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-rw-r--r--src/math/i386/acos.s18
1 files changed, 8 insertions, 10 deletions
diff --git a/src/math/i386/acos.s b/src/math/i386/acos.s
index bfff0c5c..47f365ef 100644
--- a/src/math/i386/acos.s
+++ b/src/math/i386/acos.s
@@ -1,3 +1,5 @@
+# use acos(x) = atan2(fabs(sqrt((1-x)*(1+x))), x)
+
.global acosf
.type acosf,@function
acosf:
@@ -14,17 +16,13 @@ acosl:
.type acos,@function
acos:
fldl 4(%esp)
-1: fld1
- fld %st(1)
+1: fld %st(0)
fld1
- fsubp
- fsqrt
- fxch %st(2)
- faddp
+ fsub %st(0),%st(1)
+ fadd %st(2)
+ fmulp
fsqrt
+ fabs # fix sign of zero (matters in downward rounding mode)
+ fxch %st(1)
fpatan
- fld1
- fld1
- faddp
- fmulp
ret