math: add functions Log2, Nextafter, Fdim, Fmax, Fmin

Add functions, tests and benchmarks. Fix typos in comments
in expm1 and hypot_386.  Fix Acosh domain error in benchmark
test.

R=rsc
CC=golang-dev
http://codereview.appspot.com/204069

Committer: Russ Cox <rsc@golang.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/src/pkg/math/nextafter.go b/src/pkg/math/nextafter.go
new file mode 100644
index 000000000..b57d3e715
--- /dev/null
+++ b/src/pkg/math/nextafter.go
@@ -0,0 +1,27 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+// Nextafter returns the next representable value after x towards y.
+// If x == y, then x is returned.
+//
+// Special cases are:
+//	Nextafter(NaN, y) = NaN
+//	Nextafter(x, NaN) = NaN
+func Nextafter(x, y float64) (r float64) {
+	switch {
+	case IsNaN(x) || IsNaN(y): // special case
+		r = NaN()
+	case x == y:
+		r = x
+	case x == 0:
+		r = Copysign(Float64frombits(1), y)
+	case (y > x) == (x > 0):
+		r = Float64frombits(Float64bits(x) + 1)
+	default:
+		r = Float64frombits(Float64bits(x) - 1)
+	}
+	return r
+}