@@ -1,10 +1,6 @@
-/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
+/* Scan memory for a character. Generic version
+ Copyright (C) 1991-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
- Based on strlen implementation by Torbjorn Granlund (tege@sics.se),
- with help from Dan Sahlin (dan@sics.se) and
- commentary by Jim Blandy (jimb@ai.mit.edu);
- adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu),
- and implemented by Roland McGrath (roland@ai.mit.edu).
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
@@ -20,143 +16,76 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
-#ifndef _LIBC
-# include <config.h>
-#endif
-
+#include <intprops.h>
+#include <string-fza.h>
+#include <string-fzb.h>
+#include <string-fzi.h>
+#include <string-maskoff.h>
+#include <string-opthr.h>
#include <string.h>
-#include <stddef.h>
-
-#include <limits.h>
+#undef memchr
-#undef __memchr
-#ifdef _LIBC
-# undef memchr
+#ifdef MEMCHR
+# define __memchr MEMCHR
#endif
-#ifndef weak_alias
-# define __memchr memchr
-#endif
-
-#ifndef MEMCHR
-# define MEMCHR __memchr
-#endif
+static inline const char *
+sadd (uintptr_t x, uintptr_t y)
+{
+ uintptr_t ret = INT_ADD_OVERFLOW (x, y) ? (uintptr_t)-1 : x + y;
+ return (const char *)ret;
+}
/* Search no more than N bytes of S for C. */
void *
-MEMCHR (void const *s, int c_in, size_t n)
+__memchr (void const *s, int c_in, size_t n)
{
- /* On 32-bit hardware, choosing longword to be a 32-bit unsigned
- long instead of a 64-bit uintmax_t tends to give better
- performance. On 64-bit hardware, unsigned long is generally 64
- bits already. Change this typedef to experiment with
- performance. */
- typedef unsigned long int longword;
-
- const unsigned char *char_ptr;
- const longword *longword_ptr;
- longword repeated_one;
- longword repeated_c;
- unsigned char c;
-
- c = (unsigned char) c_in;
+ if (__glibc_unlikely (n == 0))
+ return NULL;
- /* Handle the first few bytes by reading one byte at a time.
- Do this until CHAR_PTR is aligned on a longword boundary. */
- for (char_ptr = (const unsigned char *) s;
- n > 0 && (size_t) char_ptr % sizeof (longword) != 0;
- --n, ++char_ptr)
- if (*char_ptr == c)
- return (void *) char_ptr;
+ /* Read the first word, but munge it so that bytes before the array
+ will not match goal. */
+ const op_t *word_ptr = word_containing (s);
+ uintptr_t s_int = (uintptr_t) s;
- longword_ptr = (const longword *) char_ptr;
+ op_t word = *word_ptr;
+ op_t repeated_c = repeat_bytes (c_in);
+ op_t mask = check_mask (find_eq_all (word, repeated_c), s_int);
- /* All these elucidatory comments refer to 4-byte longwords,
- but the theory applies equally well to any size longwords. */
+ /* Compute the address of the last byte taking in consideration possible
+ overflow. */
+ const char *lbyte = sadd (s_int, n - 1);
+ /* And also the address of the word containing the last byte. */
+ const op_t *lword = word_containing (lbyte);
- /* Compute auxiliary longword values:
- repeated_one is a value which has a 1 in every byte.
- repeated_c has c in every byte. */
- repeated_one = 0x01010101;
- repeated_c = c | (c << 8);
- repeated_c |= repeated_c << 16;
- if (0xffffffffU < (longword) -1)
+ if (mask != 0)
{
- repeated_one |= repeated_one << 31 << 1;
- repeated_c |= repeated_c << 31 << 1;
- if (8 < sizeof (longword))
- {
- size_t i;
-
- for (i = 64; i < sizeof (longword) * 8; i *= 2)
- {
- repeated_one |= repeated_one << i;
- repeated_c |= repeated_c << i;
- }
- }
+ char *ret = (char *) s + index_first (mask);
+ return (ret <= lbyte) ? ret : NULL;
}
+ if (word_ptr == lword)
+ return NULL;
- /* Instead of the traditional loop which tests each byte, 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 equal to c. We first use an xor
- with repeated_c. This reduces the task to testing whether *any of the
- four* bytes in longword1 is zero.
-
- We compute tmp =
- ((longword1 - repeated_one) & ~longword1) & (repeated_one << 7).
