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authorRob Pike <r@golang.org>2009-06-09 09:53:44 -0700
committerRob Pike <r@golang.org>2009-06-09 09:53:44 -0700
commit7249ea4df2b4f12a4e7ed446f270cea87e4ffd34 (patch)
tree7032a11d0cac2ae4d3e90f7a189b575b5a50f848 /src/pkg/math/pow10.go
parentacf6ef7a82b3fe61516a1bac4563706552bdf078 (diff)
downloadgolang-7249ea4df2b4f12a4e7ed446f270cea87e4ffd34.tar.gz
mv src/lib to src/pkg
tests: all.bash passes, gobuild still works, godoc still works. R=rsc OCL=30096 CL=30102
Diffstat (limited to 'src/pkg/math/pow10.go')
-rw-r--r--src/pkg/math/pow10.go37
1 files changed, 37 insertions, 0 deletions
diff --git a/src/pkg/math/pow10.go b/src/pkg/math/pow10.go
new file mode 100644
index 000000000..fcdd6e0a1
--- /dev/null
+++ b/src/pkg/math/pow10.go
@@ -0,0 +1,37 @@
+// 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.
+ * it is important to get all one can from this
+ * routine since it is used in atof to scale numbers.
+ * the presumption is that GO converts fp numbers better
+ * than multipication of lower powers of 10.
+ */
+
+var pow10tab [70]float64;
+
+// Pow10 returns 10**x, the base-10 exponential of x.
+func Pow10(e int) float64 {
+ 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];
+ }
+}