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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


  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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