On Wed, Aug 13, 2003 at 09:40:29 -0400, Pete Yadlowsky wrote: > Yes. I believe double-precision is the standard data type used by most > floating-pt processors. Single-precision floats must first be converted to > doubles at each computation, thus actually degrading performance slightly.
This is actually not generally true. In the 387 they are all converted to long doubles (80 or 96 bit, I forget which) and processing in SSE (and 3DNow and Altivec IIRC) is nativly 4x32 bits wide. SSE2 is nativly 4x64 bits. You are correct that there is no /processor/ overhead to double v's floats (in 387, its not true in all systems) the difference comes from memory and cache effects - most DSP routines are memory bandwidth starved - its actually quite hard to fill the FPU pipelines. - Steve
