IEEE754 浮点数转换

#include "stdafx.h"
#include <string.h>
#include <math.h>

float IEEE_754(int num);
#if 0
int main(int argc, char* argv[])
{
    float f;
    f = IEEE_754(0x00280000);
    printf("%f\r\n",f);
    f = IEEE_754(0x43BE1833); 
    printf("%f\r\n",f);
    f = IEEE_754(0x3FC00000); 
    printf("%f\r\n",f);
    f = IEEE_754(0x41D00000); 
    printf("%f\r\n",f);
    f = IEEE_754(0xBFC00000); 
    printf("%f\r\n",f);

    getchar();
    return 0;
}

//太小的数会当成0
float IEEE_754(int num)
{
    float f;
    int S,P,M;//符号位，指数，尾数
    S = num >> 31;
    P = (num & 0x7FFFFFFF) >> 23;
    M = (num & 0x007FFFFF);
    f = pow(2,-23);
    if(P == 0){
        f = pow(2,-126) * M*pow(2,-23);//*M;
    }else if(P != 0xFF){
        f = pow(2,P-127) * (1+M*pow(2,-23));//固定偏移127   
    }
    if(S){//符号位
        f = -f;
    }
    if(P==0 && M==0){
        f = 0;
    }
    return f;
}

#else


#include <iostream>
using namespace std;

int main(){
    unsigned int hex=0xBFC00000;//0x41360000;
    float* fp=(float*)&hex;//编译器内部浮点数使用的就是IEEE754标准
    cout<<"x="<<*fp<<endl;

    hex=0x00280000;
    fp=(float*)&hex;
    cout<<"x="<<*fp<<endl;
    hex=0x43BE1833;
    fp=(float*)&hex;
    cout<<"x="<<*fp<<endl;
    hex=0x3FC00000;
    fp=(float*)&hex;
    cout<<"x="<<*fp<<endl;
    hex=0x41D00000;
    fp=(float*)&hex;
    cout<<"x="<<*fp<<endl;
    hex=0xBFC00000;
    fp=(float*)&hex;
    cout<<"x="<<*fp<<endl;
    return 0;
}

#endif