typedef unsigned char *byte_pointer;
void show_bytes(byte_pointer start, size_t len)
{size_t i ;for(i=0;i<len;i++){printf(" %.2x",start[i]);}printf("\n");
}
void show_int(int x)
{show_bytes((byte_pointer)&x,sizeof(int));
}

 int is_little_endian(byte_pointer start)
{if(start[0]==0xff) return 1;else return 0;
}
int main()
{size_t m =0xff;//byte_pointer start = (byte_pointer &m);if(is_little_endian((byte_pointer)&m)==1) printf("应是小端机");else printf("我猜是大端机");return 0;
}

   一张机，采桑陌上试春衣。风晴日暖慵无力， 桃花枝上，啼莺言语，不肯放人归。两张机，行人立马意迟迟。深心未忍轻分付， 回头一笑，花间归去，只恐被花知。三张机，吴蚕已老燕雏飞。东风宴罢长洲苑， 轻绡催趁，馆娃宫女，要换舞时衣。四张机，咿哑声里暗颦眉。回梭织朵垂莲子，盘花易绾，愁心难整，脉脉乱如丝。五张机，横纹织就沈郎诗。中心一句无人会， 不言愁恨，不言憔悴，只恁寄相思。六张机，行行都是耍花儿。花间更有双蝴蝶，停梭一晌，闲窗影里，独自看多时。七张机，鸳鸯织就又迟疑。只恐被人轻裁剪，分飞两处，一场离恨，何计再相随？八张机，回纹知是阿谁诗？织成一片凄凉意，行行读遍，恹恹无语，不忍更寻思。九张机，双花双叶又双枝。薄情自古多离别，从头到尾，将心萦系，穿过一条丝。

int main()
{size_t sign = 0xff; //size_t == unsigned intsize_t x = 0x89ABCDEF;size_t y = 0x76543210;size_t m = ((x&sign)|(y&~sign));show_int(m);return 0;
}

unsigned replace_byte (size_t x ,int i,unsigned char b)
{size_t k =x;size_t n =(unsigned)i<<3;size_t sign = 0xff<<n;size_t sb = (unsigned)b<<n;return (k & ~sign) | sb;}
int main()
{size_t x;size_t y;x = replace_byte(0x12345678,2,0xAB);y = replace_byte(0x12345678,0,0xAB);show_int(x);show_int(y);}

int any_odd_one(unsigned x)
{return !!(x & 0xAAAAAAAA);
}
int main()
{printf("%d",any_odd_one(0x5));return 0;
}

int lower_one_mask(int n)
{int w = sizeof(int)<<8;return (unsigned)-1>>(w-n); //注意这里的-1一定要是强制转为无符号
}
int main()
{show_int(lower_one_mask(6));show_int(lower_one_mask(17));
}

void copy(int val,void *buf,int maxbytes)
{if(maxbytes-(int)sizeof(val)>=0){memcpy(buf,(void *)&val,sizeof(val));printf("right\n");}else printf("Errrrrr\n");
}int main()
{int maxbytes = sizeof(int) * 10;void* buf = malloc(maxbytes);int val;val = 0x12345678;copy(val, buf, maxbytes);val = 0xAABBCCDD;copy(val, buf, 0);free(buf);return 0;
}

void *cccalloc(size_t nmemb,size_t size)
{if(nmemb==0||size==0) return NULL;size_t buf_size = nmemb * size;if (nmemb == buf_size / size) //判断是否溢出
    {void* ptr = malloc(buf_size);memset(ptr, 0, buf_size);return ptr;}return NULL;}
int main()
{void* p;p = cccalloc(0x1234, 1);if(p!=NULL)printf("rigjt!\n");free(p);p = cccalloc(SIZE_MAX, 2);//SIZE_MAX定义在头文件stdint.h中if(p == NULL)printf("ERRRR\n");free(p);return 0;
}

unsigned f2u(float x)
{return  *(unsigned*)&x;//&x取x的地址，(unsigned*)&x是把x的地址强制类型转换为unsigned,*(unsigned*)&x取转换后的值
}
int float_le(float x,float y)
{unsigned ux = f2u(x);unsigned uy = f2u(y);unsigned sx = ux >> 31;unsigned sy = uy >> 31;//浮点数的一个特点就是，如果大于0，则可以按unsigned位表示的大小排序。
//如果小于0则相反。注意都为0的情况即可。
//所以条件是：return ((ux<<1)==0 && (uy<<1)==0) ||(!sx && sy) ||(!sx && !sy && ux <= uy) ||(sx && sy && ux >= uy);}
int main()
{printf("%d",(float_le(+0, -0)));printf("%d",(float_le(2, 3)));
}

typedef unsigned float_bits;
float_bits float_negate(float_bits x)
{unsigned exp = (x>>23)&0xff;unsigned frac = x&0x7fffff;if((exp ==0xff)&&(frac!=0) ) return x;else return  x^0x80000000;
}

int float_f2i(float_bits x)
{unsigned sign =x>>31;unsigned exp = (x>>23)&0xff;unsigned frac = x&0x7fffff;unsigned bias = 0x7F;int int_x;unsigned E;unsigned M;if(exp>=0 &&(exp<bias))  int_x = 0; // x less than 1 ,than convert it to 0else if((exp-bias)>=31)  int_x = 0x80000000;else{E = exp - bias ;M = frac | 0x800000;if (E > 23) {int_x = M << (E - 23);} else {int_x= M >> (23 - E);}}return sign? -int_x:int_x;
}