/*
 * Copyright (C) 1991, 1993 Free Software Foundation, Inc.
 * Contributed by Torbjorn Granlund (tege@sics.se).
 *
 * NOTE: The canonical source of this file is maintained with the GNU C Library.
 * Bugs can be reported to bug-glibc@prep.ai.mit.edu.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 
 *
 * $Id: memcmp.c,v 1.1 1995/03/14 12:20:54 tom Exp $
 * $Log: memcmp.c,v $
 * Revision 1.1  1995/03/14  12:20:54  tom
 * Initial revision
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#undef  __ptr_t
#if defined (__cplusplus) || (defined (__STDC__) && __STDC__)
#define  __ptr_t  void *
#else /* Not C++ or ANSI C.  */
#undef  const
#define  const
#define  __ptr_t  char *
#endif /* C++ or ANSI C.  */

#if defined (HAVE_STRING_H) || defined (_LIBC)
#include <string.h>
#endif

#ifdef _LIBC

#include <memcopy.h>

#else  /* Not in the GNU C library.  */

#include <sys/types.h>

/*
 * Type to use for aligned memory operations.
 * This should normally be the biggest type supported by a single load
 * and store.  Must be an unsigned type.
 */

#define  op_t  unsigned long int
#define OPSIZ  (sizeof(op_t))

/*
 * Threshold value for when to enter the unrolled loops.
 */

#define  OP_T_THRES  16

/*
 * Type to use for unaligned operations.
 */

typedef unsigned char byte;

#ifndef WORDS_BIGENDIAN
#define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
#else
#define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
#endif

#endif  /* In the GNU C library.  */

#ifdef WORDS_BIGENDIAN
#define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
#else
#define CMP_LT_OR_GT(a, b) memcmp_bytes ((a), (b))
#endif

/* BE VERY CAREFUL IF YOU CHANGE THIS CODE!  */

/*
 * The strategy of this memcmp is:
 *
 * 1. Compare bytes until one of the block pointers is aligned.
 *
 * 2. Compare using memcmp_common_alignment or
 *    memcmp_not_common_alignment, regarding the alignment of the other
 *    block after the initial byte operations.  The maximum number of
 *    full words (of type op_t) are compared in this way.
 *
 * 3. Compare the few remaining bytes.
 */

#ifndef WORDS_BIGENDIAN
/*
 * memcmp_bytes -- Compare A and B bytewise in the byte order of the machine.
 * A and B are known to be different.
 * This is needed only on little-endian machines.
 */

#ifdef  __GNUC__
__inline
#endif

static int
memcmp_bytes (a, b)
  op_t a, b;
{
  long int srcp1 = (long int) &a;
  long int srcp2 = (long int) &b;
  op_t a0, b0;

  do{
    a0 = ((byte *) srcp1)[0];
    b0 = ((byte *) srcp2)[0];
    srcp1 += 1;
    srcp2 += 1;
    }
  while (a0 == b0);
  return a0 - b0;
}
#endif

/*
 * memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
 * objects (not LEN bytes!).  Both SRCP1 and SRCP2 should be aligned for
 * memory operations on `op_t's.
 */

#ifdef  __GNUC__
__inline
#endif

static int
memcmp_common_alignment (srcp1, srcp2, len)
  long int srcp1;
  long int srcp2;
  size_t len;
{
  op_t a0, a1;
  op_t b0, b1;

  switch (len % 4)
    {
    case 2:
      a0 = ((op_t *) srcp1)[0];
      b0 = ((op_t *) srcp2)[0];
      srcp1 -= 2 * OPSIZ;
      srcp2 -= 2 * OPSIZ;
      len += 2;
      goto do1;
    case 3:
      a1 = ((op_t *) srcp1)[0];
      b1 = ((op_t *) srcp2)[0];
      srcp1 -= OPSIZ;
      srcp2 -= OPSIZ;
      len += 1;
      goto do2;
    case 0:
      if (OP_T_THRES <= 3 * OPSIZ && len == 0)
        return 0;
      a0 = ((op_t *) srcp1)[0];
      b0 = ((op_t *) srcp2)[0];
      goto do3;
    case 1:
      a1 = ((op_t *) srcp1)[0];
      b1 = ((op_t *) srcp2)[0];
      srcp1 += OPSIZ;
      srcp2 += OPSIZ;
      len -= 1;
      if (OP_T_THRES <= 3 * OPSIZ && len == 0)
        goto do0;
      /* Fall through.  */
    }

  do{
    a0 = ((op_t *) srcp1)[0];
    b0 = ((op_t *) srcp2)[0];
    if (a1 != b1)
      return CMP_LT_OR_GT (a1, b1);

do3:
    a1 = ((op_t *) srcp1)[1];
    b1 = ((op_t *) srcp2)[1];
    if (a0 != b0)
      return CMP_LT_OR_GT (a0, b0);

do2:
    a0 = ((op_t *) srcp1)[2];
    b0 = ((op_t *) srcp2)[2];
    if (a1 != b1)
      return CMP_LT_OR_GT (a1, b1);

do1:
    a1 = ((op_t *) srcp1)[3];
    b1 = ((op_t *) srcp2)[3];
    if (a0 != b0)
      return CMP_LT_OR_GT (a0, b0);

    srcp1 += 4 * OPSIZ;
    srcp2 += 4 * OPSIZ;
    len -= 4;
    }
  while (len != 0);

