From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org
Cc: Joseph Myers <joseph@codesourcery.com>,
caiyinyu <caiyinyu@loongson.cn>,
Richard Henderson <rth@twiddle.net>
Subject: [PATCH 08/17] string: Improve generic strchrnul
Date: Fri, 2 Sep 2022 17:39:31 -0300 [thread overview]
Message-ID: <20220902203940.2385967-9-adhemerval.zanella@linaro.org> (raw)
In-Reply-To: <20220902203940.2385967-1-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} functions.
Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64-linux-gnu,
and powerpc-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 <rth@twiddle.net>
---
string/strchrnul.c | 156 +++---------------
.../power4/multiarch/strchrnul-ppc32.c | 4 -
sysdeps/s390/strchrnul-c.c | 2 -
3 files changed, 24 insertions(+), 138 deletions(-)
diff --git a/string/strchrnul.c b/string/strchrnul.c
index 0cc1fc6bb0..67defa3dab 100644
--- a/string/strchrnul.c
+++ b/string/strchrnul.c
@@ -1,10 +1,5 @@
/* Copyright (C) 1991-2022 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
- bug fix and commentary by Jim Blandy (jimb@ai.mit.edu);
- adaptation to strchr 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
@@ -21,146 +16,43 @@
<https://www.gnu.org/licenses/>. */
#include <string.h>
-#include <memcopy.h>
#include <stdlib.h>
+#include <stdint.h>
+#include <string-fza.h>
+#include <string-fzb.h>
+#include <string-fzi.h>
+#include <string-maskoff.h>
#undef __strchrnul
#undef strchrnul
-#ifndef STRCHRNUL
-# define STRCHRNUL __strchrnul
+#ifdef STRCHRNUL
+# define __strchrnul STRCHRNUL
#endif
/* Find the first occurrence of C in S or the final NUL byte. */
char *
-STRCHRNUL (const char *s, int c_in)
+__strchrnul (const char *str, int c_in)
{
- 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;
-
- /* Handle the first 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;
- ((unsigned long int) char_ptr & (sizeof (longword) - 1)) != 0;
- ++char_ptr)
- if (*char_ptr == c || *char_ptr == '\0')
- 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 = (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;
-
- /* Set up a longword, each of whose bytes is C. */
- charmask = c | (c << 8);
- charmask |= charmask << 16;
- if (sizeof (longword) > 4)
- /* Do the shift in two steps to avoid a warning if long has 32 bits. */
- charmask |= (charmask << 16) << 16;
- if (sizeof (longword) > 8)
- abort ();
-
- /* 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. */
- for (;;)
- {
- /* 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.
+ /* Set up a word, each of whose bytes is C. */
+ op_t repeated_c = repeat_bytes (c_in);
- 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.
+ /* Align the input address to op_t. */
+ uintptr_t s_int = (uintptr_t) str;
+ const op_t *word_ptr = word_containing (str);
- 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!
+ /* Read the first aligned word, but force bytes before the string to
+ match neither zero nor goal (we make sure the high bit of each byte
+ is 1, and the low 7 bits are all the opposite of the goal byte). */
+ op_t bmask = create_mask (s_int);
+ op_t word = (*word_ptr | bmask) ^ (repeated_c & highbit_mask (bmask));
- So it ignores everything except 128's, when they're aligned
- properly.
+ while (! has_zero_eq (word, repeated_c))
+ word = *++word_ptr;
- 3) But wait! Aren't we looking for C as well as 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++;
-
- /* 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
-
- /* That caught zeroes. Now test for C. */
- || ((((longword ^ charmask) + magic_bits) ^ ~(longword ^ charmask))
- & ~magic_bits) != 0)
- {
- /* Which of the bytes was C or zero?
