sysdeps/i386/bzero.c

   1 /* bzero -- set a block of memory to zero.
   2    For Intel 80x86, x>=3.
   3    Copyright (C) 1991, 1992, 1993 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
  18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  19 Cambridge, MA 02139, USA.  */
  20
  21 #include <ansidecl.h>
  22 #include <string.h>
  23 #include <memcopy.h>
  24
  25 #undef  bzero
  26
  27 #ifdef  __GNUC__
  28
  29 void
  30 DEFUN(bzero, (dstpp, len),
  31       PTR dstpp AND size_t len)
  32 {
  33   /* N.B.: This code is almost verbatim from memset.c.  */
  34
  35   unsigned long int dstp = (unsigned long int) dstpp;
  36
  37   /* This explicit register allocation
  38      improves code very much indeed.  */
  39   register op_t x asm("ax");
  40
  41   x = 0;
  42
  43   /* Clear the direction flag, so filling will move forward.  */
  44   asm volatile("cld");
  45
  46   /* This threshold value is optimal.  */
  47   if (len >= 12)
  48     {
  49       /* Adjust LEN for the bytes handled in the first loop.  */
  50       len -= (-dstp) % OPSIZ;
  51
  52       /* There are at least some bytes to set.
  53          No need to test for LEN == 0 in this alignment loop.  */
  54
  55       /* Fill bytes until DSTP is aligned on a longword boundary.  */
  56       asm volatile("rep\n"
  57                    "stosb" /* %0, %2, %3 */ :
  58                    "=D" (dstp) :
  59                    "0" (dstp), "c" ((-dstp) % OPSIZ), "a" (x) :
  60                    "cx");
  61
  62       /* Fill longwords.  */
  63       asm volatile("rep\n"
  64                    "stosl" /* %0, %2, %3 */ :
  65                    "=D" (dstp) :
  66                    "0" (dstp), "c" (len / OPSIZ), "a" (x) :
  67                    "cx");
  68       len %= OPSIZ;
  69     }
  70
  71   /* Write the last few bytes.  */
  72   asm volatile("rep\n"
  73                "stosb" /* %0, %2, %3 */ :
  74                "=D" (dstp) :
  75                "0" (dstp), "c" (len), "a" (x) :
  76                "cx");
  77 }
  78
  79 #else
  80 #include <sysdeps/generic/bzero.c>
  81 #endif