use alternate formula for acos asm to avoid loss of precision

[musl] / src / math / i386 / acos.s

diff --git a/src/math/i386/acos.s b/src/math/i386/acos.s
index 6f9ef7f..4f0168f 100644 (file)
--- a/src/math/i386/acos.s
+++ b/src/math/i386/acos.s
@@ -14,11 +14,19 @@ acosl:
 .type acos,@function
 acos:
        fldl 4(%esp)
-1:     fld %st(0)
-       fmul %st(0)
+1:     fld1
+       fld %st(1)
        fld1
-       fsubp %st(1)
+       fsubp
+       fxch %st(2)
+       faddp
+       fdivp
        fsqrt
+       fld1
        fxch %st(1)
        fpatan
+       fld1
+       fld1
+       faddp
+       fmulp
        ret