- That is, we perform the following operations:
- 1. Subtract repeated_one.
- 2. & ~longword1.
- 3. & a mask consisting of 0x80 in every byte.
- Consider what happens in each byte:
- - If a byte of longword1 is zero, step 1 and 2 transform it into 0xff,
- and step 3 transforms it into 0x80. A carry can also be propagated
- to more significant bytes.
- - If a byte of longword1 is nonzero, let its lowest 1 bit be at
- position k (0 <= k <= 7); so the lowest k bits are 0. After step 1,
- the byte ends in a single bit of value 0 and k bits of value 1.
- After step 2, the result is just k bits of value 1: 2^k - 1. After
- step 3, the result is 0. And no carry is produced.
- So, if longword1 has only non-zero bytes, tmp is zero.
- Whereas if longword1 has a zero byte, call j the position of the least
- significant zero byte. Then the result has a zero at positions 0, ...,
- j-1 and a 0x80 at position j. We cannot predict the result at the more
- significant bytes (positions j+1..3), but it does not matter since we
- already have a non-zero bit at position 8*j+7.
-
- So, the test whether any byte in longword1 is zero is equivalent to
- testing whether tmp is nonzero. */
-
- while (n >= sizeof (longword))
+ word = *++word_ptr;
+ while (word_ptr != lword)
{
- longword longword1 = *longword_ptr ^ repeated_c;
-
- if ((((longword1 - repeated_one) & ~longword1)
- & (repeated_one << 7)) != 0)
- break;
- longword_ptr++;
- n -= sizeof (longword);
+ if (has_eq (word, repeated_c))
+ return (char *) word_ptr + index_first_eq (word, repeated_c);
+ word = *++word_ptr;
}
- char_ptr = (const unsigned char *) longword_ptr;
-
- /* At this point, we know that either n < sizeof (longword), or one of the
- sizeof (longword) bytes starting at char_ptr is == c. On little-endian
- machines, we could determine the first such byte without any further
- memory accesses, just by looking at the tmp result from the last loop
- iteration. But this does not work on big-endian machines. Choose code
- that works in both cases. */
-
- for (; n > 0; --n, ++char_ptr)
+ if (has_eq (word, repeated_c))
{
- if (*char_ptr == c)
- return (void *) char_ptr;
+ /* We found a match, but it might be in a byte past the end of the
+ array. */
+ char *ret = (char *) word_ptr + index_first_eq (word, repeated_c);
+ if (ret <= lbyte)
+ return ret;
}
-
return NULL;
}
-#ifdef weak_alias
+#ifndef MEMCHR
weak_alias (__memchr, memchr)
-#endif
libc_hidden_builtin_def (memchr)
+#endif
@@ -18,17 +18,11 @@
#include <string.h>
-#define MEMCHR __memchr_ppc
+extern __typeof (memchr) __memchr_ppc attribute_hidden;
-#undef weak_alias
-#define weak_alias(a, b)
+#define MEMCHR __memchr_ppc
+#include <string/memchr.c>
#ifdef SHARED
-# undef libc_hidden_builtin_def
-# define libc_hidden_builtin_def(name) \
- __hidden_ver1(__memchr_ppc, __GI_memchr, __memchr_ppc);
+__hidden_ver1(__memchr_ppc, __GI_memchr, __memchr_ppc);
#endif
-
-extern __typeof (memchr) __memchr_ppc attribute_hidden;
-
-#include <string/memchr.c>
@@ -18,14 +18,7 @@
#include <string.h>
-#define MEMCHR __memchr_ppc
-
-#undef weak_alias
-#define weak_alias(a, b)
-
-# undef libc_hidden_builtin_def
-# define libc_hidden_builtin_def(name)
-
extern __typeof (memchr) __memchr_ppc attribute_hidden;
+#define MEMCHR __memchr_ppc
#include <string/memchr.c>
From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> New algorithm have the following key differences: - Reads first word unaligned and use string-maskoff function to remove unwanted data. This strategy follow arch-specific optimization used on aarch64 and powerpc. - Use string-fz{b,i} and string-opthr functions. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu, and powerpc64-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Co-authored-by: Richard Henderson <richard.henderson@linaro.org> --- string/memchr.c | 171 +++++------------- .../powerpc32/power4/multiarch/memchr-ppc32.c | 14 +- .../powerpc64/multiarch/memchr-ppc64.c | 9 +- 3 files changed, 55 insertions(+), 139 deletions(-)