  /*
   * This is the right position for do0.  Please don't move
   * it into the loop.
   */

do0:
  if (a1 != b1)
    return CMP_LT_OR_GT (a1, b1);
  return 0;
}

/*
 * memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
 * `op_t' objects (not LEN bytes!).  SRCP2 should be aligned for memory
 * operations on `op_t', but SRCP1 *should be unaligned*.
 */

#ifdef  __GNUC__
__inline
#endif

static int
memcmp_not_common_alignment (srcp1, srcp2, len)
  long int srcp1;
  long int srcp2;
  size_t len;
{
  op_t a0, a1, a2, a3;
  op_t b0, b1, b2, b3;
  op_t x;
  int shl, shr;

  /*
   * Calculate how to shift a word read at the memory operation
   * aligned srcp1 to make it aligned for comparison.
   */

  shl = 8 * (srcp1 % OPSIZ);
  shr = 8 * OPSIZ - shl;

  /*
   * Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
   * it points in the middle of.
   */

  srcp1 &= -OPSIZ;

  switch (len % 4)
    {
    case 2:
      a1 = ((op_t *) srcp1)[0];
      a2 = ((op_t *) srcp1)[1];
      b2 = ((op_t *) srcp2)[0];
      srcp1 -= 1 * OPSIZ;
      srcp2 -= 2 * OPSIZ;
      len += 2;
      goto do1;
    case 3:
      a0 = ((op_t *) srcp1)[0];
      a1 = ((op_t *) srcp1)[1];
      b1 = ((op_t *) srcp2)[0];
      srcp2 -= 1 * OPSIZ;
      len += 1;
      goto do2;
    case 0:
      if (OP_T_THRES <= 3 * OPSIZ && len == 0)
        return 0;
      a3 = ((op_t *) srcp1)[0];
      a0 = ((op_t *) srcp1)[1];
      b0 = ((op_t *) srcp2)[0];
      srcp1 += 1 * OPSIZ;
      goto do3;
    case 1:
      a2 = ((op_t *) srcp1)[0];
      a3 = ((op_t *) srcp1)[1];
      b3 = ((op_t *) srcp2)[0];
      srcp1 += 2 * OPSIZ;
      srcp2 += 1 * OPSIZ;
      len -= 1;
      if (OP_T_THRES <= 3 * OPSIZ && len == 0)
        goto do0;
      /* Fall through.  */
    }

  do{
    a0 = ((op_t *) srcp1)[0];
    b0 = ((op_t *) srcp2)[0];
    x = MERGE(a2, shl, a3, shr);
    if (x != b3)
      return CMP_LT_OR_GT (x, b3);

do3:
    a1 = ((op_t *) srcp1)[1];
    b1 = ((op_t *) srcp2)[1];
    x = MERGE(a3, shl, a0, shr);
    if (x != b0)
      return CMP_LT_OR_GT (x, b0);

do2:
    a2 = ((op_t *) srcp1)[2];
    b2 = ((op_t *) srcp2)[2];
    x = MERGE(a0, shl, a1, shr);
    if (x != b1)
      return CMP_LT_OR_GT (x, b1);

do1:
    a3 = ((op_t *) srcp1)[3];
    b3 = ((op_t *) srcp2)[3];
    x = MERGE(a1, shl, a2, shr);
    if (x != b2)
      return CMP_LT_OR_GT (x, b2);

    srcp1 += 4 * OPSIZ;
    srcp2 += 4 * OPSIZ;
    len -= 4;
    }
  while (len != 0);

  /*
   * This is the right position for do0.  Please don't move
   * it into the loop.
   */

do0:
  x = MERGE(a2, shl, a3, shr);
  if (x != b3)
    return CMP_LT_OR_GT (x, b3);
  return 0;
}

int
memcmp (s1, s2, len)
  const __ptr_t s1;
  const __ptr_t s2;
  size_t len;
{
  op_t a0;
  op_t b0;
  long int srcp1 = (long int) s1;
  long int srcp2 = (long int) s2;
  op_t res;

  if (len >= OP_T_THRES)
    {
    /*
     * There are at least some bytes to compare.  No need to test
     *for LEN == 0 in this alignment loop.
     */
    while (srcp2 % OPSIZ != 0)
      {
      a0 = ((byte *) srcp1)[0];
      b0 = ((byte *) srcp2)[0];
      srcp1 += 1;
      srcp2 += 1;
      res = a0 - b0;
      if (res != 0)
        return res;
      len -= 1;
      }

    /*
     * SRCP2 is now aligned for memory operations on `op_t'.
     * SRCP1 alignment determines if we can do a simple,
     * aligned compare or need to shuffle bits.
     */

    if (srcp1 % OPSIZ == 0)
      res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
    else
      res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
    if (res != 0)
      return res;

    /* Number of bytes remaining in the interval [0..OPSIZ-1].  */
    srcp1 += len & -OPSIZ;
    srcp2 += len & -OPSIZ;
    len %= OPSIZ;
    }

  /* There are just a few bytes to compare.  Use byte memory operations.  */
  while (len != 0)
    {
    a0 = ((byte *) srcp1)[0];
    b0 = ((byte *) srcp2)[0];
    srcp1 += 1;
    srcp2 += 1;
    res = a0 - b0;
    if (res != 0)
      return res;
    len -= 1;
    }

  return 0;
}