sysdeps/i386/memset.c

   1 /* Set a block of memory to some byte value.
   2    For Intel 80x86, x>=3.
   3    Copyright (C) 1991, 1992, 1993, 1997 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 Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    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    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <string.h>
  22 #include <memcopy.h>
  23
  24 #ifdef  __GNUC__
  25
  26 void *
  27 memset (void *dstpp, int c, size_t len)
  28 {
  29   unsigned long int dstp = (unsigned long int) dstpp;
  30
  31   /* This explicit register allocation
  32      improves code very much indeed.  */
  33   register op_t x asm("ax");
  34
  35   x = (unsigned char) c;
  36
  37   /* Clear the direction flag, so filling will move forward.  */
  38   asm volatile("cld");
  39
  40   /* This threshold value is optimal.  */
  41   if (len >= 12)
  42     {
  43       /* Fill X with four copies of the char we want to fill with.  */
  44       x |= (x << 8);
  45       x |= (x << 16);
  46
  47       /* Adjust LEN for the bytes handled in the first loop.  */
  48       len -= (-dstp) % OPSIZ;
  49
  50       /* There are at least some bytes to set.
  51          No need to test for LEN == 0 in this alignment loop.  */
  52
  53       /* Fill bytes until DSTP is aligned on a longword boundary.  */
  54       asm volatile("rep\n"
  55                    "stosb" /* %0, %2, %3 */ :
  56                    "=D" (dstp) :
  57                    "0" (dstp), "c" ((-dstp) % OPSIZ), "a" (x) :
  58                    "cx");
  59
  60       /* Fill longwords.  */
  61       asm volatile("rep\n"
  62                    "stosl" /* %0, %2, %3 */ :
  63                    "=D" (dstp) :
  64                    "0" (dstp), "c" (len / OPSIZ), "a" (x) :
  65                    "cx");
  66       len %= OPSIZ;
  67     }
  68
  69   /* Write the last few bytes.  */
  70   asm volatile("rep\n"
  71                "stosb" /* %0, %2, %3 */ :
  72                "=D" (dstp) :
  73                "0" (dstp), "c" (len), "a" (x) :
  74                "cx");
  75
  76   return dstpp;
  77 }
  78
  79 #else
  80 #include <sysdeps/generic/memset.c>
  81 #endif