@@ -21,180 +21,85 @@
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
-
-#undef __ptr_t
-#define __ptr_t void *
-
-#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>
#undef __memrchr
#undef memrchr
-#ifndef weak_alias
-# define __memrchr memrchr
-#endif
-
/* Search no more than N bytes of S for C. */
-__ptr_t
-#ifndef MEMRCHR
-__memrchr
-#else
-MEMRCHR
+
+#ifdef MEMRCHR
+# define __memrchr MEMRCHR
#endif
- (const __ptr_t s, int c_in, size_t n)
+
+void *
+__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;
+ const unsigned char *char_ptr = (const unsigned char *) s + n;
+ const op_t *word_ptr;
+ op_t word, repeated_c;
+ uintptr_t i, align;
unsigned char c;
c = (unsigned char) c_in;
/* 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)
+ Do this until CHAR_PTR is aligned on a word boundary, or
+ the entirety of small inputs. */
+ align = (uintptr_t)char_ptr % sizeof (word);
+ if (n < OP_T_THRES || align > n)
+ align = n;
+ for (i = 0; i < align; ++i)
if (*--char_ptr == c)
- return (__ptr_t) 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:
+ return (void *) char_ptr;
- bits: 01111110 11111110 11111110 11111111
- bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
+ /* Set up a word, each of whose bytes is C. */
+ repeated_c = ((op_t)-1 / 0xff) * c;
- 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;
+ 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))
+ /* Loop while we have at least one word remaining. */
+ while (n >= sizeof (word))
{
- /* 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;
-
- /* Add MAGIC_BITS to LONGWORD. */
- if ((((longword + magic_bits)
-
- /* Set those bits that were unchanged by the addition. */
- ^ ~longword)
-
- /* 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)
+ word = *--word_ptr;
+ if (has_eq (word, repeated_c))
{
- /* 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 (__ptr_t) &cp[7];
- if (cp[6] == c)
- return (__ptr_t) &cp[6];
- if (cp[5] == c)
- return (__ptr_t) &cp[5];
- if (cp[4] == c)
- return (__ptr_t) &cp[4];
-#endif
- if (cp[3] == c)
- return (__ptr_t) &cp[3];
- if (cp[2] == c)
- return (__ptr_t) &cp[2];
- if (cp[1] == c)
- return (__ptr_t) &cp[1];
- if (cp[0] == c)
- return (__ptr_t) cp;
+ word ^= repeated_c;
+ goto found;
}
-
- n -= sizeof (longword);
+ n -= sizeof (word);
}
- char_ptr = (const unsigned char *) longword_ptr;
-
- while (n-- > 0)
+ /* Handle any remaining portion of a word. */
+ if (n > 0)
{
- if (*--char_ptr == c)
- return (__ptr_t) char_ptr;
- }
+ word = *--word_ptr ^ repeated_c;
- return 0;
+ /* Mask out the garbage bytes at the front of WORD. */
+ op_t m = -1;
+ if (__BYTE_ORDER == __LITTLE_ENDIAN)
+ m >>= n * CHAR_BIT;
+ else
+ m <<= n * CHAR_BIT;
+ word |= m;
+
+ if (has_zero (word))
+ {
+ found:
+ return (char *) word_ptr + index_last_zero (word);
+ }
+ }
+ return NULL;
}
+
#ifndef MEMRCHR
-# ifdef weak_alias
weak_alias (__memrchr, memrchr)
-# endif
#endif