normal file
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@ -0,0 +1,102 @@
/* Byte-wise substring search, using the Two-Way algorithm.
* Copyright (C) 2008 Eric Blake
* Permission to use, copy, modify, and distribute this software
* is freely granted, provided that this notice is preserved.
*/
/*
FUNCTION
<<memmem>>---find memory segment
INDEX
memmem
ANSI_SYNOPSIS
#include <string.h>
char *memmem(const void *<[s1]>, size_t <[l1]>, const void *<[s2]>,
size_t <[l2]>);
DESCRIPTION
Locates the first occurrence in the memory region pointed to
by <[s1]> with length <[l1]> of the sequence of bytes pointed
to by <[s2]> of length <[l2]>. If you already know the
lengths of your haystack and needle, <<memmem>> can be much
faster than <<strstr>>.
RETURNS
Returns a pointer to the located segment, or a null pointer if
<[s2]> is not found. If <[l2]> is 0, <[s1]> is returned.
PORTABILITY
<<memmem>> is a newlib extension.
<<memmem>> requires no supporting OS subroutines.
QUICKREF
memmem pure
*/
#include <string.h>
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
# define RETURN_TYPE void *
# define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
# include "str-two-way.h"
#endif
void *
_DEFUN (memmem, (haystack_start, haystack_len, needle_start, needle_len),
const void *haystack_start _AND
size_t haystack_len _AND
const void *needle_start _AND
size_t needle_len)
{
/* Abstract memory is considered to be an array of 'unsigned char' values,
not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
const unsigned char *haystack = (const unsigned char *) haystack_start;
const unsigned char *needle = (const unsigned char *) needle_start;
if (needle_len == 0)
/* The first occurrence of the empty string is deemed to occur at
the beginning of the string. */
return (void *) haystack;
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
/* Less code size, but quadratic performance in the worst case. */
while (needle_len <= haystack_len)
{
if (!memcmp (haystack, needle, needle_len))
return (void *) haystack;
haystack++;
haystack_len--;
}
return NULL;
#else /* compilation for speed */
/* Larger code size, but guaranteed linear performance. */
/* Sanity check, otherwise the loop might search through the whole
memory. */
if (haystack_len < needle_len)
return NULL;
/* Use optimizations in memchr when possible, to reduce the search
size of haystack using a linear algorithm with a smaller
coefficient. However, avoid memchr for long needles, since we
can often achieve sublinear performance. */
if (needle_len < LONG_NEEDLE_THRESHOLD)
{
haystack = memchr (haystack, *needle, haystack_len);
if (!haystack || needle_len == 1)
return (void *) haystack;
haystack_len -= haystack - (const unsigned char *) haystack_start;
if (haystack_len < needle_len)
return NULL;
return two_way_short_needle (haystack, haystack_len, needle, needle_len);
}
return two_way_long_needle (haystack, haystack_len, needle, needle_len);
#endif /* compilation for speed */
}

415
newlib/libc/string/str-two-way.h Normal file
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@ -0,0 +1,415 @@
/* Byte-wise substring search, using the Two-Way algorithm.
* Copyright (C) 2008 Eric Blake
* Permission to use, copy, modify, and distribute this software
* is freely granted, provided that this notice is preserved.
*/
/* Before including this file, you need to include <string.h>, and define:
RESULT_TYPE A macro that expands to the return type.
AVAILABLE(h, h_l, j, n_l) A macro that returns nonzero if there are
at least N_L bytes left starting at
H[J]. H is 'unsigned char *', H_L, J,
and N_L are 'size_t'; H_L is an
lvalue. For NUL-terminated searches,
H_L can be modified each iteration to
avoid having to compute the end of H
up front.
For case-insensitivity, you may optionally define:
CMP_FUNC(p1, p2, l) A macro that returns 0 iff the first L
characters of P1 and P2 are equal.
CANON_ELEMENT(c) A macro that canonicalizes an element
right after it has been fetched from
one of the two strings. The argument
is an 'unsigned char'; the result must
be an 'unsigned char' as well.
This file undefines the macros documented above, and defines
LONG_NEEDLE_THRESHOLD.
