go/src/lib/math/pow10.go

// 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

export	pow10

/*
 * 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.
 */
const
(
	tabsize		= 70;
)

var	tab[tabsize] double;
func	init();
var	initdone bool;

//{
//	1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9,
//	1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19,
//	1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29,
//	1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39,
//	1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49,
//	1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59,
//	1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69,
//};

func
pow10(e int) double 
{
	if !initdone {
		init();
	}
	if e < 0 {
		return 1/pow10(-e);
	}
	if e < tabsize {
		return tab[e];
	}
	m := e/2;
	return pow10(m) * pow10(e-m);
}

func
init()
{
	initdone = true;
	tab[0] = 1.0;
	for i:=1; i<tabsize; i=i+1 {
		tab[i] = tab[i-1]*10;
	}
}