From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: libc-alpha@sourceware.org, Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v5 10/17] string: Improve generic memchr
Date: Mon, 9 Jan 2023 17:51:29 -0300 [thread overview]
Message-ID: <6e926487-5fff-5c67-6c86-6cc38a126bf8@linaro.org> (raw)
In-Reply-To: <CAFUsyf+dbO-VEy_MugLe_EF4fmrsEKKFT797dL4xGmbwL2SR_Q@mail.gmail.com>
On 05/01/23 20:49, Noah Goldstein wrote:
> On Mon, Sep 19, 2022 at 1:05 PM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>> 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 <rth@twiddle.net>
>> ---
>> string/memchr.c | 168 +++++-------------
>> .../powerpc32/power4/multiarch/memchr-ppc32.c | 14 +-
>> .../powerpc64/multiarch/memchr-ppc64.c | 9 +-
>> 3 files changed, 48 insertions(+), 143 deletions(-)
>>
>> diff --git a/string/memchr.c b/string/memchr.c
>> index 422bcd0cd6..08d518b02d 100644
>> --- a/string/memchr.c
>> +++ b/string/memchr.c
>> @@ -1,10 +1,6 @@
>> -/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
>> +/* Scan memory for a character. Generic version
>> + 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
>> - 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 +16,65 @@
>> 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>
>> +#undef memchr
>>
>> -#include <limits.h>
>> -
>> -#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;
>> + if (__glibc_unlikely (n == 0))
>> + return NULL;
>>
>> - const unsigned char *char_ptr;
>> - const longword *longword_ptr;
>> - longword repeated_one;
>> - longword repeated_c;
>> - unsigned char c;
>> + uintptr_t s_int = (uintptr_t) s;
>>
>> - c = (unsigned char) c_in;
>> + /* Set up a word, each of whose bytes is C. */
>> + op_t repeated_c = repeat_bytes (c_in);
>> + op_t before_mask = create_mask (s_int);
>>
>> - /* 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;
>> + /* Compute the address of the last byte taking in consideration possible
>> + overflow. */
>> + const char *lbyte = sadd (s_int, n - 1);
>>
>> - longword_ptr = (const longword *) char_ptr;
>> + /* Compute the address of the word containing the last byte. */
>> + const op_t *lword = word_containing (lbyte);
>>
>> - /* All these elucidatory comments refer to 4-byte longwords,
>> - but the theory applies equally well to any size longwords. */
>> + /* 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);
>> + op_t word = (*word_ptr | before_mask) ^ (repeated_c & before_mask);
>>
>> - /* 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)
>> + while (has_eq (word, repeated_c) == 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;
>> - }
>> - }
>> + if (word_ptr == lword)
>> + return NULL;
> Inuitively making lword, lword - 1 so that normal returns don't need the extra
> null check would be faster.
Hum, I did not follow; could you explain it with more details what you mean here?
next prev parent reply other threads:[~2023-01-09 20:51 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-19 19:59 [PATCH v5 00/17] Improve generic string routines Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 01/17] Parameterize op_t from memcopy.h Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 02/17] Parameterize OP_T_THRES " Adhemerval Zanella
2022-09-20 10:49 ` Carlos O'Donell
2022-09-19 19:59 ` [PATCH v5 03/17] Add string-maskoff.h generic header Adhemerval Zanella
2022-09-20 11:43 ` Carlos O'Donell
2022-09-22 17:31 ` Adhemerval Zanella Netto
2023-01-05 22:49 ` Noah Goldstein
2023-01-05 23:26 ` Alejandro Colomar
2023-01-09 18:19 ` Adhemerval Zanella Netto
2023-01-09 18:02 ` Adhemerval Zanella Netto
2022-09-19 19:59 ` [PATCH v5 04/17] Add string vectorized find and detection functions Adhemerval Zanella
2023-01-05 22:53 ` Noah Goldstein
2023-01-09 18:51 ` Adhemerval Zanella Netto
2023-01-05 23:04 ` Noah Goldstein
2023-01-09 19:34 ` Adhemerval Zanella Netto
2022-09-19 19:59 ` [PATCH v5 05/17] string: Improve generic strlen Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 06/17] string: Improve generic strnlen Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 07/17] string: Improve generic strchr Adhemerval Zanella
2023-01-05 23:09 ` Noah Goldstein
2023-01-05 23:19 ` Noah Goldstein
2023-01-09 19:39 ` Adhemerval Zanella Netto
2022-09-19 19:59 ` [PATCH v5 08/17] string: Improve generic strchrnul Adhemerval Zanella
2023-01-05 23:17 ` Noah Goldstein
2023-01-09 20:35 ` Adhemerval Zanella Netto
2023-01-09 20:49 ` Richard Henderson
2023-01-09 20:59 ` Noah Goldstein
2023-01-09 21:01 ` Noah Goldstein
2023-01-09 23:33 ` Richard Henderson
2023-01-10 14:18 ` Adhemerval Zanella Netto
2023-01-10 16:24 ` Richard Henderson
2023-01-10 17:16 ` Noah Goldstein
2023-01-10 18:19 ` Adhemerval Zanella Netto
2023-01-10 17:17 ` Noah Goldstein
2023-01-10 18:16 ` Adhemerval Zanella Netto
2022-09-19 19:59 ` [PATCH v5 09/17] string: Improve generic strcmp Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 10/17] string: Improve generic memchr Adhemerval Zanella
2023-01-05 23:47 ` Noah Goldstein
2023-01-09 20:50 ` Adhemerval Zanella Netto
2023-01-05 23:49 ` Noah Goldstein
2023-01-09 20:51 ` Adhemerval Zanella Netto [this message]
2023-01-09 21:26 ` Noah Goldstein
2023-01-10 14:33 ` Adhemerval Zanella Netto
2022-09-19 19:59 ` [PATCH v5 11/17] string: Improve generic memrchr Adhemerval Zanella
2023-01-05 23:51 ` Noah Goldstein
2022-09-19 19:59 ` [PATCH v5 12/17] hppa: Add memcopy.h Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 13/17] hppa: Add string-fzb.h and string-fzi.h Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 14/17] alpha: " Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 15/17] arm: Add string-fza.h Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 16/17] powerpc: " Adhemerval Zanella
2022-09-19 19:59 ` [PATCH v5 17/17] sh: Add string-fzb.h Adhemerval Zanella
2022-12-05 17:07 ` [PATCH v5 00/17] Improve generic string routines Xi Ruoyao
2023-01-05 21:56 ` Adhemerval Zanella Netto
2023-01-05 23:52 ` Noah Goldstein
2023-01-06 13:43 ` Adhemerval Zanella Netto
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