1 /* doaddsub.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.  (LICENSE)
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 <stdlib.h>
35 #include <ctype.h>
36 #include <stdarg.h>
37 #include "bcmath.h"
38 #include "private.h"
39 
40 
41 /* Perform addition: N1 is added to N2 and the value is
42    returned.  The signs of N1 and N2 are ignored.
43    SCALE_MIN is to set the minimum scale of the result. */
44 
45  bc_num
_bc_do_addnull46 _bc_do_add (n1, n2, scale_min)
47      bc_num n1, n2;
48      int scale_min;
49 {
50   bc_num sum;
51   int sum_scale, sum_digits;
52   char *n1ptr, *n2ptr, *sumptr;
53   int carry, n1bytes, n2bytes;
54   int count;
55 
56   /* Prepare sum. */
57   sum_scale = MAX (n1->n_scale, n2->n_scale);
58   sum_digits = MAX (n1->n_len, n2->n_len) + 1;
59   sum = bc_new_num (sum_digits, MAX(sum_scale, scale_min));
60 
61   /* Zero extra digits made by scale_min. */
62   if (scale_min > sum_scale)
63     {
64       sumptr = (char *) (sum->n_value + sum_scale + sum_digits);
65       for (count = scale_min - sum_scale; count > 0; count--)
66 	*sumptr++ = 0;
67     }
68 
69   /* Start with the fraction part.  Initialize the pointers. */
70   n1bytes = n1->n_scale;
71   n2bytes = n2->n_scale;
72   n1ptr = (char *) (n1->n_value + n1->n_len + n1bytes - 1);
73   n2ptr = (char *) (n2->n_value + n2->n_len + n2bytes - 1);
74   sumptr = (char *) (sum->n_value + sum_scale + sum_digits - 1);
75 
76   /* Add the fraction part.  First copy the longer fraction.*/
77   if (n1bytes != n2bytes)
78     {
79       if (n1bytes > n2bytes)
80 	while (n1bytes>n2bytes)
81 	  { *sumptr-- = *n1ptr--; n1bytes--;}
82       else
83 	while (n2bytes>n1bytes)
84 	  { *sumptr-- = *n2ptr--; n2bytes--;}
85     }
86 
87   /* Now add the remaining fraction part and equal size integer parts. */
88   n1bytes += n1->n_len;
89   n2bytes += n2->n_len;
90   carry = 0;
91   while ((n1bytes > 0) && (n2bytes > 0))
92     {
93       *sumptr = *n1ptr-- + *n2ptr-- + carry;
94       if (*sumptr > (BASE-1))
95 	{
96 	   carry = 1;
97 	   *sumptr -= BASE;
98 	}
99       else
100 	carry = 0;
101       sumptr--;
102       n1bytes--;
103       n2bytes--;
104     }
105 
106   /* Now add carry the longer integer part. */
107   if (n1bytes == 0)
108     { n1bytes = n2bytes; n1ptr = n2ptr; }
109   while (n1bytes-- > 0)
110     {
111       *sumptr = *n1ptr-- + carry;
112       if (*sumptr > (BASE-1))
113 	{
114 	   carry = 1;
115 	   *sumptr -= BASE;
116 	 }
117       else
118 	carry = 0;
119       sumptr--;
120     }
121 
122   /* Set final carry. */
123   if (carry == 1)
124     *sumptr += 1;
125 
126   /* Adjust sum and return. */
127   _bc_rm_leading_zeros (sum);
128   return sum;
129 }
130 
131 
132 /* Perform subtraction: N2 is subtracted from N1 and the value is
133    returned.  The signs of N1 and N2 are ignored.  Also, N1 is
134    assumed to be larger than N2.  SCALE_MIN is the minimum scale
135    of the result. */
136 
137  bc_num
_bc_do_subnull138 _bc_do_sub (n1, n2, scale_min)
139      bc_num n1, n2;
140      int scale_min;
141 {
142   bc_num diff;
143   int diff_scale, diff_len;
144   int min_scale, min_len;
145   char *n1ptr, *n2ptr, *diffptr;
146   int borrow, count, val;
147 
148   /* Allocate temporary storage. */
149   diff_len = MAX (n1->n_len, n2->n_len);
150   diff_scale = MAX (n1->n_scale, n2->n_scale);
151   min_len = MIN  (n1->n_len, n2->n_len);
152   min_scale = MIN (n1->n_scale, n2->n_scale);
153   diff = bc_new_num (diff_len, MAX(diff_scale, scale_min));
154 
155   /* Zero extra digits made by scale_min. */
156   if (scale_min > diff_scale)
157     {
158       diffptr = (char *) (diff->n_value + diff_len + diff_scale);
159       for (count = scale_min - diff_scale; count > 0; count--)
160 	*diffptr++ = 0;
161     }
162 
163   /* Initialize the subtract. */
164   n1ptr = (char *) (n1->n_value + n1->n_len + n1->n_scale -1);
165   n2ptr = (char *) (n2->n_value + n2->n_len + n2->n_scale -1);
166   diffptr = (char *) (diff->n_value + diff_len + diff_scale -1);
167 
168   /* Subtract the numbers. */
169   borrow = 0;
170 
171   /* Take care of the longer scaled number. */
172   if (n1->n_scale != min_scale)
173     {
174       /* n1 has the longer scale */
175       for (count = n1->n_scale - min_scale; count > 0; count--)
176 	*diffptr-- = *n1ptr--;
177     }
178   else
179     {
180       /* n2 has the longer scale */
181       for (count = n2->n_scale - min_scale; count > 0; count--)
182 	{
183 	  val = - *n2ptr-- - borrow;
184 	  if (val < 0)
185 	    {
186 	      val += BASE;
187 	      borrow = 1;
188 	    }
189 	  else
190 	    borrow = 0;
191 	  *diffptr-- = val;
192 	}
193     }
194 
195   /* Now do the equal length scale and integer parts. */
196 
197   for (count = 0; count < min_len + min_scale; count++)
198     {
199       val = *n1ptr-- - *n2ptr-- - borrow;
200       if (val < 0)
201 	{
202 	  val += BASE;
203 	  borrow = 1;
204 	}
205       else
206 	borrow = 0;
207       *diffptr-- = val;
208     }
209 
210   /* If n1 has more digits then n2, we now do that subtract. */
211   if (diff_len != min_len)
212     {
213       for (count = diff_len - min_len; count > 0; count--)
214 	{
215 	  val = *n1ptr-- - borrow;
216 	  if (val < 0)
217 	    {
218 	      val += BASE;
219 	      borrow = 1;
220 	    }
221 	  else
222 	    borrow = 0;
223 	  *diffptr-- = val;
224 	}
225     }
226 
227   /* Clean up and return. */
228   _bc_rm_leading_zeros (diff);
229   return diff;
230 }
231