*/
#include <limits.h>
#include <stdint.h>
/* We use the Two-Way string matching algorithm, which guarantees
linear complexity with constant space. Additionally, for long
needles, we also use a bad character shift table similar to the
Boyer-Moore algorithm to achieve improved (potentially sub-linear)
performance.
See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
*/
/* Point at which computing a bad-byte shift table is likely to be
worthwhile. Small needles should not compute a table, since it
adds (1 << CHAR_BIT) + NEEDLE_LEN computations of preparation for a
speedup no greater than a factor of NEEDLE_LEN. The larger the
needle, the better the potential performance gain. On the other
hand, on non-POSIX systems with CHAR_BIT larger than eight, the
memory required for the table is prohibitive. */
#if CHAR_BIT < 10
# define LONG_NEEDLE_THRESHOLD 32U
#else
# define LONG_NEEDLE_THRESHOLD SIZE_MAX
#endif
#define MAX(a, b) ((a < b) ? (b) : (a))
#ifndef CANON_ELEMENT
# define CANON_ELEMENT(c) c
#endif
#ifndef CMP_FUNC
# define CMP_FUNC memcmp
#endif
/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
Return the index of the first byte in the right half, and set
*PERIOD to the global period of the right half.
The global period of a string is the smallest index (possibly its
length) at which all remaining bytes in the string are repetitions
of the prefix (the last repetition may be a subset of the prefix).
When NEEDLE is factored into two halves, a local period is the
length of the smallest word that shares a suffix with the left half
and shares a prefix with the right half. All factorizations of a
non-empty NEEDLE have a local period of at least 1 and no greater
than NEEDLE_LEN.
A critical factorization has the property that the local period
equals the global period. All strings have at least one critical
factorization with the left half smaller than the global period.
Given an ordered alphabet, a critical factorization can be computed
in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
larger of two ordered maximal suffixes. The ordered maximal
suffixes are determined by lexicographic comparison of
periodicity. */
static size_t
critical_factorization (const unsigned char *needle, size_t needle_len,
size_t *period)
{
/* Index of last byte of left half, or SIZE_MAX. */
size_t max_suffix, max_suffix_rev;
size_t j; /* Index into NEEDLE for current candidate suffix. */
size_t k; /* Offset into current period. */
size_t p; /* Intermediate period. */
unsigned char a, b; /* Current comparison bytes. */
/* Invariants:
0 <= j < NEEDLE_LEN - 1
-1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
min(max_suffix, max_suffix_rev) < global period of NEEDLE
1 <= p <= global period of NEEDLE
p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
1 <= k <= p
*/
/* Perform lexicographic search. */
max_suffix = SIZE_MAX;
j = 0;
k = p = 1;
while (j + k < needle_len)
{
a = CANON_ELEMENT (needle[j + k]);
b = CANON_ELEMENT (needle[max_suffix + k]);
if (a < b)
{
/* Suffix is smaller, period is entire prefix so far. */
j += k;
k = 1;
p = j - max_suffix;
}
else if (a == b)
{
/* Advance through repetition of the current period. */
if (k != p)
++k;
else
{
j += p;
k = 1;
}
}
else /* b < a */
{
/* Suffix is larger, start over from current location. */
max_suffix = j++;
k = p = 1;
}
}
*period = p;
/* Perform reverse lexicographic search. */
max_suffix_rev = SIZE_MAX;
j = 0;
k = p = 1;
while (j + k < needle_len)
{
a = CANON_ELEMENT (needle[j + k]);
b = CANON_ELEMENT (needle[max_suffix_rev + k]);
if (b < a)
{
/* Suffix is smaller, period is entire prefix so far. */
j += k;
k = 1;
p = j - max_suffix_rev;
}
else if (a == b)
{
/* Advance through repetition of the current period. */
if (k != p)
++k;
else
{
j += p;
k = 1;
}
}
else /* a < b */
{
/* Suffix is larger, start over from current location. */
max_suffix_rev = j++;
k = p = 1;
}
}
/* Choose the longer suffix. Return the first byte of the right
half, rather than the last byte of the left half. */
if (max_suffix_rev + 1 < max_suffix + 1)
return max_suffix + 1;
*period = p;
return max_suffix_rev + 1;
}
/* Return the first location of non-empty NEEDLE within HAYSTACK, or
NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This
method is optimized for NEEDLE_LEN < LONG_NEEDLE_THRESHOLD.
