Source file src/pkg/math/pow10.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package math
     6	
     7	// This table might overflow 127-bit exponent representations.
     8	// In that case, truncate it after 1.0e38.
     9	var pow10tab [70]float64
    10	
    11	// Pow10 returns 10**e, the base-10 exponential of e.
    12	//
    13	// Special cases are:
    14	//	Pow10(e) = +Inf for e > 309
    15	//	Pow10(e) = 0 for e < -324
    16	func Pow10(e int) float64 {
    17		if e <= -325 {
    18			return 0
    19		} else if e > 309 {
    20			return Inf(1)
    21		}
    22	
    23		if e < 0 {
    24			return 1 / Pow10(-e)
    25		}
    26		if e < len(pow10tab) {
    27			return pow10tab[e]
    28		}
    29		m := e / 2
    30		return Pow10(m) * Pow10(e-m)
    31	}
    32	
    33	func init() {
    34		pow10tab[0] = 1.0e0
    35		pow10tab[1] = 1.0e1
    36		for i := 2; i < len(pow10tab); i++ {
    37			m := i / 2
    38			pow10tab[i] = pow10tab[m] * pow10tab[i-m]
    39		}
    40	}