CSAPP 第二章 homework(未完成)

void show_short(short s);
void show_long(long long l);
void show_double(double d);
void show_bytes(char *p, int size);

void show_short(short s) {
printf("the value of short %d is:", s);
show_bytes((char *)&s, sizeof(short));
}

void show_long(long long l) {
printf("the value of short %lld is:", l);
show_bytes((char *)&l, sizeof(long long));
}

void show_double(double d) {
printf("the value of short %lf is:", d);
show_bytes((char *)&d, sizeof(double));
}

/*
* 1 in little_endian
* *((char *)&i) means :
* 01 00 00 00 ----> 01
*/
int is_little_endian() {
int i = 1;
return *((char *)&i);
}

int graft(int x, int y) {
return (x & 0xff) | (y & ~0xff); //或也可以改成+
}

unsigned int graft2(unsigned int x,unsigned char y, int offset) {
return (x & ~(0xff << (offset << 3))) | (((unsigned int)y) << (offset << 3));
}

//A
return !~x;
//B
return !x;
//C
return !~((x >> ((sizeof(int) - 1) << 3));
//D
return !(x & 0xff);

return ~((~0)>>1);        //~0 = -1

int sra(int x, int k) {
//arithmetically
int xsrl = (unsigned) x >> k;
unsigned first_bit = x & (0x1 << (sizeof(int) * 8 - 1));
return xsrl + (((!first_bit) + ~0) << (sizeof(int) * 8 - k));
}

unsigned srl(unsigned x, int k) {
//logically
unsigned xsra = (int) x >> k;
unsigned first_bit = x & (0x1 << (sizeof(int) * 8 - 1));
return xsra & ~(~0 << (sizeof(int) * 8 - k));
}

int any_even_one(unsigned x) {
return !!(x & 0xaaaaaaaa);
}

int even_ones(unsigned x) {
x ^= (x >> 16);
x ^= (x >> 8);
x ^= (x >> 4);
x ^= (x >> 2);
x ^= (x >> 1);
return !(x & 0x1);
}

int leftmost_one(unsigned x) {
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return (x>>1) + 1;
}

int int_size_is_32(){
int set_msb = 1 << 31;
int beyond_msb = (1 << 16) << 16;
return set_msb && !beyond_msb;
}

int better_int_size_is_32() {
int seb_msb = ((1 << 8) << 8) << 15;
int beyond_msb = (((1 << 8) << 8) << 8) << 8;
return seb_msb && !beyond_msb;
}

//原题有点歧义，参数x没起到作用，于是把题目改成把x最低n位变成1
int lower_byte(int x, int n) {
return x | ((unsigned)(~0) >> (sizeof(int) * 8 - n));
}

unsigned rotate_right(unsigned x, int n) {
return (x >> n) + ((x << (sizeof(int) * 8 - n - 1)) << 1);
}

int fits_bits(int x, int n) {
x >>= (n - 1);
return !x || !(x + 1);
}