1 /*****************************************************************************
2 * RRDtool 1.2.1 Copyright by Tobi Oetiker, 1997-2005
3 * This code is stolen from rateup (mrtg-2.x) by Dave Rand
4 *****************************************************************************
5 * diff calculate the difference between two very long integers available as
6 * strings
7 *****************************************************************************
8 * $Id$
9 * $Log$
10 * Revision 1.4 2003/03/10 00:30:34 oetiker
11 * handle cases with two negative numbers
12 * -- Sasha Mikheev <sasha@avalon-net.co.il>
13 *
14 * Revision 1.3 2002/04/01 18:31:22 oetiker
15 * "!" takes a higher preference than "||" this means rrd_update N:: would
16 * segfault -- Oliver Cook <ollie@uk.clara.net>
17 *
18 * Revision 1.2 2002/02/01 20:34:49 oetiker
19 * fixed version number and date/time
20 *
21 * Revision 1.1.1.1 2001/02/25 22:25:05 oetiker
22 * checkin
23 *
24 * Revision 1.1 1998/10/08 18:21:45 oetiker
25 * Initial revision
26 *
27 * Revision 1.3 1998/02/06 21:10:52 oetiker
28 * removed max define .. it is now in rrd_tool.h
29 *
30 * Revision 1.2 1997/12/07 20:38:03 oetiker
31 * ansified
32 *
33 * Revision 1.1 1997/11/28 23:31:59 oetiker
34 * Initial revision
35 *
36 *****************************************************************************/
38 #include "rrd_tool.h"
40 double
41 rrd_diff(char *a, char *b)
42 {
43 char res[LAST_DS_LEN+1], *a1, *b1, *r1, *fix;
44 int c,x,m;
45 char a_neg=0, b_neg=0;
46 double result;
48 while (!(isdigit((int)*a) || *a==0)) {
49 if(*a=='-')
50 a_neg = 1;
51 a++;
52 }
53 fix=a;
54 while (isdigit((int)*fix))
55 fix++;
56 *fix = 0; /* maybe there is some non digit data in the string */
57 while (!(isdigit((int)*b) || *b==0)) {
58 if(*b=='-')
59 b_neg = 1;
60 b++;
61 }
62 fix=b;
63 while (isdigit((int)*fix))
64 fix++;
65 *fix = 0; /* maybe there is some non digit data in the string */
66 if(!isdigit((int)*a) || !isdigit((int)*b))
67 return DNAN;
68 if(a_neg+b_neg == 1) /* can not handle numbers with different signs yet */
69 return DNAN;
70 a1 = &a[strlen(a)-1];
71 m = max(strlen(a),strlen(b));
72 if (m > LAST_DS_LEN) return DNAN; /* result string too short */
74 r1 = &res[m+1];
75 for (b1 = res;b1 <= r1; b1++) *b1 = ' ';
76 b1 = &b[strlen(b)-1];
77 r1[1] = 0; /* Null terminate result */
78 c = 0;
79 for (x=0; x<m; x++) {
80 if (a1 >= a && b1 >= b) {
81 *r1 = ((*a1 - c) - *b1) + '0';
82 } else if (a1 >= a) {
83 *r1 = (*a1 - c);
84 } else {
85 *r1 = ('0' - *b1 - c) + '0';
86 }
87 if (*r1 < '0') {
88 *r1 += 10;
89 c=1;
90 } else
91 if (*r1 > '9') { /* 0 - 10 */
92 *r1 -= 10;
93 c=1;
94 } else {
95 c=0;
96 }
97 a1--;b1--;r1--;
98 }
99 if (c) {
100 r1 = &res[m+1];
101 for (x=0; isdigit((int)*r1) && x<m; x++,r1--) {
102 *r1 = ('9' - *r1 + c) + '0';
103 if (*r1 > '9') {
104 *r1 -= 10;
105 c=1;
106 } else {
107 c=0;
108 }
109 }
110 result = -atof(res);
111 } else
112 result = atof(res);
114 if(a_neg+b_neg==2) /* both are negatives, reverse sign */
115 result = -result;
117 return result;
118 }