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标题:
关于在SCO OpenServer 5.0.7(mp5)VMware 5.5.1 build-19175 环境下数值计算的怪现象
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作者:
mayoryang
时间:
2006-10-06 20:13
标题:
关于在SCO OpenServer 5.0.7(mp5)VMware 5.5.1 build-19175 环境下数值计算的怪现象
源代码:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
typedef struct
{
unsigned h32bit; /*Valid values are from 0to 4294967295*/
int l32bit; /*Valid values are from -2147483648 to 2147483647*/
}
__int64; /*Valid values are from -9223372036854775808 to 9223372036854775807*/
int main(void)
{
double d_int64 = 0.00;
double d_int64_h32bit = 0.00;
double d_int64_l32bit = 0.00;
__int64 st_int64;
memset((__int64 *)&st_int64, 0x00, sizeof(st_int64));
st_int64.h32bit = 4294967295;
st_int64.l32bit = 2147483647;
d_int64_h32bit = (double)st_int64.h32bit + 1;
d_int64_l32bit = (double)st_int64.l32bit + 1;
d_int64 = d_int64_h32bit * d_int64_l32bit;
printf(\"h32bit[%.lf]\\n\", d_int64_h32bit);
printf(\"l32bit[%.lf]\\n\", d_int64_l32bit);
printf(\"__int64[%.lf]\\n\", d_int64);
exit(0);
}
编译命令:
cc -O int64.c -s -o int64 -lm
输出结果:
h32bit[4294967296]
l32bit[2147483648]
__int64[9223372036854775810]
困惑之处:
最后一行输出的正确答案应该是:9223372036854775808,为何计算结果多2?
作者:
xxyyy
时间:
2006-10-06 22:06
呵呵,楼主为何用double来计算整数?请注意,double的精确度(有效数字长度为18),9223372036854775808有效数字位数为19
[
本帖最后由 xxyyy 于 2006-10-6 22:08 编辑
]
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