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Date: Sat, 7 Dec 2019 15:38:04 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Patches for math subtree
On Sat, Dec 07, 2019 at 09:15:34PM +0100, Stefan Kanthak wrote:
> Just some optimisations.
>
> --- -/src/math/i386/remquo.s
> +++ +/src/math/i386/remquo.s
> @@ -23,23 +23,17 @@
> remquo:
> mov 20(%esp),%ecx
> fldl 12(%esp)
> fldl 4(%esp)
> mov 19(%esp),%dh
> xor 11(%esp),%dh
> 1: fprem1
> fnstsw %ax
> sahf
> jp 1b
> fstp %st(1)
> - mov %ah,%dl
> - shr %dl
> - and $1,%dl
> - mov %ah,%al
> - shr $5,%al
> - and $2,%al
> - or %al,%dl
> - mov %ah,%al
> - shl $2,%al
> - and $4,%al
> - or %al,%dl
> + setc %dl
> + shl $2,%ah
> + adc %dl,%dl
> + shl $5,%ah
> + adc %dl,%dl
> test %dh,%dh
>
> --- -/src/math/ceil.c
> +++ +/src/math/ceil.c
> @@ -18,10 +18,10 @@
> + /* special case because of non-nearest rounding modes */
> + if (e < 0x3ff) {
> + FORCE_EVAL(y);
> + return u.i >> 63 ? -0.0 : 1.0;
> + }
> /* y = int(x) - x, where int(x) is an integer neighbor of x */
> if (u.i >> 63)
> y = x - toint + toint - x;
> else
> y = x + toint - toint - x;
> - /* special case because of non-nearest rounding modes */
> - if (e <= 0x3ff-1) {
> - FORCE_EVAL(y);
> - return u.i >> 63 ? -0.0 : 1;
> - }
>
> --- -/src/math/floor.c
> +++ +/src/math/floor.c
> @@ -18,10 +18,10 @@
> + /* special case because of non-nearest rounding modes */
> + if (e < 0x3ff) {
> + FORCE_EVAL(y);
> + return u.i >> 63 ? -1.0 : 0.0;
> + }
> /* y = int(x) - x, where int(x) is an integer neighbor of x */
> if (u.i >> 63)
> y = x - toint + toint - x;
> else
> y = x + toint - toint - x;
> - /* special case because of non-nearest rounding modes */
> - if (e <= 0x3ff-1) {
> - FORCE_EVAL(y);
> - return u.i >> 63 ? -1 : 0;
> - }
Do you have any explanation of why these are optimizations?
Rich
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