csapp-Lecture1-4

#include "stdio.h"
#include "stdlib.h"

int main(){
    //写入一个整数16
    //32位的int表示为：00000000 00000000 00000000 00010000
    //用unsigned char去模拟
    unsigned char *uc=(unsigned char*)malloc(sizeof(unsigned char)*4); 
    uc[0]=0b00010000;
    uc[1]=0b00000000;
    uc[2]=0b00000000;
    uc[3]=0b00000000;
    printf("%d\n",*((int*)uc));
    //写入一个double
    //32位的float表示 (-1)**S*1.M*2**E
    // 正数 S=0 M=0 E=1 这个数字为2 
    //32 float IEEE编码为 01000000 00000000 00000000 00000000
    uc[0]=0b00000000;
    uc[1]=0b00000000;
    uc[2]=0b00000000;
    uc[3]=0b01000000;
    printf("%f\n",*((float*)uc));
    //float表示正无穷， 01111111 10000000 00000000 00000000
    uc[0]=0b00000000;
    uc[1]=0b00000000;
    uc[2]=0b10000000;
    uc[3]=0b01111111;
    printf("%f\n",*((float*)uc));
    //float表示NAN 01111111 11111111 00000000 00000000
    uc[0]=0b00000000;
    uc[1]=0b00000000;
    uc[2]=0b11111111;
    uc[3]=0b01111111;
    printf("%f",*((float*)uc));
    //浮点数不具有结合律，表现在当一个很大的数去加减一个很小的数的时候
    print("%f\n",(3.14+1e10)-1e100);
    print("%f\n",3.14+(1e10-1e100));
    return 0;
}