glibc/sysdeps/tile/tilepro/memset.c

/* Copyright (C) 2011 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <http://www.gnu.org/licenses/>.  */

#include <string.h>
#include <stdint.h>
#include <arch/chip.h>

void *
__memset (void *s, int c, size_t n)
{
  uint32_t *out32;
  int n32;
  uint32_t v16, v32;
  uint8_t *out8 = s;
  int to_align32;

  /* Experimentation shows that a trivial tight loop is a win up until
     around a size of 20, where writing a word at a time starts to win.  */
#define BYTE_CUTOFF 20

#if BYTE_CUTOFF < 3
  /* This must be at least at least this big, or some code later
     on doesn't work.  */
# error "BYTE_CUTOFF is too small."
#endif

  if (n < BYTE_CUTOFF)
    {
      /* Strangely, this turns out to be the tightest way to write
         this loop.  */
      if (n != 0)
        {
          do
            {
              /* Strangely, combining these into one line performs worse.  */
              *out8 = c;
              out8++;
            }
          while (--n != 0);
        }

      return s;
    }

  /* Align 'out8'. We know n >= 3 so this won't write past the end. */
  while (((uintptr_t) out8 & 3) != 0)
    {
      *out8++ = c;
      --n;
    }

  /* Align 'n'. */
  while (n & 3)
    out8[--n] = c;

  out32 = (uint32_t *) out8;
  n32 = n >> 2;

  /* Tile input byte out to 32 bits. */
  v16 = __insn_intlb (c, c);
  v32 = __insn_intlh (v16, v16);

  /* This must be at least 8 or the following loop doesn't work. */
#define CACHE_LINE_SIZE_IN_WORDS (CHIP_L2_LINE_SIZE() / 4)

  /* Determine how many words we need to emit before the 'out32'
     pointer becomes aligned modulo the cache line size.  */
  to_align32 = (-((uintptr_t) out32 >> 2)) & (CACHE_LINE_SIZE_IN_WORDS - 1);

  /* Only bother aligning and using wh64 if there is at least one full
     cache line to process.  This check also prevents overrunning the
     end of the buffer with alignment words.  */
  if (to_align32 <= n32 - CACHE_LINE_SIZE_IN_WORDS)
    {
      int lines_left;

      /* Align out32 mod the cache line size so we can use wh64. */
      n32 -= to_align32;
      for (; to_align32 != 0; to_align32--)
        {
          *out32 = v32;
          out32++;
        }

      /* Use unsigned divide to turn this into a right shift. */
      lines_left = (unsigned) n32 / CACHE_LINE_SIZE_IN_WORDS;

      do
        {
          /* Only wh64 a few lines at a time, so we don't exceed the
             maximum number of victim lines.  */
          int x = ((lines_left < CHIP_MAX_OUTSTANDING_VICTIMS ())? lines_left
                   : CHIP_MAX_OUTSTANDING_VICTIMS ());
          uint32_t *wh = out32;
          int i = x;
          int j;

          lines_left -= x;

          do
            {
              __insn_wh64 (wh);
              wh += CACHE_LINE_SIZE_IN_WORDS;
            }
          while (--i);

          for (j = x * (CACHE_LINE_SIZE_IN_WORDS / 4); j != 0; j--)
            {
              *out32++ = v32;
              *out32++ = v32;
              *out32++ = v32;
              *out32++ = v32;
            }
        }
      while (lines_left != 0);

      /* We processed all full lines above, so only this many words
         remain to be processed.  */
      n32 &= CACHE_LINE_SIZE_IN_WORDS - 1;
    }

  /* Now handle any leftover values. */
  if (n32 != 0)
    {
      do
        {
          *out32 = v32;
          out32++;
        }
      while (--n32 != 0);
    }

  return s;
}
weak_alias (__memset, memset)
libc_hidden_builtin_def (memset)