From: Noah Goldstein <goldstein.w.n@gmail.com>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: libc-alpha@sourceware.org,
Richard Henderson <richard.henderson@linaro.org>,
Jeff Law <jeffreyalaw@gmail.com>, Xi Ruoyao <xry111@xry111.site>
Subject: Re: [PATCH v12 12/31] string: Improve generic strnlen with memchr
Date: Fri, 3 Feb 2023 17:27:51 -0600 [thread overview]
Message-ID: <CAFUsyfK27iuMGKcxyU18wqbV+ErH0DaoyqrbtB1-dKT90Xmxvg@mail.gmail.com> (raw)
In-Reply-To: <20230202181149.2181553-13-adhemerval.zanella@linaro.org>
On Thu, Feb 2, 2023 at 12:12 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> It also cleanups the multiple inclusion by leaving the ifunc
> implementation to undef the weak_alias and libc_hidden_def.
>
> Co-authored-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> string/strnlen.c | 137 +-----------------
> sysdeps/i386/i686/multiarch/strnlen-c.c | 14 +-
> .../power4/multiarch/strnlen-ppc32.c | 14 +-
> sysdeps/s390/strnlen-c.c | 14 +-
> 4 files changed, 27 insertions(+), 152 deletions(-)
>
> diff --git a/string/strnlen.c b/string/strnlen.c
> index 6ff294eab1..dc23354ec8 100644
> --- a/string/strnlen.c
> +++ b/string/strnlen.c
> @@ -1,10 +1,6 @@
> /* Find the length of STRING, but scan at most MAXLEN characters.
> Copyright (C) 1991-2023 Free Software Foundation, Inc.
>
> - Based on strlen written by Torbjorn Granlund (tege@sics.se),
> - with help from Dan Sahlin (dan@sics.se);
> - commentary by Jim Blandy (jimb@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 License as
> published by the Free Software Foundation; either version 2.1 of the
> @@ -20,7 +16,6 @@
> not, see <https://www.gnu.org/licenses/>. */
>
> #include <string.h>
> -#include <stdlib.h>
>
> /* Find the length of S, but scan at most MAXLEN characters. If no
> '\0' terminator is found in that many characters, return MAXLEN. */
> @@ -32,134 +27,12 @@
> size_t
> __strnlen (const char *str, size_t maxlen)
> {
> - const char *char_ptr, *end_ptr = str + maxlen;
> - const unsigned long int *longword_ptr;
> - unsigned long int longword, himagic, lomagic;
> -
> - if (maxlen == 0)
> - return 0;
> -
> - if (__glibc_unlikely (end_ptr < str))
> - end_ptr = (const char *) ~0UL;
> -
> - /* 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 = str; ((unsigned long int) char_ptr
> - & (sizeof (longword) - 1)) != 0;
> - ++char_ptr)
> - if (*char_ptr == '\0')
> - {
> - if (char_ptr > end_ptr)
> - char_ptr = end_ptr;
> - return char_ptr - str;
> - }
> -
> - /* 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. */
> - himagic = 0x80808080L;
> - lomagic = 0x01010101L;
> - if (sizeof (longword) > 4)
> - {
> - /* 64-bit version of the magic. */
> - /* Do the shift in two steps to avoid a warning if long has 32 bits. */
> - himagic = ((himagic << 16) << 16) | himagic;
> - lomagic = ((lomagic << 16) << 16) | lomagic;
> - }
> - 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. */
> - while (longword_ptr < (unsigned long int *) end_ptr)
> - {
> - /* 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. */
> -
> - longword = *longword_ptr++;
> -
> - if ((longword - lomagic) & himagic)
> - {
> - /* Which of the bytes was the zero? If none of them were, it was
> - a misfire; continue the search. */
> -
> - const char *cp = (const char *) (longword_ptr - 1);
> -
> - char_ptr = cp;
> - if (cp[0] == 0)
> - break;
> - char_ptr = cp + 1;
> - if (cp[1] == 0)
> - break;
> - char_ptr = cp + 2;
> - if (cp[2] == 0)
> - break;
> - char_ptr = cp + 3;
> - if (cp[3] == 0)
> - break;
> - if (sizeof (longword) > 4)
> - {
> - char_ptr = cp + 4;
> - if (cp[4] == 0)
> - break;
> - char_ptr = cp + 5;
> - if (cp[5] == 0)
> - break;
> - char_ptr = cp + 6;
> - if (cp[6] == 0)
> - break;
> - char_ptr = cp + 7;
> - if (cp[7] == 0)
> - break;
> - }
> - }
> - char_ptr = end_ptr;
> - }
> -
> - if (char_ptr > end_ptr)
> - char_ptr = end_ptr;
> - return char_ptr - str;
