On 09/05/2009 03:05 AM, Ed Boas wrote:
The following code:
----------
#include<stdio.h>
#include<inttypes.h>
// Rounds in current rounding mode, which is "round to closest
integer" by default on Pentium& Xeon
// Valid for |fval|<= 2^22 - 1, that is, -4194303<= fval<= 4914303
// based on code from www.lomont.org
inline int32_t fast_round(float x) {
x+=12582912; // 2^23+2^22
int32_t i=*(int32_t*)&x;
i&=8388607; // 2^23-1;
i-=4194304; // 2^22
return i;
}
int main(void) {
printf("%f rounds to %i\n", 1.4f, fast_round(1.4f));
return 0;
}
[...]
However, when it is compiled with g++ -O2, it prints:
1.400000 rounds to -4194304
[...]
Your code is not correct C++. Please read:
http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html
