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1.1 misho 1: /* raisemod.c: bcmath library file. */ 2: /* 3: Copyright (C) 1991, 1992, 1993, 1994, 1997 Free Software Foundation, Inc. 4: Copyright (C) 2000 Philip A. Nelson 5: 6: This library is free software; you can redistribute it and/or 7: modify it under the terms of the GNU Lesser General Public 8: License as published by the Free Software Foundation; either 9: version 2 of the License, or (at your option) any later version. 10: 11: This library is distributed in the hope that it will be useful, 12: but WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: Lesser General Public License for more details. (COPYING.LIB) 15: 16: You should have received a copy of the GNU Lesser General Public 17: License along with this library; if not, write to: 18: 19: The Free Software Foundation, Inc. 20: 59 Temple Place, Suite 330 21: Boston, MA 02111-1307 USA. 22: 23: You may contact the author by: 24: e-mail: philnelson@acm.org 25: us-mail: Philip A. Nelson 26: Computer Science Department, 9062 27: Western Washington University 28: Bellingham, WA 98226-9062 29: 30: *************************************************************************/ 31: 32: #include <config.h> 33: #include <stdio.h> 34: #include <assert.h> 35: #include <stdlib.h> 36: #include <ctype.h> 37: #include <stdarg.h> 38: #include "bcmath.h" 39: #include "private.h" 40: 41: /* Raise BASE to the EXPO power, reduced modulo MOD. The result is 42: placed in RESULT. If a EXPO is not an integer, 43: only the integer part is used. */ 44: 45: int 46: bc_raisemod (bc_num base, bc_num expo, bc_num mod, bc_num *result, int scale TSRMLS_DC) 47: { 48: bc_num power, exponent, parity, temp; 49: int rscale; 50: 51: /* Check for correct numbers. */ 52: if (bc_is_zero(mod TSRMLS_CC)) return -1; 53: if (bc_is_neg(expo)) return -1; 54: 55: /* Set initial values. */ 56: power = bc_copy_num (base); 57: exponent = bc_copy_num (expo); 58: temp = bc_copy_num (BCG(_one_)); 59: bc_init_num(&parity TSRMLS_CC); 60: 61: /* Check the base for scale digits. */ 62: if (base->n_scale != 0) 63: bc_rt_warn ("non-zero scale in base"); 64: 65: /* Check the exponent for scale digits. */ 66: if (exponent->n_scale != 0) 67: { 68: bc_rt_warn ("non-zero scale in exponent"); 69: bc_divide (exponent, BCG(_one_), &exponent, 0 TSRMLS_CC); /*truncate */ 70: } 71: 72: /* Check the modulus for scale digits. */ 73: if (mod->n_scale != 0) 74: bc_rt_warn ("non-zero scale in modulus"); 75: 76: /* Do the calculation. */ 77: rscale = MAX(scale, base->n_scale); 78: while ( !bc_is_zero(exponent TSRMLS_CC) ) 79: { 80: (void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0 TSRMLS_CC); 81: if ( !bc_is_zero(parity TSRMLS_CC) ) 82: { 83: bc_multiply (temp, power, &temp, rscale TSRMLS_CC); 84: (void) bc_modulo (temp, mod, &temp, scale TSRMLS_CC); 85: } 86: 87: bc_multiply (power, power, &power, rscale TSRMLS_CC); 88: (void) bc_modulo (power, mod, &power, scale TSRMLS_CC); 89: } 90: 91: /* Assign the value. */ 92: bc_free_num (&power); 93: bc_free_num (&exponent); 94: bc_free_num (result); 95: bc_free_num (&parity); 96: *result = temp; 97: return 0; /* Everything is OK. */ 98: }