Program to check whether the compiler converts a given floating point number to the IEEE 754 specification. - February 25, 2011

ieee754.c

/*
 * ieee754.c
 *
 * Program to check whether the compiler converts a given floating point number
 * to the IEEE 754 specification.
 *
 * Original Authors: Mohammed Hashir and Ashwin Jacob
 * This is a slightly modified and improved version by
 *
 * Kartik Singhal - B090566CS
 *
 * Special thanks to the original authors.
*/

#include <stdio.h>
#include <math.h>

void strev(int *s, int l)
{
	int tmp;
	int f = 0;
	while (f < l) {
		tmp = s[f];
		s[f] = s[l];
		s[l] = tmp;
		f++;
		l--;
	}
}

int main()
{
	float fnum, *z;
	int a[33], c[24], b[8];
	int i, k, m, q=0, s;
	for(k = 30; k >= 20; k--)
		q = q | (1<<k);
	z = (float*)&q;
	float p;
	p = 0.0;
	m = 0;
	printf("Enter a floating point number: ");
	scanf("%f", &fnum);
	int *ptr=(int*)&fnum;
	i = *ptr;
	for(k = 0; k < 32; k++)
	{
		if(i & (1<<k))
			a[k] = 1;
		else
			a[k] = 0;
	}
	strev(a, 31);

	s = a[0];
	for(k = 0; k<8; k++)
		b[k] = a[k+1];
	for(k = 0; k<23; k++)
		c[k] = a[k+9];

	printf("\nSign Bit (31): %d", s);
	printf("\nExponent Field (30 - 23): ");
	for(k = 0; k<8; k++)
		printf("%d", b[k]);
	printf("\nSignificand (22 - 0): ");
	for(k = 0; k<23; k++)
		printf("%d", c[k]);

	strev(b, 7);
	strev(c, 22);
	for(k = 0; k<8; k++)
	{
		if(b[k] == 1)
			m = m+pow(2, k);
	}
	for(k = 0; k<23; k++)
	{
		if(c[k] == 1)
			p = p+pow(2, k-22);
	}

	printf("\n\nDecimal value of exponent field: %d", m);
	printf("\n");

	if(m == 0 && p == 0.0)
		printf("\nZero\n");
	else if(m == 0 && p != 0.0)
		printf("\nDenormalised number\n");
	else if(m > 0 && m < 255)
		printf("\nNormalised number\n");
	else if(m == 255 && p == 0.0 && q <= (3.40282367 * pow(10, 38)))
		printf("\nInfinity\n");
	else if(m == 255 && q != 0.0)
	printf("\nNaN\n");

	return 0;
}

/*

Sample Output
=============

Output verified from the IEEE-754 floating point converter at http://babbage.cs.qc.edu/IEEE-754/Decimal.html

kartik@PlatiniumLight:/media/Voyager$ gcc ieee754.c -lm

kartik@PlatiniumLight:/media/Voyager$ ./a.out 
Enter a floating point number: 42

Sign Bit (31): 0
Exponent Field (30 - 23): 10000100
Significand (22 - 0): 01010000000000000000000

Decimal value of exponent field: 132

Normalised number

kartik@PlatiniumLight:/media/Voyager$ ./a.out 
Enter a floating point number: -42.25

Sign Bit (31): 1
Exponent Field (30 - 23): 10000100
Significand (22 - 0): 01010010000000000000000

Decimal value of exponent field: 132

Normalised number

kartik@PlatiniumLight:/media/Voyager$

*/