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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