- If none of them were, it was a misfire; continue the search. */
-
- const unsigned char *cp = (const unsigned char *) (longword_ptr - 1);
-
- if (*cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (sizeof (longword) > 4)
- {
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- if (*++cp == c || *cp == '\0')
- return (char *) cp;
- }
- }
- }
-
- /* This should never happen. */
- return NULL;
+ op_t found = index_first_zero_eq (word, repeated_c);
+ return (char *) (word_ptr) + found;
}
-
+#ifndef STRCHRNUL
weak_alias (__strchrnul, strchrnul)
+#endif
diff --git a/sysdeps/powerpc/powerpc32/power4/multiarch/strchrnul-ppc32.c b/sysdeps/powerpc/powerpc32/power4/multiarch/strchrnul-ppc32.c
index ed86b5e671..9c85e269f7 100644
--- a/sysdeps/powerpc/powerpc32/power4/multiarch/strchrnul-ppc32.c
+++ b/sysdeps/powerpc/powerpc32/power4/multiarch/strchrnul-ppc32.c
@@ -19,10 +19,6 @@
#include <string.h>
#define STRCHRNUL __strchrnul_ppc
-
-#undef weak_alias
-#define weak_alias(a,b )
-
extern __typeof (strchrnul) __strchrnul_ppc attribute_hidden;
#include <string/strchrnul.c>
diff --git a/sysdeps/s390/strchrnul-c.c b/sysdeps/s390/strchrnul-c.c
index 4ffac54edd..2ebbcc62f7 100644
--- a/sysdeps/s390/strchrnul-c.c
+++ b/sysdeps/s390/strchrnul-c.c
@@ -22,8 +22,6 @@
# if HAVE_STRCHRNUL_IFUNC
# define STRCHRNUL STRCHRNUL_C
# define __strchrnul STRCHRNUL
-# undef weak_alias
-# define weak_alias(name, alias)
# endif
# include <string/strchrnul.c>
--
2.34.1
next prev parent reply other threads:[~2022-09-02 20:39 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-02 20:39 [PATCH 00/17] Improve generic string routines Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 01/17] Parameterize op_t from memcopy.h Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 02/17] Parameterize OP_T_THRES " Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 03/17] Add string-maskoff.h generic header Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 04/17] Add string vectorized find and detection functions Adhemerval Zanella
2022-09-03 3:20 ` Noah Goldstein
2022-09-19 14:00 ` Adhemerval Zanella Netto
2022-09-02 20:39 ` [PATCH 05/17] string: Improve generic strlen Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 06/17] string: Improve generic strnlen Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 07/17] string: Improve generic strchr Adhemerval Zanella
2022-09-02 20:39 ` Adhemerval Zanella [this message]
2022-09-02 20:39 ` [PATCH 09/17] string: Improve generic strcmp Adhemerval Zanella
2022-09-03 3:31 ` Noah Goldstein
2022-09-19 14:04 ` Adhemerval Zanella Netto
2022-09-03 8:54 ` Richard Henderson
2022-09-02 20:39 ` [PATCH 10/17] string: Improve generic memchr Adhemerval Zanella
2022-09-03 3:47 ` Noah Goldstein
2022-09-19 19:17 ` Adhemerval Zanella Netto
2022-09-19 21:59 ` Noah Goldstein
2022-09-22 17:51 ` Adhemerval Zanella Netto
2022-09-02 20:39 ` [PATCH 11/17] string: Improve generic memrchr Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 12/17] hppa: Add memcopy.h Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 13/17] hppa: Add string-fzb.h and string-fzi.h Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 14/17] alpha: " Adhemerval Zanella
2022-09-02 20:39 ` [PATCH 15/17] arm: Add string-fza.h Adhemerval Zanella
2022-09-05 15:40 ` Richard Earnshaw
2022-09-05 15:50 ` Richard Earnshaw
2022-09-02 20:39 ` [PATCH 16/17] powerpc: " Adhemerval Zanella
2022-09-06 14:48 ` Paul E Murphy
2022-09-19 19:55 ` Adhemerval Zanella Netto
2022-09-02 20:39 ` [PATCH 17/17] sh: Add string-fzb.h Adhemerval Zanella
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