optimization bug in g++ 4.3.3

[Ed Boas]

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;
}
----------

produces the correct output when compiled using g++ -O:

1.400000 rounds to 1

However, when it is compiled with g++ -O2, it prints:

1.400000 rounds to -4194304

I don't know anything about assembly, so I can't diagnose the reason
for this problem.  I am using g++ Ubuntu 4.3.3 on AMD Opteron.  Any
ideas?

Thanks!
Ed

________________________________
F. Edward Boas
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650-787-1688
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