compare.c

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/* compare.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 <stdbool.h>
#include "bcmath.h"
#include "private.h"
#include <stddef.h>
 
 
/* Compare two bc numbers.  Return value is 0 if equal, -1 if N1 is less
   than N2 and +1 if N1 is greater than N2.  If USE_SIGN is false, just
   compare the magnitudes. */
 
bcmath_compare_result _bc_do_compare(bc_num n1, bc_num n2, size_t scale, bool use_sign)
{
    char *n1ptr, *n2ptr;
 
    /* First, compare signs. */
    if (use_sign && n1->n_sign != n2->n_sign) {
        /*
         * scale and n->n_scale differ only in Number objects.
         * This happens when explicitly specify the scale in a Number method.
         */
        if ((n1->n_scale > scale || n2->n_scale > scale) &&
            n1->n_len == 1 && n2->n_len == 1 &&
            n1->n_value[0] == 0 && n2->n_value[0] == 0 &&
            bc_is_zero_for_scale(n1, scale) && bc_is_zero_for_scale(n2, scale)
        ) {
            /* e.g. 0.00 <=> -0.00 */
            return BCMATH_EQUAL;
        }
        if (n1->n_sign == PLUS) {
            /* Positive N1 > Negative N2 */
            return BCMATH_LEFT_GREATER;
        } else {
            /* Negative N1 < Positive N1 */
            return BCMATH_RIGHT_GREATER;
        }
    }
 
    /* Now compare the magnitude. */
    if (n1->n_len != n2->n_len) {
        if (n1->n_len > n2->n_len) {
            /* Magnitude of n1 > n2. */
            if (!use_sign || n1->n_sign == PLUS) {
                return BCMATH_LEFT_GREATER;
            } else {
                return BCMATH_RIGHT_GREATER;
            }
        } else {
            /* Magnitude of n1 < n2. */
            if (!use_sign || n1->n_sign == PLUS) {
                return BCMATH_RIGHT_GREATER;
            } else {
                return BCMATH_LEFT_GREATER;
            }
        }
    }
 
    size_t n1_scale = MIN(n1->n_scale, scale);
    size_t n2_scale = MIN(n2->n_scale, scale);
 
    /* If we get here, they have the same number of integer digits.
       check the integer part and the equal length part of the fraction. */
    size_t count = n1->n_len + MIN (n1_scale, n2_scale);
    n1ptr = n1->n_value;
    n2ptr = n2->n_value;
 
    while ((count > 0) && (*n1ptr == *n2ptr)) {
        n1ptr++;
        n2ptr++;
        count--;
    }
 
    if (count != 0) {
        if (*n1ptr > *n2ptr) {
            /* Magnitude of n1 > n2. */
            if (!use_sign || n1->n_sign == PLUS) {
                return BCMATH_LEFT_GREATER;
            } else {
                return BCMATH_RIGHT_GREATER;
            }
        } else {
            /* Magnitude of n1 < n2. */
            if (!use_sign || n1->n_sign == PLUS) {
                return BCMATH_RIGHT_GREATER;
            } else {
                return BCMATH_LEFT_GREATER;
            }
        }
    }
 
    /* They are equal up to the last part of the equal part of the fraction. */
    if (n1_scale != n2_scale) {
        if (n1_scale > n2_scale) {
            for (count = n1_scale - n2_scale; count > 0; count--) {
                if (*n1ptr++ != 0) {
                    /* Magnitude of n1 > n2. */
                    if (!use_sign || n1->n_sign == PLUS) {
                        return BCMATH_LEFT_GREATER;
                    } else {
                        return BCMATH_RIGHT_GREATER;
                    }
                }
            }
        } else {
            for (count = n2_scale - n1_scale; count > 0; count--) {
                if (*n2ptr++ != 0) {
                    /* Magnitude of n1 < n2. */
                    if (!use_sign || n1->n_sign == PLUS) {
                        return BCMATH_RIGHT_GREATER;
                    } else {
                        return BCMATH_LEFT_GREATER;
                    }
                }
            }
        }
    }
 
    /* They must be equal! */
    return BCMATH_EQUAL;
}
 
 
/* This is the "user callable" routine to compare numbers N1 and N2. */
bcmath_compare_result bc_compare(bc_num n1, bc_num n2, size_t scale)
{
    return _bc_do_compare(n1, n2, scale, true);
}