Performance is guaranteed to be linear, with an initialization cost
of 2 * NEEDLE_LEN comparisons.
If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.
If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. */
static RETURN_TYPE
two_way_short_needle (const unsigned char *haystack, size_t haystack_len,
const unsigned char *needle, size_t needle_len)
{
size_t i; /* Index into current byte of NEEDLE. */
size_t j; /* Index into current window of HAYSTACK. */
size_t period; /* The period of the right half of needle. */
size_t suffix; /* The index of the right half of needle. */
/* Factor the needle into two halves, such that the left half is
smaller than the global period, and the right half is
periodic (with a period as large as NEEDLE_LEN - suffix). */
suffix = critical_factorization (needle, needle_len, &period);
/* Perform the search. Each iteration compares the right half
first. */
if (CMP_FUNC (needle, needle + period, suffix) == 0)
{
/* Entire needle is periodic; a mismatch can only advance by the
period, so use memory to avoid rescanning known occurrences
of the period. */
size_t memory = 0;
j = 0;
while (AVAILABLE (haystack, haystack_len, j, needle_len))
{
/* Scan for matches in right half. */
i = MAX (suffix, memory);
while (i < needle_len && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
++i;
if (needle_len <= i)
{
/* Scan for matches in left half. */
i = suffix - 1;
while (memory < i + 1 && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
--i;
if (i + 1 < memory + 1)
return (RETURN_TYPE) (haystack + j);
/* No match, so remember how many repetitions of period
on the right half were scanned. */
j += period;
memory = needle_len - period;
}
else
{
j += i - suffix + 1;
memory = 0;
}
}
}
else
{
/* The two halves of needle are distinct; no extra memory is
required, and any mismatch results in a maximal shift. */
period = MAX (suffix, needle_len - suffix) + 1;
j = 0;
while (AVAILABLE (haystack, haystack_len, j, needle_len))
{
/* Scan for matches in right half. */
i = suffix;
while (i < needle_len && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
++i;
if (needle_len <= i)
{
/* Scan for matches in left half. */
i = suffix - 1;
while (i != SIZE_MAX && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
--i;
if (i == SIZE_MAX)
return (RETURN_TYPE) (haystack + j);
j += period;
}
else
j += i - suffix + 1;
}
}
return NULL;
}
/* Return the first location of non-empty NEEDLE within HAYSTACK, or
NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This
method is optimized for LONG_NEEDLE_THRESHOLD <= NEEDLE_LEN.
Performance is guaranteed to be linear, with an initialization cost
of 3 * NEEDLE_LEN + (1 << CHAR_BIT) operations.
If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching,
and sublinear performance O(HAYSTACK_LEN / NEEDLE_LEN) is possible.
If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, and
sublinear performance is not possible. */
static RETURN_TYPE
two_way_long_needle (const unsigned char *haystack, size_t haystack_len,
const unsigned char *needle, size_t needle_len)
{
size_t i; /* Index into current byte of NEEDLE. */
size_t j; /* Index into current window of HAYSTACK. */
size_t period; /* The period of the right half of needle. */
size_t suffix; /* The index of the right half of needle. */
size_t shift_table[1U << CHAR_BIT]; /* See below. */
/* Factor the needle into two halves, such that the left half is
smaller than the global period, and the right half is
periodic (with a period as large as NEEDLE_LEN - suffix). */
suffix = critical_factorization (needle, needle_len, &period);
/* Populate shift_table. For each possible byte value c,
shift_table[c] is the distance from the last occurrence of c to
the end of NEEDLE, or NEEDLE_LEN if c is absent from the NEEDLE.
