14 Aug
2003
14 Aug
'03
7 a.m.
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