@@ -21,177 +21,64 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <stdlib.h>
-
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
-#if defined _LIBC
-# include <string.h>
-# include <memcopy.h>
-#endif
-
-#if defined HAVE_LIMITS_H || defined _LIBC
-# include <limits.h>
-#endif
-
-#define LONG_MAX_32_BITS 2147483647
-
-#ifndef LONG_MAX
-# define LONG_MAX LONG_MAX_32_BITS
-#endif
-
-#include <sys/types.h>
+#include <string.h>
+#include <stdint.h>
+#include <limits.h>
+#include <string-fzb.h>
+#include <string-fzi.h>
+#include <string-opthr.h>
+#include <string-maskoff.h>
#undef __memrchr
#undef memrchr
-#ifndef weak_alias
-# define __memrchr memrchr
+#ifndef MEMRCHR
+# define MEMRCHR __memrchr
#endif
-/* Search no more than N bytes of S for C. */
void *
-#ifndef MEMRCHR
-__memrchr
-#else
-MEMRCHR
-#endif
- (const void *s, int c_in, size_t n)
+MEMRCHR (const void *s, int c_in, size_t n)
{
- const unsigned char *char_ptr;
- const unsigned long int *longword_ptr;
- unsigned long int longword, magic_bits, charmask;
- unsigned char c;
-
- c = (unsigned char) c_in;
+ uintptr_t s_int = (uintptr_t) s;
+ uintptr_t lbyte_int = s_int + n;
/* Handle the last few characters by reading one character at a time.
- Do this until CHAR_PTR is aligned on a longword boundary. */
- for (char_ptr = (const unsigned char *) s + n;
- n > 0 && ((unsigned long int) char_ptr
- & (sizeof (longword) - 1)) != 0;
- --n)
- if (*--char_ptr == c)
+ Do this until CHAR_PTR is aligned on a word boundary, or
+ the entirety of small inputs. */
+ const unsigned char *char_ptr = (const unsigned char *) lbyte_int;
+ size_t align = lbyte_int % sizeof (op_t);
+ if (n < OP_T_THRES || align > n)
+ align = n;
+ for (size_t i = 0; i < align; ++i)
+ if (*--char_ptr == c_in)
return (void *) char_ptr;
- /* All these elucidatory comments refer to 4-byte longwords,
- but the theory applies equally well to 8-byte longwords. */
-
- longword_ptr = (const unsigned long int *) char_ptr;
-
- /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
- the "holes." Note that there is a hole just to the left of
- each byte, with an extra at the end:
-
- bits: 01111110 11111110 11111110 11111111
- bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
-
- The 1-bits make sure that carries propagate to the next 0-bit.
- The 0-bits provide holes for carries to fall into. */
- magic_bits = -1;
- magic_bits = magic_bits / 0xff * 0xfe << 1 >> 1 | 1;
+ const op_t *word_ptr = (const op_t *) char_ptr;
+ n -= align;
+ if (__glibc_unlikely (n == 0))
+ return NULL;
- /* Set up a longword, each of whose bytes is C. */
- charmask = c | (c << 8);
- charmask |= charmask << 16;
-#if LONG_MAX > LONG_MAX_32_BITS
- charmask |= charmask << 32;
-#endif
-
- /* Instead of the traditional loop which tests each character,
- we will test a longword at a time. The tricky part is testing
- if *any of the four* bytes in the longword in question are zero. */
- while (n >= sizeof (longword))
- {
- /* We tentatively exit the loop if adding MAGIC_BITS to
- LONGWORD fails to change any of the hole bits of LONGWORD.
-
- 1) Is this safe? Will it catch all the zero bytes?
- Suppose there is a byte with all zeros. Any carry bits
- propagating from its left will fall into the hole at its
- least significant bit and stop. Since there will be no
- carry from its most significant bit, the LSB of the
- byte to the left will be unchanged, and the zero will be
- detected.
-
- 2) Is this worthwhile? Will it ignore everything except
- zero bytes? Suppose every byte of LONGWORD has a bit set
- somewhere. There will be a carry into bit 8. If bit 8
- is set, this will carry into bit 16. If bit 8 is clear,
- one of bits 9-15 must be set, so there will be a carry
- into bit 16. Similarly, there will be a carry into bit
- 24. If one of bits 24-30 is set, there will be a carry
- into bit 31, so all of the hole bits will be changed.
