On Fri, Jun 13, 2003 at 03:42:26PM -0700, John R Pierce wrote: > The extended FP multiply has 64 bits of mantissa. SSE2 is, I believe, > restricted to 32bit multiplies, so it would take 4 times as many to equal > one 64bit (gross simplification, but sufficient for the purposes here).
SSE2 can handle 64 bit floating point numbers (not that I can remember off the top of my head how many bits of mantissa there are in those) -- the traditional x86 FPU can handle 80 bits internally, but usually you only save 64 bits of those. In other words, precision is not _that_ big of an issue, even though Prime95 has more conservative limits for SSE2 CPUs. (SSE1, on the other hand, only supports 32 bit numbers, and thus is not usable for Prime95.) The biggest problem with SSE2 is of course that it's only supported on the Pentium 4 yet -- they are becoming increasingly common, but for instance, no current AMD chip supports it. /* Steinar */ -- Homepage: http://www.sesse.net/ _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
