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               0 : {
      48                 :   bc_num power, exponent, parity, temp;
      49                 :   int rscale;
      50                 : 
      51                 :   /* Check for correct numbers. */
      52               0 :   if (bc_is_zero(mod TSRMLS_CC)) return -1;
      53               0 :   if (bc_is_neg(expo)) return -1;
      54                 : 
      55                 :   /* Set initial values.  */
      56               0 :   power = bc_copy_num (base);
      57               0 :   exponent = bc_copy_num (expo);
      58               0 :   temp = bc_copy_num (BCG(_one_));
      59               0 :   bc_init_num(&parity TSRMLS_CC);
      60                 : 
      61                 :   /* Check the base for scale digits. */
      62               0 :   if (base->n_scale != 0)
      63               0 :       bc_rt_warn ("non-zero scale in base");
      64                 : 
      65                 :   /* Check the exponent for scale digits. */
      66               0 :   if (exponent->n_scale != 0)
      67                 :     {
      68               0 :       bc_rt_warn ("non-zero scale in exponent");
      69               0 :       bc_divide (exponent, BCG(_one_), &exponent, 0 TSRMLS_CC); /*truncate */
      70                 :     }
      71                 : 
      72                 :   /* Check the modulus for scale digits. */
      73               0 :   if (mod->n_scale != 0)
      74               0 :       bc_rt_warn ("non-zero scale in modulus");
      75                 : 
      76                 :   /* Do the calculation. */
      77               0 :   rscale = MAX(scale, base->n_scale);
      78               0 :   while ( !bc_is_zero(exponent TSRMLS_CC) )
      79                 :     {
      80               0 :       (void) bc_divmod (exponent, BCG(_two_), &exponent, &parity, 0 TSRMLS_CC);
      81               0 :       if ( !bc_is_zero(parity TSRMLS_CC) )
      82                 :         {
      83               0 :           bc_multiply (temp, power, &temp, rscale TSRMLS_CC);
      84               0 :           (void) bc_modulo (temp, mod, &temp, scale TSRMLS_CC);
      85                 :         }
      86                 : 
      87               0 :       bc_multiply (power, power, &power, rscale TSRMLS_CC);
      88               0 :       (void) bc_modulo (power, mod, &power, scale TSRMLS_CC);
      89                 :     }
      90                 : 
      91                 :   /* Assign the value. */
      92               0 :   bc_free_num (&power);
      93               0 :   bc_free_num (&exponent);
      94               0 :   bc_free_num (result);
      95               0 :   bc_free_num (&parity);
      96               0 :   *result = temp;
      97               0 :   return 0;     /* Everything is OK. */
      98                 : }