raise.c

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/* raise.c: bcmath library file. */
/*
    Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc.
    Copyright (C) 2000 Philip A. Nelson
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.
 
    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.  (LICENSE)
 
    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to:
 
      The Free Software Foundation, Inc.
      59 Temple Place, Suite 330
      Boston, MA 02111-1307 USA.
 
    You may contact the author by:
       e-mail:  philnelson@acm.org
      us-mail:  Philip A. Nelson
                Computer Science Department, 9062
                Western Washington University
                Bellingham, WA 98226-9062
 
*************************************************************************/
 
#include "bcmath.h"
#include <assert.h>
#include <stdbool.h>
#include <stddef.h>
 
void bc_square_ex(bc_num n1, bc_num *result, size_t scale_min) {
    bc_num square_ex = bc_square(n1, scale_min);
    bc_free_num(result);
    *(result) = square_ex;
}
 
/* Raise "base" to the "exponent" power.  The result is placed in RESULT.
   Maximum exponent is LONG_MAX.  If a "exponent" is not an integer,
   only the integer part is used.  */
bool bc_raise(bc_num base, long exponent, bc_num *result, size_t scale) {
    bc_num temp, power;
    size_t rscale;
    size_t pwrscale;
    size_t calcscale;
    bool is_neg;
 
    /* Special case if exponent is a zero. */
    if (exponent == 0) {
        bc_free_num (result);
        *result = bc_copy_num(BCG(_one_));
        return true;
    }
 
    /* Other initializations. */
    if (exponent < 0) {
        is_neg = true;
        exponent = -exponent;
        rscale = scale;
    } else {
        is_neg = false;
        rscale = MIN (base->n_scale * exponent, MAX(scale, base->n_scale));
    }
 
    /* Set initial value of temp. */
    power = bc_copy_num(base);
    pwrscale = base->n_scale;
    while ((exponent & 1) == 0) {
        pwrscale = 2 * pwrscale;
        bc_square_ex(power, &power, pwrscale);
        exponent = exponent >> 1;
    }
    temp = bc_copy_num(power);
    calcscale = pwrscale;
    exponent = exponent >> 1;
 
    /* Do the calculation. */
    while (exponent > 0) {
        pwrscale = 2 * pwrscale;
        bc_square_ex(power, &power, pwrscale);
        if ((exponent & 1) == 1) {
            calcscale = pwrscale + calcscale;
            bc_multiply_ex(temp, power, &temp, calcscale);
        }
        exponent = exponent >> 1;
    }
 
    /* Assign the value. */
    if (is_neg) {
        if (bc_divide(BCG(_one_), temp, result, rscale) == false) {
            bc_free_num (&temp);
            bc_free_num (&power);
            return false;
        }
        bc_free_num (&temp);
    } else {
        bc_free_num (result);
        *result = temp;
        (*result)->n_scale = MIN(scale, (*result)->n_scale);
    }
    bc_free_num (&power);
    return true;
}
 
/* This is used internally by BCMath */
void bc_raise_bc_exponent(bc_num base, bc_num expo, bc_num *result, size_t scale) {
    /* Exponent must not have fractional part */
    assert(expo->n_scale == 0);
 
    long exponent = bc_num2long(expo);
    /* Exponent must be properly convertable to long */
    if (exponent == 0 && (expo->n_len > 1 || expo->n_value[0] != 0)) {
        assert(false && "Exponent is not well formed in internal call");
        //assert(exponent != 0 || (expo->n_len == 0 && expo->n_value[0] == 0));
    }
    //assert(exponent != 0 || (expo->n_len == 0 && expo->n_value[0] == 0));
    bc_raise(base, exponent, result, scale);
}