csapp2e 家庭作业 2.93

#include <stdio.h>

typedef unsigned float_bits;

float_bits float_half(float_bits f)
{
	unsigned sign = f>>31;
	unsigned exp = f>>23&0xff;
	unsigned frac = f&0x7fffff;

	if(exp == 0xff)
		return f;
	if(exp > 0)
	{
		--exp;
		if(exp == 0)
			frac+=1<<23;
	}
	if(exp ==0)
	{
		if((frac&0x3)==0x3)
			frac=(frac>>1)+1;
		else
			frac>>=1;

	}
	
	return (sign<<31)|(exp<<23)|frac;
}

int main()
{
	
	unsigned u,ur;
	float f,fr;

	for(u=0;u<=0xffffffffu;u++)
	{
		f =*((float *)&u);
		f=f*0.5;
		ur = float_half(u);
		fr = *((float *)&ur);
		if(fr == f)
			printf("%u: %x %x ok\n",u,f,fr);
		else
		{
			printf("%u: error\n",u);
			printf("%x %x\n",f,fr);
			return -1;
		}

	}
}