H. J. Lu wrote: > Have you added -march=pentium4 to -mfpmath? YES, as stated in the *original post*. The EXACT base command line is: gcc -std=gnu99 -lm -lrt -O3 -ffast-math -march=pentium4 or gcc -std=gnu99 -lm -lrt -O3 -ffast-math -march=pentium4 -mfpmath=sse ..Scott