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131 lines
3.6 KiB
C
131 lines
3.6 KiB
C
/* raisemod.c: bcmath library file. */
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/*
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Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc.
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Copyright (C) 2000 Philip A. Nelson
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details. (LICENSE)
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to:
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The Free Software Foundation, Inc.
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59 Temple Place, Suite 330
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Boston, MA 02111-1307 USA.
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You may contact the author by:
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e-mail: philnelson@acm.org
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us-mail: Philip A. Nelson
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Computer Science Department, 9062
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Western Washington University
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Bellingham, WA 98226-9062
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*************************************************************************/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <ctype.h>
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#include <stdarg.h>
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#include "bcmath.h"
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#include "private.h"
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/* Truncate a number to zero scale. To avoid sharing issues (refcount and
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shared n_value) the number is copied, this copy is truncated, and the
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original number is "freed". */
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static void
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_bc_truncate (bc_num *num)
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{
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bc_num temp;
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temp = bc_new_num ((*num)->n_len, 0);
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temp->n_sign = (*num)->n_sign;
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memcpy (temp->n_value, (*num)->n_value, (*num)->n_len);
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bc_free_num (num);
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*num = temp;
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}
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/* Raise BASE to the EXPO power, reduced modulo MOD. The result is
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placed in RESULT. If a EXPO is not an integer,
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only the integer part is used. */
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int
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bc_raisemod (bc_num base, bc_num expo, bc_num mod, bc_num *result, int scale)
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{
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bc_num power, exponent, modulus, parity, temp;
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int rscale;
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/* Check for correct numbers. */
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if (bc_is_zero(mod)) return -1;
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if (bc_is_neg(expo)) return -1;
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/* Set initial values. */
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power = bc_copy_num (base);
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exponent = bc_copy_num (expo);
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modulus = bc_copy_num (mod);
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temp = bc_copy_num (BCG(_one_));
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bc_init_num(&parity);
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/* Check the base for scale digits. */
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if (power->n_scale != 0)
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{
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php_error_docref (NULL, E_WARNING, "non-zero scale in base");
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_bc_truncate (&power);
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}
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/* Check the exponent for scale digits. */
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if (exponent->n_scale != 0)
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{
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php_error_docref (NULL, E_WARNING, "non-zero scale in exponent");
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_bc_truncate (&exponent);
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}
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/* Check the modulus for scale digits. */
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if (modulus->n_scale != 0)
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{
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php_error_docref (NULL, E_WARNING, "non-zero scale in modulus");
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_bc_truncate (&modulus);
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}
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/* Do the calculation. */
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rscale = MAX(scale, power->n_scale);
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if ( !bc_compare(modulus, BCG(_one_)) )
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{
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bc_free_num (&temp);
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temp = bc_new_num (1, scale);
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}
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else
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{
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while ( !bc_is_zero(exponent) )
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{
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(void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0);
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if ( !bc_is_zero(parity) )
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{
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bc_multiply (temp, power, &temp, rscale);
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(void) bc_modulo (temp, modulus, &temp, scale);
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}
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bc_multiply (power, power, &power, rscale);
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(void) bc_modulo (power, modulus, &power, scale);
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}
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}
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/* Assign the value. */
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bc_free_num (&power);
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bc_free_num (&exponent);
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bc_free_num (&modulus);
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bc_free_num (result);
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bc_free_num (&parity);
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*result = temp;
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return 0; /* Everything is OK. */
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}
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