2.61 判断指定字节数据

//csapp2.61 编写表达式，下列条件下产生1，否则0,假设x是int类型，不允许使用 ==，!=

#include <stdio.h>                                                                                                                                                                 
typedef unsigned char* byte_printer;
//打印二进制数据
void show_bytes (byte_printer start, size_t len)
{
    size_t i;
    for (i=0; i<len; i++) 
    {
        printf("%.2x", *(start+i));
    }
    printf("\r\n");
}
//所有bit位都等于1
int all_bit_is_one(int x)
{
    return !(~x);
}
//所有bit都等于0
int all_bit_is_zero(int x)
{
    return !x;
}
//最低有效字节所有位都等于1  
int little_byte_is_one(int x)
{
    /*
     * 方法一：掩码
        int mask = ~0xFF;
        all_bit_is_ont(x|mask);
     */
    //方法二：位运算
    unsigned int w = sizeof(int)<<3;
    return all_bit_is_one(x<<(w-8)>>(w-8));
}
//最高有效字节，所有位都等于0 
int top_byte_is_zero(int x)
{
    unsigned int w = sizeof(int)<<3;
    return !(x>>(w-8));
}   
    
int main(void)
{   
    printf("all_bit_is_one : expect:1,result:%d\r\n", all_bit_is_one(-1));
    printf("all_bit_is_one : expect:0,result:%d\r\n", all_bit_is_one(-2));
    printf("all_bit_is_one : expect:0,result:%d\r\n", all_bit_is_one(0));
    printf("all_bit_is_one : expect:0,result:%d\r\n", all_bit_is_one(1));
    printf("all_bit_is_one : expect:0,result:%d\r\n", all_bit_is_one(2));
    
    printf("all_bit_is_zero : expect:1,result:%d\r\n", all_bit_is_zero(0));
    printf("all_bit_is_zero : expect:0,result:%d\r\n", all_bit_is_zero(-1));
    printf("all_bit_is_zero : expect:0,result:%d\r\n", all_bit_is_zero(-2));
    printf("all_bit_is_zero : expect:0,result:%d\r\n", all_bit_is_zero(1));
    printf("all_bit_is_zero : expect:0,result:%d\r\n", all_bit_is_zero(2));

    printf("little_byte_is_one(-1) : expect:1,result:%d\r\n", little_byte_is_one(-1));
    printf("little_byte_is_one(0xFF) : expect:1,result:%d\r\n", little_byte_is_one(0xFF));
    printf("little_byte_is_one(-2) : expect:0,result:%d\r\n", little_byte_is_one(-2));
    printf("little_byte_is_one(1) : expect:0,result:%d\r\n", little_byte_is_one(1));
    printf("little_byte_is_one(2) : expect:0,result:%d\r\n", little_byte_is_one(2));

    printf("top_byte_is_zero(0) : expect:1,result:%d\r\n", top_byte_is_zero(0));
    printf("top_byte_is_zero(1<<(w-8)) : expect:0,result:%d\r\n", top_byte_is_zero(1<<(w-8)));

    return 1;
}

2.61 判断指定字节数据

原文：https://www.cnblogs.com/LonelyTraveler/p/12864649.html