/* raisemod.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. (COPYING.LIB)
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 <config.h>
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdarg.h>
#include "bcmath.h"
#include "private.h"
/* Raise BASE to the EXPO power, reduced modulo MOD. The result is
placed in RESULT. If a EXPO is not an integer,
only the integer part is used. */
int
bc_raisemod (bc_num base, bc_num expo, bc_num mod, bc_num *result, int scale)
{
bc_num power, exponent, modulus, parity, temp;
int rscale;
/* Check for correct numbers. */
if (bc_is_zero(mod)) return -1;
if (bc_is_neg(expo)) return -1;
/* Set initial values. */
power = bc_copy_num (base);
exponent = bc_copy_num (expo);
modulus = bc_copy_num (mod);
temp = bc_copy_num (BCG(_one_));
bc_init_num(&parity);
/* Check the base for scale digits. */
if (power->n_scale != 0)
{
bc_rt_warn ("non-zero scale in base");
bc_divide (power, BCG(_one_), &power, 0); /*truncate */
}
/* Check the exponent for scale digits. */
if (exponent->n_scale != 0)
{
bc_rt_warn ("non-zero scale in exponent");
bc_divide (exponent, BCG(_one_), &exponent, 0); /*truncate */
}
/* Check the modulus for scale digits. */
if (modulus->n_scale != 0)
{
bc_rt_warn ("non-zero scale in modulus");
bc_divide (modulus, BCG(_one_), &modulus, 0); /*truncate */
}
/* Do the calculation. */
rscale = MAX(scale, power->n_scale);
if ( !bc_compare(modulus, BCG(_one_)) )
{
temp = bc_new_num (1, scale);
}
else
{
while ( !bc_is_zero(exponent) )
{
(void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0);
if ( !bc_is_zero(parity) )
{
bc_multiply (temp, power, &temp, rscale);
(void) bc_modulo (temp, modulus, &temp, scale);
}
bc_multiply (power, power, &power, rscale);
(void) bc_modulo (power, modulus, &power, scale);
}
}
/* Assign the value. */
bc_free_num (&power);
bc_free_num (&exponent);
bc_free_num (&modulus);
bc_free_num (result);
bc_free_num (&parity);
*result = temp;
return 0; /* Everything is OK. */
}
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