Port fdlibm implementation for Math.cosh.

test/mjsunit/es6/math-hyperbolic.js

Index: test/mjsunit/es6/math-hyperbolic.js
diff --git a/test/mjsunit/es6/math-hyperbolic.js b/test/mjsunit/es6/math-hyperbolic.js
index 1632e00b222c5ff277bd385ec1e4d2d15795c59d..8f7164dfef02afeb713014e0818c74e5d9cd4849 100644
--- a/test/mjsunit/es6/math-hyperbolic.js
+++ b/test/mjsunit/es6/math-hyperbolic.js
@@ -166,3 +166,23 @@ assertEquals(Infinity, Math.sinh(710.475860073944));
 assertEquals(-Infinity, Math.sinh(-710.475860073944));
 assertEquals(Infinity, Math.sinh(1000));
 assertEquals(-Infinity, Math.sinh(-1000));
+
+// Implementation-specific tests for cosh.
+// Case |x| < 2^-55
+assertEquals(1, Math.cosh(Math.pow(2, -55)));
+assertEquals(1, Math.cosh(-Math.pow(2, -55)));

[Raymond Toy, 2014/08/29 16:23:31]

Oops. This is a mistake in original test. If we want to test |x| < 2^-55, we
can't use 2^-55.  Replace with 2^-56.

[Yang, 2014/09/01 09:35:42]

Done.

+// Case |x| < 1/2*log(2). cosh(Math.LN2/4) = (sqrt(2)+1)/2^(5/4)
+assertEquals(1.0150517651282178, Math.cosh(Math.LN2/4));
+assertEquals(1.0150517651282178, Math.cosh(-Math.LN2/4));
+// Case 1/2*log(2) < |x| < 22. cosh(10*Math.LN2) = 1048577/2048
+assertEquals(512.00048828125, Math.cosh(10*Math.LN2));
+assertEquals(512.00048828125, Math.cosh(-10*Math.LN2));
+// Case 22 <= |x| < log(maxdouble)
+assertEquals(2.1474836479999983e9, Math.cosh(32*Math.LN2));
+assertEquals(2.1474836479999983e9, Math.cosh(-32*Math.LN2));
+// Case log(maxdouble) <= |x| <= overflowthreshold
+assertEquals(1.7976931348621744e308, Math.cosh(710.4758600739439));
+assertEquals(1.7976931348621744e308, Math.cosh(-710.4758600739439));
+// Overflow.
+assertEquals(Infinity, Math.cosh(710.475860073944));
+assertEquals(Infinity, Math.cosh(-710.475860073944));