[LLVMdev] [RFC] Add a simple soft-float class

[Owen Anderson]

On Jun 18, 2014, at 9:30 AM, Sean Silva <chisophugis at gmail.com> wrote:

> On Tue, Jun 17, 2014 at 10:11 PM, Rafael Avila de Espindola <rafael.espindola at gmail.com> wrote:
> If we require the host to have sse2 or other IEEE 754 conformant  implementation, would it be possible to use hardware float?
> 
> I don't think that IEEE 754 actually guarantees bit-exact results in all cases.


IEEE 754 accuracy guarantees are expressed in terms of ULPs: Units-in-the-Last-Place.  Most of the primitive operations are accurate to +/- 0.5 ULPs, which is equivalent to saying that there is a single bit-accurate result (for a given rounding mode).  Once you get into transcendentals, you start getting operations with much wider ULP bounds.

—Owen
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