gistfile1.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>


unsigned char RandomByte(unsigned char maxValue)
{
  return (unsigned char) ((unsigned long)rand() * maxValue / RAND_MAX);
}

void FillByteArrayWithUniqueValues(unsigned char *byteArray)
{
	unsigned char remainingValues[256];
	int i, lastIndex = 255;

	for (i = 0; i < 256; i++)
	{
		remainingValues[i] = i;
	}

	while (lastIndex != 0)
	{
		unsigned char b = RandomByte(lastIndex);
		byteArray[lastIndex] = remainingValues[b];
		for(i = b; i < lastIndex; i++)
		{
			remainingValues[i] = remainingValues[i+1];
		}
		lastIndex--;
	}
}


int main()
{
	unsigned char byteArray[4][256];
	int *uniqueNumbers;
	clock_t start, end;
	int i, uniqueNumbersToGenerate = 1000 * 1000, *np,  byteIndex;
	double elapsed;
	
	start = clock();

	for (i= 0; i < 4; i++)
	{
		FillByteArrayWithUniqueValues(byteArray[i]);
	}
	uniqueNumbers = (int*) malloc(sizeof(int) * uniqueNumbersToGenerate);

	np = uniqueNumbers;

	for (i = 0; i < uniqueNumbersToGenerate; i++, np++)
	{
		for (byteIndex = 0; byteIndex < 4; byteIndex++)
		{
			((unsigned char*)np)[byteIndex] = byteArray[byteIndex][(i >> (8 * byteIndex)) & 0x000000FF];
		}
	}

	end = clock();
	elapsed = (double) (end - start) / CLOCKS_PER_SEC;

	printf("Elapsed seconds %lf \n", elapsed);

}