powii.c

来自「开放源码的编译器open watcom 1.6.0版的源代码」· C语言 代码 · 共 83 行

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//
// POWII        : power - integer
//

#include "ftnstd.h"
#include "errcod.h"
#include "rtenv.h"
#include "fmthcode.h"


intstar4        PowII( intstar4 base, intstar4 power ) {
//======================================================

// Return base**power where power could be <= 0.

    intstar4  result;

    if( base == 0 ) {
        if( power <= 0 ) {
            return( __imath2err( FUNC_POW | M_DOMAIN | V_ZERO, &base, &power ) );
        } else {
            return( 0 );
        }
    } else {
        if( power < 0 ) {
            if( base == 1 ) {
                return( 1 );
            } else if( base == -1 ) {
                if( power & 1 ) {
                    return( -1 );
                } else {
                    return( 1 );
                }
            } else {
                return( 0 );
            }
        }
        result = 1;
        while( power > 0 ) {
            if( power & 1 ) {
                result *= base;
                --power;
            } else {
                base *= base;
                power /= 2;
            }
        }
        return( result );
    }
}