glibc/sysdeps/tile/memset.c

/* Copyright (C) 2011-2018 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 <arch/chip.h>
#include <string.h>
#include <stdint.h>
#include "string-endian.h"

void * inhibit_loop_to_libcall
__memset (void *s, int c, size_t n)
{
  uint64_t *out64;
  int n64, to_align64;
  uint64_t v64;
  uint8_t *out8 = s;

  /* 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 < 7
  /* 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 >= 7 so this won't write past the end.  */
  while (((uintptr_t) out8 & 7) != 0)
    {
      *out8++ = c;
      --n;
    }

  /* Align 'n'. */
  while (n & 7)
    out8[--n] = c;

  out64 = (uint64_t *) out8;
  n64 = n >> 3;

  /* Tile input byte out to 64 bits. */
  v64 = copy_byte(c);

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

  /* Determine how many words we need to emit before the 'out32'
     pointer becomes aligned modulo the cache line size.  */
  to_align64 = (-((uintptr_t) out64 >> 3)) &
    (CACHE_LINE_SIZE_IN_DOUBLEWORDS - 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_align64 <= n64 - CACHE_LINE_SIZE_IN_DOUBLEWORDS)
    {
      int lines_left;

      /* Align out64 mod the cache line size so we can use wh64. */
      n64 -= to_align64;
      for (; to_align64 != 0; to_align64--)
        {
          *out64 = v64;
          out64++;
        }

      /* Use unsigned divide to turn this into a right shift. */
      lines_left = (unsigned) n64 / CACHE_LINE_SIZE_IN_DOUBLEWORDS;

      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 ());
          uint64_t *wh = out64;
          int i = x;
          int j;

          lines_left -= x;

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

          for (j = x * (CACHE_LINE_SIZE_IN_DOUBLEWORDS / 4); j != 0; j--)
            {
              *out64++ = v64;
              *out64++ = v64;
              *out64++ = v64;
              *out64++ = v64;
            }
        }
      while (lines_left != 0);

      /* We processed all full lines above, so only this many
         words remain to be processed.  */
      n64 &= CACHE_LINE_SIZE_IN_DOUBLEWORDS - 1;
    }

  /* Now handle any leftover values. */
  if (n64 != 0)
    {
      do
        {
          *out64 = v64;
          out64++;
        }
      while (--n64 != 0);
    }

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