1 files changed, 42 insertions, 0 deletions
diff --git a/sysdeps/generic/acos.c b/sysdeps/generic/acos.c
new file mode 100644
index 0000000000..c77c9faf1f
--- /dev/null
+++ b/sysdeps/generic/acos.c
@@ -0,0 +1,42 @@
+/* Copyright (C) 1991 Free Software Foundation, Inc.
+This file is part of the GNU C Library.
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public License as
+published by the Free Software Foundation; either version 2 of the
+License, or (at your option) any later version.
+
+The GNU C Library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.  */
+
+#include <ansidecl.h>
+#include <errno.h>
+#include <math.h>
+
+/* Return the inverse cosine of X.  */
+double
+DEFUN(acos, (x), double x)
+{
+  double t;
+
+  if (__isnan(x))
+    {
+      errno = EDOM;
+      return x;
+    }
+
+  if (x == -1.0)
+    /* If X is -1, the general formula blows up (zero divided by zero loses),
+       but we know that acos(-1) = pi.  */
+    t = atan2(1.0, 0.0);
+  else
+    t = atan2(sqrt((1.0 - x) / (1.0 + x)), 1.0);
+  return t + t;
+}