我想在1和动态值bit_cnt之间创建一个rand（）范围。
在阅读了关于rand（）函数的更多信息后，我明白开箱即用的rand（）的范围是[0，RAND_MAX]。我也理解RAND_MAX的值与库有关，但保证至少为32767.
我必须创建一个64 0的位掩码。
现在，我试图将位掩码移动动态值为bit_cnt，并且随机生成的位数在1和动态值bit_cnt之间。
例如，当bit_cnt为10时，我想将最低10位随机化。
最初，我有
mask = (mask << bit_cnt) + (rand()% bit_cnt);
导致浮点异常。根据我的理解，发生了异常，因为bit_cnt的值变为0。
因此，我试图创建一个这样的if语句：
if((rand()%bit_cnt))!=0){
mask = (mask << bit_cnt) + (rand()% bit_cnt);
}
，但仍然发生了浮点异常。
然后我尝试了以下认为值不是0因此将值增加到至少1：
mask = (mask << bit_cnt) + ((rand()% bit_cnt)+1);
，但仍然发生了浮点异常。
之后，我尝试了以下内容：
mask = (mask << bit_cnt) + (1+(rand()%(bit_cnt+1)));
以及随后的20行64位输出：
0000000000000000000000000000000000000000000000000000000000000010
0000000000000000000000000000000000000000000000000000000000000011
0000000000000000000000000000000000000000000000000000000000000101
0000000000000000000000000000000000000000000000000000000000001010
0000000000000000000000000000000000000000000000000000000000010011
0000000000000000000000000000000000000000000000000000000000100011
0000000000000000000000000000000000000000000000000000000001000110
0000000000000000000000000000000000000000000000000000000010000100
0000000000000000000000000000000000000000000000000000000100001001
0000000000000000000000000000000000000000000000000000001000000010
0000000000000000000000000000000000000000000000000000010000000100
0000000000000000000000000000000000000000000000000000100000000111
0000000000000000000000000000000000000000000000000001000000000101
0000000000000000000000000000000000000000000000000010000000001001
0000000000000000000000000000000000000000000000000100000000000111
0000000000000000000000000000000000000000000000001000000000001111
0000000000000000000000000000000000000000000000010000000000001010
0000000000000000000000000000000000000000000000100000000000000101
0000000000000000000000000000000000000000000001000000000000001101
0000000000000000000000000000000000000000000010000000000000001100
浮点异常的原因是什么？这是如何动态创建一个范围的rand（）函数？
我感谢任何建议。谢谢。
更新： 我将if语句改为：
if(bit_cnt !=0)
然后执行剩下的逻辑。
我收到了以下输出：
0000000000000000000000000000000000000000000000000000000000000001
0000000000000000000000000000000000000000000000000000000000000010
0000000000000000000000000000000000000000000000000000000000000100
0000000000000000000000000000000000000000000000000000000000001000
0000000000000000000000000000000000000000000000000000000000010010
0000000000000000000000000000000000000000000000000000000000100001
0000000000000000000000000000000000000000000000000000000001000100
0000000000000000000000000000000000000000000000000000000010000110
0000000000000000000000000000000000000000000000000000000100000011
0000000000000000000000000000000000000000000000000000001000000000
0000000000000000000000000000000000000000000000000000010000001000
0000000000000000000000000000000000000000000000000000100000000111
0000000000000000000000000000000000000000000000000001000000000110
0000000000000000000000000000000000000000000000000010000000000110
0000000000000000000000000000000000000000000000000100000000001100
0000000000000000000000000000000000000000000000001000000000000010
0000000000000000000000000000000000000000000000010000000000001101
0000000000000000000000000000000000000000000000100000000000000110
