无幂函数的浮点数求幂 [英] Floating point exponentiation without power-function
本文介绍了无幂函数的浮点数求幂的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
当前,我必须在电源操作员被窃听的环境中工作.谁能想到一种方法可以暂时解决此错误,并在没有幂函数或运算符的情况下计算a ^ b(两个浮点数)?
Currently I have to work in an environment where the power-operator is bugged. Can anyone think of a method temporarily work around this bug and compute a^b (both floating point) without a power function or operator?
推荐答案
如果有sqrt()可用:
if you have sqrt() available:
double sqr( double x ) { return x * x; }
// meaning of 'precision': the returned answer should be base^x, where
// x is in [power-precision/2,power+precision/2]
double mypow( double base, double power, double precision )
{
if ( power < 0 ) return 1 / mypow( base, -power, precision );
if ( power >= 10 ) return sqr( mypow( base, power/2, precision/2 ) );
if ( power >= 1 ) return base * mypow( base, power-1, precision );
if ( precision >= 1 ) return sqrt( base );
return sqrt( mypow( base, power*2, precision*2 ) );
}
double mypow( double base, double power ) { return mypow( base, power, .000001 ); }
测试代码:
void main()
{
cout.precision( 12 );
cout << mypow( 2.7, 1.23456 ) << endl;
cout << pow ( 2.7, 1.23456 ) << endl;
cout << mypow( 1.001, 1000.7 ) << endl;
cout << pow ( 1.001, 1000.7 ) << endl;
cout << mypow( .3, -10.7 ) << endl;
cout << pow ( .3, -10.7 ) << endl;
cout << mypow( 100000, .00001 ) << endl;
cout << pow ( 100000, .00001 ) << endl;
cout << mypow( 100000, .0000001 ) << endl;
cout << pow ( 100000, .0000001 ) << endl;
}
输出:
3.40835049344
3.40835206431
2.71882549461
2.71882549383
393371.348073
393371.212573
1.00011529225
1.00011513588
1.00000548981
1.00000115129
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