Imported Upstream version 1.4upstream/1.4

1 files changed, 40 insertions, 0 deletions

diff --git a/src/math/pow10.go b/src/math/pow10.go
new file mode 100644
index 000000000..f5ad28bb4
--- /dev/null
+++ b/src/math/pow10.go
@@ -0,0 +1,40 @@
+// Copyright 2009 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
+
+// This table might overflow 127-bit exponent representations.
+// In that case, truncate it after 1.0e38.
+var pow10tab [70]float64
+
+// Pow10 returns 10**e, the base-10 exponential of e.
+//
+// Special cases are:
+//	Pow10(e) = +Inf for e > 309
+//	Pow10(e) = 0 for e < -324
+func Pow10(e int) float64 {
+	if e <= -325 {
+		return 0
+	} else if e > 309 {
+		return Inf(1)
+	}
+
+	if e < 0 {
+		return 1 / Pow10(-e)
+	}
+	if e < len(pow10tab) {
+		return pow10tab[e]
+	}
+	m := e / 2
+	return Pow10(m) * Pow10(e-m)
+}
+
+func init() {
+	pow10tab[0] = 1.0e0
+	pow10tab[1] = 1.0e1
+	for i := 2; i < len(pow10tab); i++ {
+		m := i / 2
+		pow10tab[i] = pow10tab[m] * pow10tab[i-m]
+	}
+}