Imported Upstream version 1.4upstream/1.4

1 files changed, 50 insertions, 0 deletions

diff --git a/src/math/logb.go b/src/math/logb.go
new file mode 100644
index 000000000..f2769d4fd
--- /dev/null
+++ b/src/math/logb.go
@@ -0,0 +1,50 @@
+// 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
+
+// Logb returns the binary exponent of x.
+//
+// Special cases are:
+//	Logb(±Inf) = +Inf
+//	Logb(0) = -Inf
+//	Logb(NaN) = NaN
+func Logb(x float64) float64 {
+	// special cases
+	switch {
+	case x == 0:
+		return Inf(-1)
+	case IsInf(x, 0):
+		return Inf(1)
+	case IsNaN(x):
+		return x
+	}
+	return float64(ilogb(x))
+}
+
+// Ilogb returns the binary exponent of x as an integer.
+//
+// Special cases are:
+//	Ilogb(±Inf) = MaxInt32
+//	Ilogb(0) = MinInt32
+//	Ilogb(NaN) = MaxInt32
+func Ilogb(x float64) int {
+	// special cases
+	switch {
+	case x == 0:
+		return MinInt32
+	case IsNaN(x):
+		return MaxInt32
+	case IsInf(x, 0):
+		return MaxInt32
+	}
+	return ilogb(x)
+}
+
+// logb returns the binary exponent of x. It assumes x is finite and
+// non-zero.
+func ilogb(x float64) int {
+	x, exp := normalize(x)
+	return int((Float64bits(x)>>shift)&mask) - bias + exp
+}