sysdeps/i386/memset.c

   1 /* Set a block of memory to some byte value.
   2    For Intel 80x86, x>=3.
   3    Copyright (C) 1991-2015 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Torbjorn Granlund (tege@sics.se).
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <http://www.gnu.org/licenses/>.  */
  20
  21 #include <string.h>
  22 #include <memcopy.h>
  23
  24 #ifdef  __GNUC__
  25
  26 #undef memset
  27
  28 void *
  29 memset (void *dstpp, int c, size_t len)
  30 {
  31   int d0;
  32   unsigned long int dstp = (unsigned long int) dstpp;
  33
  34   /* This explicit register allocation
  35      improves code very much indeed.  */
  36   register op_t x asm("ax");
  37
  38   x = (unsigned char) c;
  39
  40   /* Clear the direction flag, so filling will move forward.  */
  41   asm volatile("cld");
  42
  43   /* This threshold value is optimal.  */
  44   if (len >= 12)
  45     {
  46       /* Fill X with four copies of the char we want to fill with.  */
  47       x |= (x << 8);
  48       x |= (x << 16);
  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), "1" (len), "a" (x) :
  77                "memory");
  78
  79   return dstpp;
  80 }
  81 libc_hidden_builtin_def (memset)
  82
  83 #else
  84 #include <string/memset.c>
  85 #endif