diff options
-rw-r--r-- | lib/memrchr.c | 67 |
1 files changed, 41 insertions, 26 deletions
diff --git a/lib/memrchr.c b/lib/memrchr.c index 7d702f35e..d3618cb29 100644 --- a/lib/memrchr.c +++ b/lib/memrchr.c @@ -27,10 +27,11 @@ # include <config.h> #endif -#include <stdlib.h> #include <string.h> -#if defined (_LIBC) +#include <stddef.h> + +#if defined _LIBC # include <memcopy.h> #else # define reg_char char @@ -38,9 +39,19 @@ #include <limits.h> -#define LONG_MAX_32_BITS 2147483647 +#if HAVE_INTTYPES_H +# include <inttypes.h> +#endif +#if defined _LIBC || HAVE_STDINT_H +# include <stdint.h> +#endif -#include <sys/types.h> +#define alignof(type) offsetof (struct { char c; type x; }, x) +#ifdef UINTPTR_MAX +# define UNALIGNED_P(p) (((uintptr_t) p) % alignof (unsigned long int) != 0) +#else +# define UNALIGNED_P(p) 1 +#endif #undef __memrchr #undef memrchr @@ -57,22 +68,22 @@ __memrchr (void const *s, int c_in, size_t n) const unsigned long int *longword_ptr; unsigned long int longword, magic_bits, charmask; unsigned reg_char c; + int i; 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 > 0 && UNALIGNED_P (char_ptr); --n) if (*--char_ptr == c) return (void *) char_ptr; /* All these elucidatory comments refer to 4-byte longwords, - but the theory applies equally well to 8-byte longwords. */ + but the theory applies equally well to any size longwords. */ - longword_ptr = (unsigned long int *) char_ptr; + 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 @@ -84,26 +95,28 @@ __memrchr (void const *s, int c_in, size_t n) The 1-bits make sure that carries propagate to the next 0-bit. The 0-bits provide holes for carries to fall into. */ - if (sizeof (longword) != 4 && sizeof (longword) != 8) - abort (); + /* Set MAGIC_BITS to be this pattern of 1 and 0 bits. + Set CHARMASK to be a longword, each of whose bytes is C. */ -#if LONG_MAX <= LONG_MAX_32_BITS - magic_bits = 0x7efefeff; -#else - magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff; -#endif - - /* Set up a longword, each of whose bytes is C. */ + magic_bits = 0xfefefefe; charmask = c | (c << 8); charmask |= charmask << 16; -#if LONG_MAX > LONG_MAX_32_BITS +#if 0xffffffffU < ULONG_MAX + magic_bits |= magic_bits << 32; charmask |= charmask << 32; + if (8 < sizeof longword) + for (i = 64; i < sizeof longword * 8; i *= 2) + { + magic_bits |= magic_bits << i; + charmask |= charmask << i; + } #endif + magic_bits = (ULONG_MAX >> 1) & (magic_bits | 1); /* 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)) + 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. @@ -157,16 +170,18 @@ __memrchr (void const *s, int c_in, size_t n) const unsigned char *cp = (const unsigned char *) longword_ptr; -#if LONG_MAX > 2147483647 - if (cp[7] == c) + if (8 < sizeof longword) + for (i = sizeof longword - 1; 8 <= i; i--) + if (cp[i] == c) + return (void *) &cp[i]; + if (7 < sizeof longword && cp[7] == c) return (void *) &cp[7]; - if (cp[6] == c) + if (6 < sizeof longword && cp[6] == c) return (void *) &cp[6]; - if (cp[5] == c) + if (5 < sizeof longword && cp[5] == c) return (void *) &cp[5]; - if (cp[4] == c) + if (4 < sizeof longword && cp[4] == c) return (void *) &cp[4]; -#endif if (cp[3] == c) return (void *) &cp[3]; if (cp[2] == c) @@ -177,7 +192,7 @@ __memrchr (void const *s, int c_in, size_t n) return (void *) cp; } - n -= sizeof (longword); + n -= sizeof longword; } char_ptr = (const unsigned char *) longword_ptr; |