ch02 课下作业
2.96
代码
#include <stdio.h>
#include <stdlib.h>
typedef unsigned float_bits;
float u2f(unsigned x){
return *((float*)&x);
}
int float_f2i(float_bits f){
unsigned sign = f>>31;
int exp = (f>>23) & 0xFF;
int frac = (f&0x7FFFFF) | (1<<23);
exp -= 127;
if(exp < 0) return 0;
if(exp >= 31) return 0x80000000; //绝对值不大于2^31（1<<31）
if(exp > 23) frac <<= (exp - 23);
else frac >>= (23 - exp);
return sign? -frac : frac;
}
void main(){
int x = 0;
do{
int m = float_f2i(x);
int n = (int)u2f(x);
if(m != n){
printf("error in %x: %d %d
", x, m, n);
return;
}
x++;
}while(x!=0);
printf("Test OK
");
}
- 利用循环做测试，但这个循环耗时很久
测试结果：
2.97
代码
#include <stdio.h>
#include <stdlib.h>
typedef unsigned float_bits;
unsigned f2u(float f){
return *((unsigned*)&f);
}
int is_float_equal(float_bits f1, float f2){
return f2u(f2) == f1;
}
float_bits float_i2f(int i)
{
if(i == 0) return 0;
unsigned x = i>0?i:-i;
int sign = i>0?0:1;
int w = sizeof(int)<<3;
int j;
for(j=w-1; j>=0; j--){ //找到最高位
if( (x>>j) & 1) break;
}
unsigned bias = 127;
unsigned exp, frac;
exp = bias + j;
if(j <= 23) frac = x<<(23-j);
else {
frac = x>>(j-23);
unsigned mask = (1<<(j-23)) - 1;
if( (x&mask) > (1<<(j-24)) ) frac++; //需要舍入 到大值
else if( (x&mask) == 1<<(j-24) && (frac&1)) frac++; //舍入到偶数
if(frac == (1<<24)) exp++; //舍入到偶数超过 (1<<24) - 1，指数需要再加1
}
return sign<<31 | exp<<23 | frac&0x7FFFFF;
}
void main(){
int x = 0;
do{
float_bits fb = float_i2f(x);
float ff = (float)x;
if(!is_float_equal(fb, ff)){
printf("error in %d: %x %x
", x, fb, f2u (ff));
return;
}
x++;
}while(x!=0);
printf("Test OK
");
}
测试结果：
