sysdeps/i386/bzero.c

   1 /* bzero -- set a block of memory to zero.  For Intel 80x86, x>=3.
   2    This file is part of the GNU C Library.
   3    Copyright (C) 1991,92,93,97,98,99, 05 Free Software Foundation, Inc.
   4    Contributed by Torbjorn Granlund (tege@sics.se).
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <string.h>
  22 #include <memcopy.h>
  23
  24 #undef  bzero
  25 #undef  __bzero
  26
  27 #ifdef  __GNUC__
  28
  29 void
  30 __bzero (dstpp, len)
  31      void *dstpp;
  32      size_t len;
  33 {
  34   /* N.B.: This code is almost verbatim from memset.c.  */
  35   int d0;
  36   unsigned long int dstp = (unsigned long int) dstpp;
  37
  38   /* This explicit register allocation
  39      improves code very much indeed.  */
  40   register op_t x asm ("ax");
  41
  42   x = 0;
  43
  44   /* Clear the direction flag, so filling will move forward.  */
  45   asm volatile ("cld");
  46
  47   /* This threshold value is optimal.  */
  48   if (len >= 12)
  49     {
  50       /* Adjust LEN for the bytes handled in the first loop.  */
  51       len -= (-dstp) % OPSIZ;
  52
  53       /* There are at least some bytes to set.
  54          No need to test for LEN == 0 in this alignment loop.  */
  55
  56       /* Fill bytes until DSTP is aligned on a longword boundary.  */
  57       asm volatile ("rep\n"
  58                     "stosb" /* %0, %2, %3 */ :
  59                     "=D" (dstp), "=c" (d0) :
  60                     "0" (dstp), "1" ((-dstp) % OPSIZ), "a" (x) :
  61                     "memory");
  62
  63       /* Fill longwords.  */
  64       asm volatile ("rep\n"
  65                     "stosl" /* %0, %2, %3 */ :
  66                     "=D" (dstp), "=c" (d0) :
  67                     "0" (dstp), "1" (len / OPSIZ), "a" (x) :
  68                     "memory");
  69       len %= OPSIZ;
  70     }
  71
  72   /* Write the last few bytes.  */
  73   asm volatile ("rep\n"
  74                 "stosb" /* %0, %2, %3 */ :
  75                 "=D" (dstp), "=c" (d0) :
  76                 "0" (dstp), "c" (len), "a" (x) :
  77                 "memory");
  78 }
  79 weak_alias (__bzero, bzero)
  80
  81 #else
  82 #include <string/bzero.c>
  83 #endif