0000000000000000000000000000000000000000000001000000000000010000
0000000000000000000000000000000000000000000010000000000000000100
有没有办法知道范围是否正确？就像通过查看输出有什么可能的方法来知道吗？
const int LINE_CNT = 20;
void print_bin(uint64_t num, unsigned int bit_cnt);
uint64_t rand_bits(unsigned int bit_cnt);
int main(int argc, char *argv[]) {
int i;
srand(time(NULL));
for(i = 0; i < LINE_CNT; i++) {
uint64_t val64 = rand_bits(i);
print_bin(val64, 64);
}
return EXIT_SUCCESS;
}
void print_bin(uint64_t num, unsigned int bit_cnt) {
int top_bit_cnt;
if(bit_cnt <= 0) return;
if(bit_cnt > 64) bit_cnt = 64;
top_bit_cnt = 64;
while(top_bit_cnt > bit_cnt) {
top_bit_cnt--;
printf(" ");
}
while(bit_cnt > 0) {
bit_cnt--;
printf("%d", (num & ((uint64_t)1 << bit_cnt)) != 0);
}
printf("\n");
return;
}
uint64_t rand_bits(unsigned int bit_cnt) {
uintmax_t mask = 1;
if (bit_cnt != 0) {
mask = (mask << bit_cnt) + (rand()% bit_cnt);
}
return mask;
}
我正在尝试修改函数rand_bits以返回所有随机化的最低位bit_cnt的0期望值。
返回一个64位模式，除了最低请求位以外，所有零都是零。这允许以便携方式任意长度的随机位模式作为C标准＆＃34; rand（）＆＃34;功能只需返回
0到32767之间的随机数...有效地，随机15位模式。
参数，＆＃34; bit_cnt＆＃34;：有多少最低位，包括要随机化的最低位（位0）。
更新：添加了Barmar对mask = rand() % (1 << bit_cnt);的最新建议：
0000000000000000000000000000000000000000000000000000000000000001
0000000000000000000000000000000000000000000000000000000000000001
0000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000010
0000000000000000000000000000000000000000000000000000000000001000
0000000000000000000000000000000000000000000000000000000000001001
0000000000000000000000000000000000000000000000000000000000000010
0000000000000000000000000000000000000000000000000000000000010101
0000000000000000000000000000000000000000000000000000000001001111
0000000000000000000000000000000000000000000000000000000010000011
0000000000000000000000000000000000000000000000000000001010101001
0000000000000000000000000000000000000000000000000000010101101100
0000000000000000000000000000000000000000000000000000101011111000
0000000000000000000000000000000000000000000000000001001010101111
0000000000000000000000000000000000000000000000000011101011000101
0000000000000000000000000000000000000000000000000001001101111101
0000000000000000000000000000000000000000000000001111000000111010
0000000000000000000000000000000000000000000000000101100000001100
0000000000000000000000000000000000000000000000100111101000111111
0000000000000000000000000000000000000000000001010101011101000110
uint64_t rand_bits(unsigned int bit_cnt) {
uintmax_t mask = 1;
if (bit_cnt != 0) {
mask = rand() % (1 << bit_cnt);
}
return mask;
}
答案 0 :(得分：2)
问题是如果anything % bit_cnt为bit_cnt，则0会出错。您需要先检查bit_cnt ，然后尝试执行模数。
if (bit_cnt != 0) {
mask = (mask << bit_cnt) + (rand()% bit_cnt) + 1;
}
你所有的尝试都执行了模数然后尝试对结果做了一些事情，但是在错误发生后就是这样。
答案 1 :(得分：0)
这使用位计数来生成掩码。如果你想要比WHERE更大的位数，请实现我之前评论过的另一个随机函数。
RAND_MAX节目输出：
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void) {
int bit_cnt = 10;
unsigned mask = 0;
int i;
int num;
srand((unsigned)time(NULL));
for(i = 0; i < bit_cnt; i++)
mask = (mask << 1) | 1;
printf ("For bit_cnt=%d, mask=0x%X\n\n", bit_cnt, mask);
for (i = 0; i < 5; i++) {
num = rand() & mask;
printf("Random number 0x%0*X\n", 1+(bit_cnt-1)/4, num);
}
}