> + const char *found = memchr (str, '\0', maxlen);
> + return found ? found - str : maxlen;
> }
> +
> #ifndef STRNLEN
> -libc_hidden_def (__strnlen)
> weak_alias (__strnlen, strnlen)
> -#endif
> +libc_hidden_def (__strnlen)
> libc_hidden_def (strnlen)
> +#endif
> diff --git a/sysdeps/i386/i686/multiarch/strnlen-c.c b/sysdeps/i386/i686/multiarch/strnlen-c.c
> index 351e939a93..beb0350d53 100644
> --- a/sysdeps/i386/i686/multiarch/strnlen-c.c
> +++ b/sysdeps/i386/i686/multiarch/strnlen-c.c
> @@ -1,10 +1,10 @@
> #define STRNLEN __strnlen_ia32
> +#include <string/strnlen.c>
> +
> #ifdef SHARED
> -# undef libc_hidden_def
> -# define libc_hidden_def(name) \
> - __hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32); \
> - strong_alias (__strnlen_ia32, __strnlen_ia32_1); \
> - __hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1);
> +/* Alias for internal symbol to avoid PLT generation, it redirects the
> + libc_hidden_def (__strnlen/strlen) to default implementation. */
> +__hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32);
> +strong_alias (__strnlen_ia32, __strnlen_ia32_1);
> +__hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1);
> #endif
> -
> -#include "string/strnlen.c"
> diff --git a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c
> index 957b9b99e8..2ca1cd7181 100644
> --- a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c
> +++ b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c
> @@ -17,12 +17,12 @@
> <https://www.gnu.org/licenses/>. */
>
> #define STRNLEN __strnlen_ppc
> +#include <string/strnlen.c>
> +
> #ifdef SHARED
> -# undef libc_hidden_def
> -# define libc_hidden_def(name) \
> - __hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \
> - strong_alias (__strnlen_ppc, __strnlen_ppc_1); \
> - __hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1);
> +/* Alias for internal symbol to avoid PLT generation, it redirects the
> + libc_hidden_def (__strnlen/strlen) to default implementation. */
> +__hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \
> +strong_alias (__strnlen_ppc, __strnlen_ppc_1); \
> +__hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1);
> #endif
> -
> -#include <string/strnlen.c>
> diff --git a/sysdeps/s390/strnlen-c.c b/sysdeps/s390/strnlen-c.c
> index 172fcc7caa..95156a0ff5 100644
> --- a/sysdeps/s390/strnlen-c.c
> +++ b/sysdeps/s390/strnlen-c.c
> @@ -21,14 +21,16 @@
> #if HAVE_STRNLEN_C
> # if HAVE_STRNLEN_IFUNC
> # define STRNLEN STRNLEN_C
> +# endif
> +
> +# include <string/strnlen.c>
> +
> +# if HAVE_STRNLEN_IFUNC
> # if defined SHARED && IS_IN (libc)
> -# undef libc_hidden_def
> -# define libc_hidden_def(name) \
> - __hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c); \
> - strong_alias (__strnlen_c, __strnlen_c_1); \
> - __hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1);
> +__hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c);
> +strong_alias (__strnlen_c, __strnlen_c_1);
> +__hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1);
> # endif
> # endif
>
> -# include <string/strnlen.c>
> #endif
> --
> 2.34.1
>
LGTM.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
next prev parent reply other threads:[~2023-02-03 23:28 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-02 18:11 [PATCH v12 00/31] Improve generic string routines Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 01/31] Parameterize op_t from memcopy.h Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 02/31] Parameterize OP_T_THRES " Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 03/31] Add string vectorized find and detection functions Adhemerval Zanella
2023-02-03 0:24 ` Richard Henderson
2023-02-03 12:39 ` Adhemerval Zanella Netto
2023-02-03 13:40 ` Adhemerval Zanella Netto
2023-02-04 2:54 ` Richard Henderson
2023-02-02 18:11 ` [PATCH v12 04/31] string: Improve generic strlen Adhemerval Zanella
