UCR CS 122B, Adv. Embedded and Real Time Systems 
Homework 3
Prof. Frank Vahid

1. Create a straightforward "naive" C routine for reversing the bits of a 
   32-bit integer, using masks and shifts. Compare the naive routine to
   the fast bit reversal approach in the code below. Clearly explain why
   the approach below is faster.

   Note: an important part of embedded system design is not just creating
   code or designs, but being to understand existing code, and understanding
   its strengths and weaknesses.

Turn in the assignment electronically. Name your file 
hw3_firstname_lastname.txt.


----


/*-----------------------------------------------------------------------
//  file: brev.c
//
//  Copyright (c) 1994 Motorola, Inc. All Rights Reserved.

//-----------------------------------------------------------------------
 */

#define LOOPS 1
/* #define	LOOPS	89000 */
#include "Powerstone.h"
#ifdef STATIC_SIZE
unsigned long   src[1] = {0};
unsigned long   dst[1];
#else
unsigned long	src[80] =
{
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x12345678,0x12345678,0x12345678,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x12345678,0x12345678,0x12345678,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x12345678,0x12345678,0x12345678,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x12345678,0x12345678,0x12345678,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x12345678,0x12345678,0x12345678,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x10101010,0x12345678,0x10101010,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x10101010,0x12345678,0x10101010,0x12345678,
	0x00005678,0x12340000,0x02040608,0x00000001,
	0x10101010,0x12345678,0x10101010,0x12345678,
	0
};

unsigned long	dst[80];
#endif

int main()
{
	int		i;
	unsigned long	*s, *d;
	unsigned long	x;

	INIT_BOARD();
   do {
	START_TIMING();

	for (i = 0 ; i < LOOPS ; i++)
	{	for (s = src, d = dst ; *s ; s += 4, d += 4)
		{	x = s[0];
			x =  (x >>16)               |  (x <<16);
			x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
			x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
			x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
			x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
			d[0] = x;
			x = s[1];
			x =  (x >>16)               |  (x <<16);
			x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
			x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
			x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
			x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
			d[1] = x;
			x = s[2];
			x =  (x >>16)               |  (x <<16);
			x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
			x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
			x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
			x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
			d[2] = x;
			x = s[3];
			x =  (x >>16)               |  (x <<16);
			x = ((x >> 8) & 0x00ff00ff) | ((x << 8) & 0xff00ff00);
			x = ((x >> 4) & 0x0f0f0f0f) | ((x << 4) & 0xf0f0f0f0);
			x = ((x >> 2) & 0x33333333) | ((x << 2) & 0xcccccccc);
			x = ((x >> 1) & 0x55555555) | ((x << 1) & 0xaaaaaaaa);
			d[3] = x;
		}
	}

	END_TIMING();
   } while (PROFILE==0);

	exit(0);
}