GNU C Library master sources branch master updated. glibc-2.24-468-g3038145

[wilco at sourceware dot org]

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=3038145ca2355d8fde8c21448961c1be1ed5c287

commit 3038145ca2355d8fde8c21448961c1be1ed5c287
Author: Wilco Dijkstra <wdijkstr@arm.com>
Date:   Wed Dec 14 13:16:13 2016 +0000

    Improve generic rawmemchr for targets that don't have an
    assembler version by tailcalling memchr with the maximum size.
    If a target has an optimized memchr this is significantly faster,
    if not, then this makes little difference.
    Also optimize the special case of zero to use strlen as this is
    typically faster than memchr.
    
    	* string/rawmemchr.c (RAWMEMCHR): Use faster memchr/strlen.

diff --git a/ChangeLog b/ChangeLog
index 25b50c3..15085f5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2015-12-14  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* string/rawmemchr.c (RAWMEMCHR): Use faster memchr/strlen.
+
 2016-12-14  Joseph Myers  <joseph@codesourcery.com>
 
 	* scripts/build-many-glibcs.py (Context.checkout): Default Linux
diff --git a/string/rawmemchr.c b/string/rawmemchr.c
index fa3176d..1a146af 100644
--- a/string/rawmemchr.c
+++ b/string/rawmemchr.c
@@ -1,10 +1,5 @@
 /* Copyright (C) 1991-2016 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
@@ -20,157 +15,19 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#ifdef HAVE_CONFIG_H
-#include <config.h>
-#endif
-
-#undef __ptr_t
-#define __ptr_t void *
-
-#if defined (_LIBC)
-# include <string.h>
-# include <memcopy.h>
-# include <stdlib.h>
-#endif
-
-#if defined (HAVE_LIMITS_H) || defined (_LIBC)
-# include <limits.h>
-#endif
-
-#define LONG_MAX_32_BITS 2147483647
-
-#ifndef LONG_MAX
-#define LONG_MAX LONG_MAX_32_BITS
-#endif
-
-#include <sys/types.h>
-
-#undef memchr
+#include <string.h>
 
 #ifndef RAWMEMCHR
 # define RAWMEMCHR __rawmemchr
 #endif
 
 /* Find the first occurrence of C in S.  */
-__ptr_t
-RAWMEMCHR (const __ptr_t s, int c_in)
+void *
+RAWMEMCHR (const void *s, int c)
 {
-  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)
-      return (__ptr_t) 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 LONG_MAX > LONG_MAX_32_BITS
-  charmask |= charmask << 32;
-#endif
-
-  /* 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 (1)
-    {
-      /* 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.
-
-	 3) But wait!  Aren't we looking for C, not 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++ ^ charmask;
-
-      /* 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)
-	{
-	  /* Which of the bytes was C?  If none of them were, it was
-	     a misfire; continue the search.  */
-
-	  const unsigned char *cp = (const unsigned char *) (longword_ptr - 1);
-
-	  if (cp[0] == c)
-	    return (__ptr_t) cp;
-	  if (cp[1] == c)
-	    return (__ptr_t) &cp[1];
-	  if (cp[2] == c)
-	    return (__ptr_t) &cp[2];
-	  if (cp[3] == c)
-	    return (__ptr_t) &cp[3];
-#if LONG_MAX > 2147483647
-	  if (cp[4] == c)
-	    return (__ptr_t) &cp[4];
-	  if (cp[5] == c)
-	    return (__ptr_t) &cp[5];
-	  if (cp[6] == c)
-	    return (__ptr_t) &cp[6];
-	  if (cp[7] == c)
-	    return (__ptr_t) &cp[7];
-#endif
-	}
-    }
+  if (c != '\0')
+    return memchr (s, c, (size_t)-1);
+  return (char *)s + strlen (s);
 }
 libc_hidden_def (__rawmemchr)
 weak_alias (__rawmemchr, rawmemchr)

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog          |    4 +
 string/rawmemchr.c |  155 ++--------------------------------------------------
 2 files changed, 10 insertions(+), 149 deletions(-)


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