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Date: Thu, 16 Jan 2020 15:30:03 +1100 (AEDT)
From: Damian McGuckin <damianm@....com.au>
To: musl@...ts.openwall.com
Subject: Considering x86-64 fenv.s to C
I was just looking at fenv.s in x86-64 with a view to doing this as C-code
with some __asm__. I have limited experience with playing with this stuff
in an SSE-only environment, i.e. no 80-bit floats. Before I attempt
anything, I need to expand my knowledge.
My observations on
musl-1.1.24/src/fenv/x86_64/fenv.s
* feclearexcept
considers both the X87 status word and the SSE MXCSR
* feraiseexcept
ignores the X87 status word and considers only the SSE MXCSR
* fetesteexcept
considers both the X87 status word and the SSE MXCSR
* fesetround
considers both the X87 control word and the SSE MXCSR
* fegetround
ignores the X87 control word and considers only the SSE MXCSR
Why is the X87 component of the FPU control/status sometimes ignored and
sometimes not?
Does the X87 control or status bits automatically flow through to the
equivalent stuff in the SSE or vica-versa?
I assume that 'fwait' is irrelevant and unnecessary, even if one is using
the x87 FPU?
Regards - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer
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