sub.c

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/* sub.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.  (LICENSE)
 
    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 "bcmath.h"
#include "private.h"
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
 
/* Here is the full subtract routine that takes care of negative numbers.
   N2 is subtracted from N1 and the result placed in RESULT.  SCALE_MIN
   is the minimum scale for the result. */
 
bc_num bc_sub(bc_num n1, bc_num n2, size_t scale_min)
{
    bc_num diff = NULL;
 
    if (n1->n_sign != n2->n_sign) {
        diff = _bc_do_add(n1, n2);
        diff->n_sign = n1->n_sign;
    } else {
        /* subtraction must be done. */
        /* Compare magnitudes. */
        switch (_bc_do_compare(n1, n2, scale_min, false)) {
            case BCMATH_RIGHT_GREATER:
                /* n1 is less than n2, subtract n1 from n2. */
                diff = _bc_do_sub(n2, n1);
                diff->n_sign = (n2->n_sign == PLUS ? MINUS : PLUS);
                break;
            case BCMATH_EQUAL: {
                /* They are equal! return zero! */
                size_t res_scale = MAX (scale_min, MAX(n1->n_scale, n2->n_scale));
                diff = bc_new_num (1, res_scale);
                break;
            }
            case BCMATH_LEFT_GREATER:
                /* n2 is less than n1, subtract n2 from n1. */
                diff = _bc_do_sub(n1, n2);
                diff->n_sign = n1->n_sign;
                break;
        }
    }
 
    return diff;
}