From a4a0c91275788407763b1e5a9da17b777495ca85 Mon Sep 17 00:00:00 2001 From: nsz Date: Thu, 22 Mar 2012 14:54:47 +0100 Subject: [PATCH] acos.s fix: use the formula acos(x) = atan2(sqrt(1-x),sqrt(1+x)) the old formula atan2(1,sqrt((1+x)/(1-x))) was faster but could give nan result at x=1 when the rounding mode is FE_DOWNWARD (so 1-1 == -0 and 2/-0 == -inf), the new formula gives -0 at x=+-1 with downward rounding. --- src/math/i386/acos.s | 4 +--- src/math/x86_64/acosl.s | 4 +--- 2 files changed, 2 insertions(+), 6 deletions(-) diff --git a/src/math/i386/acos.s b/src/math/i386/acos.s index 4f0168f6..bfff0c5c 100644 --- a/src/math/i386/acos.s +++ b/src/math/i386/acos.s @@ -18,12 +18,10 @@ acos: fld %st(1) fld1 fsubp + fsqrt fxch %st(2) faddp - fdivp fsqrt - fld1 - fxch %st(1) fpatan fld1 fld1 diff --git a/src/math/x86_64/acosl.s b/src/math/x86_64/acosl.s index 92c29870..db68d2de 100644 --- a/src/math/x86_64/acosl.s +++ b/src/math/x86_64/acosl.s @@ -6,12 +6,10 @@ acosl: fld %st(1) fld1 fsubp + fsqrt fxch %st(2) faddp - fdivp fsqrt - fld1 - fxch %st(1) fpatan fld1 fld1 -- 2.25.1