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Re: FWD: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86
- To: burley at gnu dot org, egcs at egcs dot cygnus dot com
- Subject: Re: FWD: FLOATING-POINT CONSISTENCY, -FFLOAT-STORE, AND X86
- From: Brad Lucier <lucier at math dot purdue dot edu>
- Date: Thu, 17 Dec 1998 14:27:02 -0500 (EST)
- Cc: lucier at math dot purdue dot edu
I agree with Craig (I think ;-).
To get consistent, predictable, useable floating-point results, it is
absolutely necessary that spilled floating-point registers be stored in
memory in a format such that spilling and reading a value back into a
register does not change one bit (in the technical sense) of the number.
If that means spilling FP registers to 80 bit temporaries aligned to
128-bit (or 64bit) boundaries, then so be it.
I say this as someone who has built highly accurate elementary function
routine libraries, together with test libraries for those routines, built
test libraries for last-bit accuracy floating-point IO routines, etc.
The programmer needs absolute control over the precision and range of
all results, including intermediate results, for him/her to be successful
at things like this.
Brad Lucier lucier@math.purdue.edu