shift_table[NEEDLE[NEEDLE_LEN - 1]] contains the only 0. */
for (i = 0; i < 1U << CHAR_BIT; i++)
shift_table[i] = needle_len;
for (i = 0; i < needle_len; i++)
shift_table[CANON_ELEMENT (needle[i])] = needle_len - i - 1;
/* Perform the search. Each iteration compares the right half
first. */
if (CMP_FUNC (needle, needle + period, suffix) == 0)
{
/* Entire needle is periodic; a mismatch can only advance by the
period, so use memory to avoid rescanning known occurrences
of the period. */
size_t memory = 0;
size_t shift;
j = 0;
while (AVAILABLE (haystack, haystack_len, j, needle_len))
{
/* Check the last byte first; if it does not match, then
shift to the next possible match location. */
shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])];
if (0 < shift)
{
if (memory && shift < period)
{
/* Since needle is periodic, but the last period has
a byte out of place, there can be no match until
after the mismatch. */
shift = needle_len - period;
memory = 0;
}
j += shift;
continue;
}
/* Scan for matches in right half. The last byte has
already been matched, by virtue of the shift table. */
i = MAX (suffix, memory);
while (i < needle_len - 1 && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
++i;
if (needle_len - 1 <= i)
{
/* Scan for matches in left half. */
i = suffix - 1;
while (memory < i + 1 && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
--i;
if (i + 1 < memory + 1)
return (RETURN_TYPE) (haystack + j);
/* No match, so remember how many repetitions of period
on the right half were scanned. */
j += period;
memory = needle_len - period;
}
else
{
j += i - suffix + 1;
memory = 0;
}
}
}
else
{
/* The two halves of needle are distinct; no extra memory is
required, and any mismatch results in a maximal shift. */
size_t shift;
period = MAX (suffix, needle_len - suffix) + 1;
j = 0;
while (AVAILABLE (haystack, haystack_len, j, needle_len))
{
/* Check the last byte first; if it does not match, then
shift to the next possible match location. */
shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])];
if (0 < shift)
{
j += shift;
continue;
}
/* Scan for matches in right half. The last byte has
already been matched, by virtue of the shift table. */
i = suffix;
while (i < needle_len - 1 && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
++i;
if (needle_len - 1 <= i)
{
/* Scan for matches in left half. */
i = suffix - 1;
while (i != SIZE_MAX && (CANON_ELEMENT (needle[i])
== CANON_ELEMENT (haystack[i + j])))
--i;
if (i == SIZE_MAX)
return (RETURN_TYPE) (haystack + j);
j += period;
}
else
j += i - suffix + 1;
}
}
return NULL;
}
#undef AVAILABLE
#undef CANON_ELEMENT
#undef CMP_FUNC
#undef MAX
#undef RETURN_TYPE

51
newlib/libc/string/strcasestr.c
View File

@ -40,7 +40,7 @@ QUICKREF
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* The quadratic code is derived from software contributed to Berkeley by
* Chris Torek.
*
* Redistribution and use in source and binary forms, with or without
@ -67,12 +67,26 @@ QUICKREF
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/* Linear algorithm Copyright (C) 2008 Eric Blake
* Permission to use, copy, modify, and distribute the linear portion of
* software is freely granted, provided that this notice is preserved.
*/
#include <sys/cdefs.h>
#include <ctype.h>
#include <string.h>
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
# define RETURN_TYPE char *
# define AVAILABLE(h, h_l, j, n_l) \
(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
&& ((h_l) = (j) + (n_l)))
# define CANON_ELEMENT(c) tolower (c)
# define CMP_FUNC strncasecmp
# include "str-two-way.h"
#endif
/*
* Find the first occurrence of find in s, ignore case.
