powxi.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 71 行

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*                            Open Watcom Project
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#include "variety.h"
#include "cplx.h"
#include "mathcode.h"
#include "pdiv.h"


_WMRTLINK extended _IF_PowXI( extended base, intstar4 power )
//===========================================================
{
// Return base ** power where power could be <= 0.

    extended    result;

    if( base == 0.0 ) {
        if( power <= 0 ) {
            result = power;
            return( __math2err( FUNC_DPOWI | M_DOMAIN | V_ZERO, &base, &result ) );
        } else {
            return( 0.0 );
        }
    } else {
        if( power < 0 ) {
            power = -power;
            base = PDIV( 1.0, base );
        }
        result = 1.0;
        while( power > 0 ) {
            if( power % 2 == 0 ) {
                base *= base;
                power /= 2;
            } else {
                result *= base;
                --power;
            }
        }
        return( result );
    }
}