csapp2e 家庭作业 2.94

#include <stdio.h>
 
typedef unsigned float_bits;
 
float_bits float_twice(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 += frac << 1 >>23;
   frac = (frac<<1);
  }
  else if(exp != 0xff)
   ++exp;
  if(exp == 0xff)
   frac = 0;
  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*2.0;
   ur = float_twice(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;
   }
 
 }
 }