Do I have a gcc optimization bug or a C code problem?
c, gcc
Solution
Use the compiler flag -fno-strict-aliasing.
With strict aliasing enabled, as it is by default for at least -O3, in the line:
size_t t = *((size_t*)&f);
the compiler assumes that the size_t* does NOT point to the same memory area as the float*. As far as I know, this is standards-compliant behaviour (adherence with strict aliasing rules in the ANSI standard start around gcc-4, as Thomas Kammeyer pointed out).
If I recall correctly, you can use an intermediate cast to char* to get around this. (compiler assumes char* can alias anything)
In other words, try this (can't test it myself right now but I think it will work):
size_t t = *((size_t*)(char*)&f);
Problem
Test the following code: ``` #include <stdio.h> #include <stdlib.h> main() { const char *yytext="0"; const float f=(float)atof(yytext); size_t t = *((size_t*)&f); printf("t should be 0 but is %d\n", t); } ``` Compile it with: ``` gcc -O3 test.c ``` The GOOD output should be: ``` "t should be 0 but is 0" ``` But with my gcc 4.1.3, I have: ``` "t should be 0 but is -1209357172" ```