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glibc  2.9
Defines | Typedefs | Functions
memcmp.c File Reference
#include <sys/types.h>

Go to the source code of this file.

Defines

#define const
#define __ptr_t   char *
#define op_t   unsigned long int
#define OPSIZ   (sizeof(op_t))
#define OP_T_THRES   16
#define MERGE(w0, sh_1, w1, sh_2)   (((w0) >> (sh_1)) | ((w1) << (sh_2)))
#define CMP_LT_OR_GT(a, b)   memcmp_bytes ((a), (b))

Typedefs

typedef unsigned char byte

Functions

static int memcmp_bytes (op_t, op_t)
static int memcmp_common_alignment (long, long, size_t)
static int memcmp_not_common_alignment (long, long, size_t)
int memcmp (__ptr_t s1, const __ptr_t s2, size_t len) const

Define Documentation

#define __ptr_t   char *

Definition at line 31 of file memcmp.c.

#define CMP_LT_OR_GT (   a,
  b 
)    memcmp_bytes ((a), (b))

Definition at line 76 of file memcmp.c.

#define const

Definition at line 30 of file memcmp.c.

#define MERGE (   w0,
  sh_1,
  w1,
  sh_2 
)    (((w0) >> (sh_1)) | ((w1) << (sh_2)))

Definition at line 66 of file memcmp.c.

#define op_t   unsigned long int

Definition at line 56 of file memcmp.c.

#define OP_T_THRES   16

Definition at line 60 of file memcmp.c.

#define OPSIZ   (sizeof(op_t))

Definition at line 57 of file memcmp.c.


Typedef Documentation

typedef unsigned char byte

Definition at line 63 of file memcmp.c.


Function Documentation

int memcmp ( __ptr_t  s1,
const __ptr_t  s2,
size_t  len 
) const

Definition at line 318 of file memcmp.c.

{
  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;
}

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static int memcmp_bytes ( op_t  ,
op_t   
) [static]

Definition at line 97 of file memcmp.c.

{
  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;
}
static int memcmp_common_alignment ( long  ,
long  ,
size_t   
) [static]

Definition at line 122 of file memcmp.c.

{
  op_t a0, a1;
  op_t b0, b1;

  switch (len % 4)
    {
    default: /* Avoid warning about uninitialized local variables.  */
    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;
}

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static int memcmp_not_common_alignment ( long  ,
long  ,
size_t   
) [static]

Definition at line 209 of file memcmp.c.

{
  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)
    {
    default: /* Avoid warning about uninitialized local variables.  */
    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;
}

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