-
- The one misfire occurs when bits 24-30 are clear and bit
- 31 is set; in this case, the hole at bit 31 is not
- changed. If we had access to the processor carry flag,
- we could close this loophole by putting the fourth hole
- at bit 32!
-
- So it ignores everything except 128's, when they're aligned
- properly.
-
- 3) But wait! Aren't we looking for C, not zero?
- Good point. So what we do is XOR LONGWORD with a longword,
- each of whose bytes is C. This turns each byte that is C
- into a zero. */
-
- longword = *--longword_ptr ^ charmask;
+ /* Compute the address of the word containing the initial byte. */
+ const op_t *lword = (const op_t *) (s_int & -sizeof (op_t));
- /* Add MAGIC_BITS to LONGWORD. */
- if ((((longword + magic_bits)
+ /* Set up a word, each of whose bytes is C. */
+ op_t repeated_c = repeat_bytes (c_in);
- /* Set those bits that were unchanged by the addition. */
- ^ ~longword)
+ char *ret;
+ op_t word;
- /* Look at only the hole bits. If any of the hole bits
- are unchanged, most likely one of the bytes was a
- zero. */
- & ~magic_bits) != 0)
- {
- /* Which of the bytes was C? If none of them were, it was
- a misfire; continue the search. */
-
- const unsigned char *cp = (const unsigned char *) longword_ptr;
-
-#if LONG_MAX > 2147483647
- if (cp[7] == c)
- return (void *) &cp[7];
- if (cp[6] == c)
- return (void *) &cp[6];
- if (cp[5] == c)
- return (void *) &cp[5];
- if (cp[4] == c)
- return (void *) &cp[4];
-#endif
- if (cp[3] == c)
- return (void *) &cp[3];
- if (cp[2] == c)
- return (void *) &cp[2];
- if (cp[1] == c)
- return (void *) &cp[1];
- if (cp[0] == c)
- return (void *) cp;
- }
-
- n -= sizeof (longword);
- }
-
- char_ptr = (const unsigned char *) longword_ptr;
-
- while (n-- > 0)
+ while (word_ptr != lword)
{
- if (*--char_ptr == c)
- return (void *) char_ptr;
+ word = *--word_ptr;
+ if (has_eq (word, repeated_c))
+ goto found;
}
+ return NULL;
- return 0;
+found:
+ /* We found a match, but it might be in a byte past the start
+ of the array. */
+ ret = (char *) word_ptr + index_last_eq (word, repeated_c);
+ return (ret >= (char*) s) ? ret : NULL;
}
-#ifndef MEMRCHR
-# ifdef weak_alias
weak_alias (__memrchr, memrchr)
-# endif
-#endif
@@ -1,5 +1,7 @@
#if IS_IN (libc)
# define MEMRCHR __memrchr_ia32
+# undef weak_alias
+# define weak_alias(a,b)
# include <string.h>
extern void *__memrchr_ia32 (const void *, int, size_t);
#endif
@@ -18,6 +18,8 @@
#if defined HAVE_S390_VX_ASM_SUPPORT && IS_IN (libc)
# define MEMRCHR __memrchr_c
+# undef weak_alias
+# define weak_alias(a,b)
# include <string.h>
extern __typeof (__memrchr) __memrchr_c;
From: Richard Henderson <rth@twiddle.net> New algorithm have the following key differences: - Use string-fz{b,i} functions. It also cleanups the multiple inclusion by leaving the ifunc implementation to undef the weak_alias. Checked on x86_64-linux-gnu, i686-linux-gnu, sparc64-linux-gnu, and sparcv9-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Richard Henderson <rth@twiddle.net> Adhemerval Zanella <adhemerval.zanella@linaro.org> [BZ #5806] * string/memrchr.c: Use string-fzb.h, string-fzi.h. * sysdeps/i386/i686/multiarch/memrchr-c.c: Redefined weak_alias. * sysdeps/s390/multiarch/memrchr-c.c: Likewise. --- string/memrchr.c | 193 +++++++------------------------- sysdeps/i386/i686/multiarch/memrchr-c.c | 2 + sysdeps/s390/multiarch/memrchr-c.c | 2 + 3 files changed, 44 insertions(+), 153 deletions(-) -- 2.7.4