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authornsz <nsz@port70.net>2012-03-22 14:54:47 +0100
committernsz <nsz@port70.net>2012-03-22 14:54:47 +0100
commita4a0c91275788407763b1e5a9da17b777495ca85 (patch)
tree1c4e53cfe0c6b0ab80df621813acb74715e9ab3b /src/math/i386
parent2e0c1fed36be1f1435de79bfc7cdc34824cb5614 (diff)
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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.
Diffstat (limited to 'src/math/i386')
-rw-r--r--src/math/i386/acos.s4
1 files changed, 1 insertions, 3 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