2023-02-03 23:23 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 05/31] string: Improve generic strchrnul Adhemerval Zanella
2023-02-03 23:23 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 06/31] string: Improve generic strchr Adhemerval Zanella
2023-02-03 23:24 ` Noah Goldstein
2023-02-04 2:58 ` Richard Henderson
2023-02-06 13:07 ` Adhemerval Zanella Netto
2023-02-02 18:11 ` [PATCH v12 07/31] string: Improve generic strcmp Adhemerval Zanella
2023-02-03 23:25 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 08/31] string: Improve generic strncmp Adhemerval Zanella
2023-02-03 0:34 ` Richard Henderson
2023-02-21 9:28 ` Szabolcs Nagy
2023-02-21 12:24 ` Adhemerval Zanella Netto
2023-02-02 18:11 ` [PATCH v12 09/31] string: Improve generic stpcpy Adhemerval Zanella
2023-02-03 23:26 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 10/31] string: Improve generic strcpy Adhemerval Zanella
2023-02-03 23:26 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 11/31] string: Improve generic memchr Adhemerval Zanella
2023-02-03 23:26 ` Noah Goldstein
2023-02-02 18:11 ` [PATCH v12 12/31] string: Improve generic strnlen with memchr Adhemerval Zanella
2023-02-03 23:27 ` Noah Goldstein [this message]
2023-02-02 18:11 ` [PATCH v12 13/31] string: Improve generic memrchr Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 14/31] string: Improve generic strrchr with memrchr and strlen Adhemerval Zanella
2023-02-04 3:06 ` Richard Henderson
2023-02-06 14:01 ` Adhemerval Zanella Netto
2023-02-02 18:11 ` [PATCH v12 15/31] hppa: Add memcopy.h Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 16/31] hppa: Add string-fza.h, string-fzc.h, and string-fzi.h Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 17/31] alpha: Add string-fza, string-fzb.h, string-fzi.h, and string-shift.h Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 18/31] arm: Add string-fza.h Adhemerval Zanella
2023-02-20 13:24 ` Szabolcs Nagy
2023-02-20 13:45 ` Szabolcs Nagy
2023-02-20 14:01 ` Adhemerval Zanella Netto
2023-02-20 16:12 ` Szabolcs Nagy
2023-02-02 18:11 ` [PATCH v12 19/31] powerpc: " Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 20/31] sh: Add string-fzb.h Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 21/31] riscv: Add string-fza.h and string-fzi.h Adhemerval Zanella
2023-02-03 19:47 ` Noah Goldstein
2023-02-06 16:14 ` Adhemerval Zanella Netto
2023-02-02 18:11 ` [PATCH v12 22/31] string: Hook up the default implementation on test-strlen Adhemerval Zanella
2023-02-03 23:30 ` Noah Goldstein
2023-02-06 17:36 ` Adhemerval Zanella Netto
2023-02-02 18:11 ` [PATCH v12 23/31] string: Hook up the default implementation on test-strnlen Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 24/31] string: Hook up the default implementation on test-strchr Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 25/31] string: Hook up the default implementation on test-strcmp Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 26/31] string: Hook up the default implementation on test-strncmp Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 27/31] string: Hook up the default implementation on test-stpcpy Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 28/31] string: Hook up the default implementation on test-strcpy Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 29/31] string: Hook up the default implementation on test-memchr Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 30/31] string: Hook up the default implementation on test-memrchr Adhemerval Zanella
2023-02-02 18:11 ` [PATCH v12 31/31] string: Hook up the default implementation on test-strrchr Adhemerval Zanella
2023-02-03 1:55 ` Richard Henderson
2023-02-02 18:17 ` [PATCH v12 00/31] Improve generic string routines Adhemerval Zanella Netto
2023-02-03 13:18 [PATCH v12 12/31] string: Improve generic strnlen with memchr Wilco Dijkstra
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