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-rw-r--r--sysdeps/i386/fpu/e_acos.S10
1 files changed, 6 insertions, 4 deletions
diff --git a/sysdeps/i386/fpu/e_acos.S b/sysdeps/i386/fpu/e_acos.S
index d10a054b9c..586c7fc406 100644
--- a/sysdeps/i386/fpu/e_acos.S
+++ b/sysdeps/i386/fpu/e_acos.S
@@ -7,13 +7,15 @@
 
 RCSID("$NetBSD: e_acos.S,v 1.4 1995/05/08 23:44:37 jtc Exp $")
 
-/* acos = atan (sqrt(1 - x^2) / x) */
+/* acos = atan (sqrt((1-x) (1+x)) / x) */
 ENTRY(__ieee754_acos)
 	fldl	4(%esp)			/* x */
 	fld	%st			/* x : x */
-	fmul	%st(0)			/* x^2 : x */
-	fld1				/* 1 : x^2 : x */
-	fsubp				/* 1 - x^2 : x */
+	fld1				/* 1 : x : x */
+	fsubp				/* 1 - x : x */
+	fld1				/* 1 : 1 - x : x */
+	fadd	%st(2)			/* 1 + x : 1 - x : x */
+	fmulp				/* 1 - x^2 : x */
 	fsqrt				/* sqrt (1 - x^2) : x */
 	fabs
 	fxch	%st(1)			/* x : sqrt (1 - x^2) */