X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fmath%2Fi386%2Facos.s;h=47f365efb1ea7493c34f7d64b7db33761e4337bd;hb=f4ded939bf90cd6baed6b4e723e54a62c9bdb6b9;hp=6f9ef7f0e37ada36bc53e9b37a3c1d234f528be6;hpb=bc33e617040166e971ec1e6822ac1cc417eb6c9c;p=musl

diff --git a/src/math/i386/acos.s b/src/math/i386/acos.s
index 6f9ef7f0..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:
@@ -15,10 +17,12 @@ acosl:
 acos:
 	fldl 4(%esp)
 1:	fld %st(0)
-	fmul %st(0)
 	fld1
-	fsubp %st(1)
+	fsub %st(0),%st(1)
+	fadd %st(2)
+	fmulp
 	fsqrt
+	fabs         # fix sign of zero (matters in downward rounding mode)
 	fxch %st(1)
 	fpatan
 	ret