*/
@ -80,6 +94,9 @@ char *
strcasestr(s, find)
const char *s, *find;
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
/* Less code size, but quadratic performance in the worst case. */
char c, sc;
size_t len;
@ -95,4 +112,36 @@ strcasestr(s, find)
s--;
}
return ((char *)s);
#else /* compilation for speed */
/* Larger code size, but guaranteed linear performance. */
const char *haystack = s;
const char *needle = find;
size_t needle_len; /* Length of NEEDLE. */
size_t haystack_len; /* Known minimum length of HAYSTACK. */
int ok = 1; /* True if NEEDLE is prefix of HAYSTACK. */
/* Determine length of NEEDLE, and in the process, make sure
HAYSTACK is at least as long (no point processing all of a long
NEEDLE if HAYSTACK is too short). */
while (*haystack && *needle)
ok &= (tolower ((unsigned char) *haystack++)
== tolower ((unsigned char) *needle++));
if (*needle)
return NULL;
if (ok)
return (char *) s;
needle_len = needle - find;
haystack = s + 1;
haystack_len = needle_len - 1;
/* Perform the search. */
if (needle_len < LONG_NEEDLE_THRESHOLD)
return two_way_short_needle ((const unsigned char *) haystack,
haystack_len,
(const unsigned char *) find, needle_len);
return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
(const unsigned char *) find, needle_len);
#endif /* compilation for speed */
}

4
newlib/libc/string/strings.tex
View File

@ -14,6 +14,7 @@ managing areas of memory. The corresponding declarations are in
* memchr:: Find character in memory
* memcmp:: Compare two memory areas
* memcpy:: Copy memory regions
* memmem:: Find memory segment
* memmove:: Move possibly overlapping memory
* mempcpy:: Copy memory regions and locate end
* memset:: Set an area of memory
@ -71,6 +72,9 @@ managing areas of memory. The corresponding declarations are in
@page
@include string/memcpy.def
@page
@include string/memmem.def
@page
@include string/memmove.def

52
newlib/libc/string/strstr.c
View File

@ -16,14 +16,14 @@ TRAD_SYNOPSIS
char *<[s2]>;
DESCRIPTION
Locates the first occurence in the string pointed to by <[s1]> of
Locates the first occurrence in the string pointed to by <[s1]> of
the sequence of characters in the string pointed to by <[s2]>
(excluding the terminating null character).
RETURNS
Returns a pointer to the located string segment, or a null
pointer if the string <[s2]> is not found. If <[s2]> points to
a string with zero length, the <[s1]> is returned.
a string with zero length, <[s1]> is returned.
PORTABILITY
<<strstr>> is ANSI C.
@ -36,11 +36,22 @@ QUICKREF
#include <string.h>
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
# define RETURN_TYPE char *
# define AVAILABLE(h, h_l, j, n_l) \
(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
&& ((h_l) = (j) + (n_l)))
# include "str-two-way.h"
#endif
char *
_DEFUN (strstr, (searchee, lookfor),
_CONST char *searchee _AND
_CONST char *lookfor)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
/* Less code size, but quadratic performance in the worst case. */
if (*searchee == 0)
{
if (*lookfor)
@ -70,4 +81,41 @@ _DEFUN (strstr, (searchee, lookfor),
}
return (char *) NULL;
#else /* compilation for speed */
/* Larger code size, but guaranteed linear performance. */
const char *haystack = searchee;
const char *needle = lookfor;
size_t needle_len; /* Length of NEEDLE. */
size_t haystack_len; /* Known minimum length of HAYSTACK. */
int ok = 1; /* True if NEEDLE is prefix of HAYSTACK. */
/* Determine length of NEEDLE, and in the process, make sure
HAYSTACK is at least as long (no point processing all of a long
NEEDLE if HAYSTACK is too short). */
while (*haystack && *needle)
ok &= *haystack++ == *needle++;
if (*needle)
return NULL;
if (ok)
return (char *) searchee;
/* Reduce the size of haystack using strchr, since it has a smaller
linear coefficient than the Two-Way algorithm. */
needle_len = needle - lookfor;
haystack = strchr (searchee + 1, *lookfor);
if (!haystack || needle_len == 1)
return (char *) haystack;
haystack_len = (haystack > searchee + needle_len ? 1
: needle_len + searchee - haystack);
/* Perform the search. */
if (needle_len < LONG_NEEDLE_THRESHOLD)
return two_way_short_needle ((const unsigned char *) haystack,
haystack_len,
(const unsigned char *) lookfor, needle_len);
return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
(const unsigned char *) lookfor, needle_len);
#endif /* compilation for speed */
}