/* 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 TSRMLS_DC) { bc_num power, exponent, parity, temp; int rscale; /* Check for correct numbers. */ if (bc_is_zero(mod TSRMLS_CC)) return -1; if (bc_is_neg(expo)) return -1; /* Set initial values. */ power = bc_copy_num (base); exponent = bc_copy_num (expo); temp = bc_copy_num (BCG(_one_)); bc_init_num(&parity TSRMLS_CC); /* Check the base for scale digits. */ if (base->n_scale != 0) bc_rt_warn ("non-zero scale in base"); /* 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 TSRMLS_CC); /*truncate */ } /* Check the modulus for scale digits. */ if (mod->n_scale != 0) bc_rt_warn ("non-zero scale in modulus"); /* Do the calculation. */ rscale = MAX(scale, base->n_scale); while ( !bc_is_zero(exponent TSRMLS_CC) ) { (void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0 TSRMLS_CC); if ( !bc_is_zero(parity TSRMLS_CC) ) { bc_multiply (temp, power, &temp, rscale TSRMLS_CC); (void) bc_modulo (temp, mod, &temp, scale TSRMLS_CC); } bc_multiply (power, power, &power, rscale TSRMLS_CC); (void) bc_modulo (power, mod, &power, scale TSRMLS_CC); } /* Assign the value. */ bc_free_num (&power); bc_free_num (&exponent); bc_free_num (result); bc_free_num (&parity); *result = temp; return 0; /* Everything is OK. */ }