From 728d7b43fc8a4f9b3ec772fd8b75a39b945e9f04 Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Thu, 17 Jan 2013 20:25:51 +0000
Subject: Fix cacos real-part inaccuracy for result real part near 0 (bug
 15023).

---
 math/s_cacos.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

(limited to 'math/s_cacos.c')

diff --git a/math/s_cacos.c b/math/s_cacos.c
index 6604b5aec6..acd9b2462a 100644
--- a/math/s_cacos.c
+++ b/math/s_cacos.c
@@ -25,11 +25,27 @@ __cacos (__complex__ double x)
 {
   __complex__ double y;
   __complex__ double res;
-
-  y = __casin (x);
-
-  __real__ res = (double) M_PI_2 - __real__ y;
-  __imag__ res = -__imag__ y;
+  int rcls = fpclassify (__real__ x);
+  int icls = fpclassify (__imag__ x);
+
+  if (rcls <= FP_INFINITE || icls <= FP_INFINITE
+      || (rcls == FP_ZERO && icls == FP_ZERO))
+    {
+      y = __casin (x);
+
+      __real__ res = (double) M_PI_2 - __real__ y;
+      __imag__ res = -__imag__ y;
+    }
+  else
+    {
+      __real__ y = -__imag__ x;
+      __imag__ y = __real__ x;
+
+      y = __kernel_casinh (y, 1);
+
+      __real__ res = __imag__ y;
+      __imag__ res = __real__ y;
+    }
 
   return res;
 }
-- 
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