功能：互轉浮點數與二進制表示法
/* ieee754.c
* Author: Aaron Liao (http://applezulab.netdpi.net)
* Last updated: 2010/12/29
* IEEE754 sample code
* LICENSE: GPL
* 32 bits: [1][8][23]
* 64 bits: [1][11][52]
*/
#include <strings.h>
#include <string.h>
#include <stdio.h>
int ieee754(char *data, double real)
{
int exp=0, i=0, exp_tmp;
double cal, frag_tmp;
char buf[32];
bzero(buf, sizeof(buf));
cal = real;
/* get sign */
if( cal < 0 ){
buf[0] = 1;
cal *= (double) -1;
} else {
buf[0] = 0;
}
/* get exp */
while( cal >= 1.0 ) {
cal /= 2;
exp++;
}
for( i=8, exp_tmp=1; i>0; i--){
if( (exp & exp_tmp) ) {
buf[i] = 1;
} else {
buf[i] = 0;
}
exp_tmp *=2 ;
}
/* get fraction */
for(i=9, frag_tmp = (double) 1/2; i< 32; i++) {
if( (cal - frag_tmp) >= 0 ){
buf[i] = 1;
cal = (double) cal - (double) frag_tmp;
} else {
buf[i] = 0;
}
frag_tmp /= (double) 2;
}
/* To ascii */
for(i=0; i<32; i++) {
buf[i] += '0';
}
strncpy(data, buf, 32);
return 0;
}
double rev_ieee754(char *buf)
{
int exp=0, i=0, exp_tmp, sign;
double real, frag_tmp;
int len = 32;
/* get sign */
if( buf[0] == '1' ){
sign = -1;
} else {
sign = 1;
}
/* get exp */
for( exp=0, i=8, exp_tmp=1; i>0; i--){
if( buf[i] == '1') {
exp += exp_tmp;
}
exp_tmp*=2;
}
/* get fraction */
for(i=9, real=(double)0, frag_tmp = (double) 1/2; i< len; i++) {
if( buf[i] == '1') {
real += frag_tmp;
}
frag_tmp /= (double) 2;
}
while(exp>0) {
real *= 2;
exp--;
}
real *= (double) sign;
return real;
}
int ieee754_64(char *data, double real)
{
int exp=0, i=0, exp_tmp;
double cal, frag_tmp;
static char buf[64];
bzero(buf, sizeof(buf));
cal = real;
/* get sign */
if( cal < 0 ){
cal *= (double) -1;
buf[0] = 1;
} else {
buf[0] = 0;
}
/* get exp */
while( cal >= 1.0 ) {
cal /= 2;
exp++;
}
for( i=11, exp_tmp=1; i>0; i--){
if( (exp & exp_tmp) ) {
buf[i] = 1;
} else {
buf[i] = 0;
}
exp_tmp *=2 ;
}
/* get fraction */
for(i=12, frag_tmp = (double) 1/2; i< 64; i++) {
if( (cal - frag_tmp) >= 0 ){
buf[i] = 1;
cal = (double) cal - (double) frag_tmp;
} else {
buf[i] = 0;
}
frag_tmp /= (double) 2;
}
/* To ascii */
for(i=0; i<64; i++) {
buf[i] += '0';
}
strncpy(data, buf, 64);
return 0;
}
double rev_ieee754_64(char *buf)
{
int exp=0, i=0, exp_tmp, sign;
double real, frag_tmp;
int len=64;
/* get sign */
if( buf[0] == '1' ){
sign = -1;
} else {
sign = 1;
}
/* get exp */
for( exp=0, i=11, exp_tmp=1; i>0; i--){
if( buf[i] == '1') {
exp += exp_tmp;
}
exp_tmp*=2;
}
/* get fraction */
for(i=12, real=(double)0, frag_tmp = (double) 1/2; i< len; i++) {
if( buf[i] == '1') {
real += frag_tmp;
}
frag_tmp /= (double) 2;
}
while(exp>0) {
real *= 2;
exp--;
}
real *= (double) sign;
return real;
}
/* test */
int main(void)
{
int i, j;
char buf[32], buf2[64];
for(i=1; i<=1000000; i*=2) {
bzero(buf, sizeof(buf));
bzero(buf2, sizeof(buf2));
ieee754( (char*)buf, (double) i);
printf("[32bit] %20f ->\t", rev_ieee754( (char*)buf));;
for(j=0; j<sizeof(buf); j++) {
printf("%c ", buf[j]);
}
printf("\n");
ieee754_64( buf2, (double) i);
printf("[64bit] %20f ->\t", rev_ieee754_64( (char*)buf2));;
for(j=0; j<sizeof(buf2);j++) {
printf("%c ", buf2[j]);
}
printf("\n");
}
return 0;
}