C / C++ / MFC

*b = (int*) malloc ( n * sizeof(int)); 

#include "stdio.h"

void ByteSwap4_c(int n, int *a);
void ByteSwap4_asm(int n, int *a);

void ByteSwap4(int n, int *a)
{
  int i;
  int *b = (int*) malloc ( n * sizeof(int));
  for (i=0; i<n; ++i) 
	  b[i]=a[i];

  ByteSwap4_asm(n,a);
  ByteSwap4_c(n,b);

  for (i=0; i<n; ++i) 
  {
    if (a[i] != b[i]) 
	{
      printf("a[%d] (0x%08X) != b[%d] (0x%08X)\n",i,a[i],i,b[i]);
      exit(1);
    }
  }

  free(b);
}

void test4(int n, int *a, int *b)
{
  int i;
  ByteSwap4(n,a);
  for (i=0; i<n; ++i) {
    if (a[i] != b[i]) {
      printf("a[%d] (0x%08X) != b[%d] (0x%08X)\n",i,a[i],i,b[i]);
      exit(1);
    }
  }
}

int main()
{
  static int a[4]={0x01020304, 0xa0b0c0d0, 0xabdcef12, 0x12345678};
  static int b[4]={0x04030201, 0xd0c0b0a0, 0x12efdcab, 0x78563412};

  test4(4,a,b);

  printf("all tests pass\n");
}

void ByteSwap4_c(int n, int *a)
{
  int i;
  for (i=0; i<n; ++i) 
  {
    /* byte swap a[i] */
    int tmp=a[i];
    int pmt;
    ((char*)(&pmt))[3]=((char*)(&tmp))[0];
    ((char*)(&pmt))[2]=((char*)(&tmp))[1]; 
    ((char*)(&pmt))[1]=((char*)(&tmp))[2];
    ((char*)(&pmt))[0]=((char*)(&tmp))[3];

    a[i]=pmt;
  }
}