Question

以下代码将L位从LSB的N个起始位置P设置为X位（N为32位数字）

//gcc 5.4.0
#include  <stdio.h>
unsigned int set_bits_pos(int N, int X, int P)
{
    unsigned int mask = ((1UL << X)-1) << P; 
    return (N|mask);
}

int main(void)
{
    unsigned int bits = 3, pos=5, num=0x0F;       
    printf("0x%X\n", set_bits_pos(num,bits,pos));
    return 0;
}

输出：

0xEF

如何转换上述功能，以将N位的X位设置为MSB的起始位置P？最好的方法。谢谢

编辑：建议后，可从MSB和独立于Arch的32和64位N进行设置

//gcc 5.4.0
#include  <stdio.h>
size_t set_bits_pos(size_t N, int X, int P)
{
    size_t mask = ((1UL << X)-1) << ((8*sizeof(N)) - P - X); 
    return (N|mask);
}

int main(void)
{
    size_t num=0x0F;
    int bits = 3, pos=5;       
    printf("0x%X\n", set_bits_pos(num,bits,pos));
    return 0;
}

输出：

0x0700000F

Answer 1

我建议使用精确宽度整数类型：

list = ['f','g','p','a','p','c','b','q','z','n','d','t','q'];
noOfPs = [i for i in l if i == 'p']; 
noOfQs = [i for i in l if i == 'q'];
resultList= noOfPs + sorted(filter(lambda x:x not in {'q', 'p'}, l))+ noOfQs

#include <inttypes.h> uint32_t set_low32(const uint32_t value, const unsigned int bits, const unsigned int skip) { uint32_t mask = (~(uint32_t)0) >> (32 - bits); return value | (mask << skip); } uint64_t set_low64(const uint64_t value, const unsigned int bits, const unsigned int skip) { uint64_t mask = (~(uint64_t)0) >> (64 - bits); return value | (mask << skip); } uint32_t set_high32(const uint32_t value, const unsigned int bits, const unsigned int skip) { uint32_t mask = (~(uint32_t)0) << (32 - bits); return value | (mask >> skip); } uint64_t set_high64(const uint64_t value, const unsigned int bits, const unsigned int skip) { uint64_t mask = (~(uint64_t)0) << (64 - bits); return value | (mask >> skip); }是要设置的位数（有问题的bits，而X是要跳过的低/高位数（有问题的skip）

从MSB的位置P开始，有效地将X位设置为N个数字

1 个答案: