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| author | Rob Pike <r@golang.org> | 2009-06-09 09:53:44 -0700 |
|---|---|---|
| committer | Rob Pike <r@golang.org> | 2009-06-09 09:53:44 -0700 |
| commit | 7249ea4df2b4f12a4e7ed446f270cea87e4ffd34 (patch) | |
| tree | 7032a11d0cac2ae4d3e90f7a189b575b5a50f848 /src/pkg/math/pow10.go | |
| parent | acf6ef7a82b3fe61516a1bac4563706552bdf078 (diff) | |
| download | golang-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.go | 37 |
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]; + } +} |
