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44eec946e8
Since `bcpowmod()` does not support non-integral operands, we have to truncate these in addition to emitting a respective warning. We also have to work with the truncated values in the following. We recognize that the division by one to enforce the truncation is actually overkill, but we stick with it for now, and shall tackle the issue for PHP 7.3.
114 lines
3.3 KiB
C
114 lines
3.3 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. (COPYING.LIB)
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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 <assert.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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/* 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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bc_rt_warn ("non-zero scale in base");
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bc_divide (power, BCG(_one_), &power, 0); /*truncate */
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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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bc_rt_warn ("non-zero scale in exponent");
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bc_divide (exponent, BCG(_one_), &exponent, 0); /*truncate */
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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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bc_rt_warn ("non-zero scale in modulus");
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bc_divide (modulus, BCG(_one_), &modulus, 0); /*truncate */
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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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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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