Re: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86

[N8TM at aol dot com]

In a message dated 12/16/98 12:36:17 PM Pacific Standard Time, pcg@goof.com
writes:

<< I still don't see what the 64 bit precision idea gives us, in terms of
 performance. First, it doesn't give us full ieee, second, it kills
 performance, depending on where the rounding mode is set (before each
 assignment? resetting it to normal before each long double assignment?)
 
 IAW, how is 64 bit rounding mode going to be faster? For me, it seems this
 creates a similar situation to the float->integer conversion, i.e. save and
 restoring the control word with each assignment. >>
Although I haven't seen anyone specify this, I assume they mean to leave
64-bit mode set throughout the program, or at least for the duration of any
intensive computing.  I've tried running Livermore Fortran Kernels this way,
and it does speed up division and sqrt(), as it should.  It works reasonably
well as long as all arithmetic is intended to be ordinary single or double
precision.