1 /*****************************************************************************
2 * RRDtool 1.3.8 Copyright by Tobi Oetiker, 1997-2009
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: rrd_diff.c 1801 2009-05-19 13:45:05Z oetiker $
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 #ifdef WIN32
41 #include <ctype.h>
42 #endif
44 double rrd_diff(
45 char *a,
46 char *b)
47 {
48 char res[LAST_DS_LEN + 1], *a1, *b1, *r1, *fix;
49 int c, x, m;
50 char a_neg = 0, b_neg = 0;
51 double result;
53 while (!(isdigit((int) *a) || *a == 0)) {
54 if (*a == '-')
55 a_neg = 1;
56 a++;
57 }
58 fix = a;
59 while (isdigit((int) *fix))
60 fix++;
61 *fix = 0; /* maybe there is some non digit data in the string */
62 while (!(isdigit((int) *b) || *b == 0)) {
63 if (*b == '-')
64 b_neg = 1;
65 b++;
66 }
67 fix = b;
68 while (isdigit((int) *fix))
69 fix++;
70 *fix = 0; /* maybe there is some non digit data in the string */
71 if (!isdigit((int) *a) || !isdigit((int) *b))
72 return DNAN;
73 if (a_neg + b_neg == 1) /* can not handle numbers with different signs yet */
74 return DNAN;
75 a1 = &a[strlen(a) - 1];
76 m = max(strlen(a), strlen(b));
77 if (m > LAST_DS_LEN)
78 return DNAN; /* result string too short */
80 r1 = &res[m + 1];
81 for (b1 = res; b1 <= r1; b1++)
82 *b1 = ' ';
83 b1 = &b[strlen(b) - 1];
84 r1[1] = 0; /* Null terminate result */
85 c = 0;
86 for (x = 0; x < m; x++) {
87 if (a1 >= a && b1 >= b) {
88 *r1 = ((*a1 - c) - *b1) + '0';
89 } else if (a1 >= a) {
90 *r1 = (*a1 - c);
91 } else {
92 *r1 = ('0' - *b1 - c) + '0';
93 }
94 if (*r1 < '0') {
95 *r1 += 10;
96 c = 1;
97 } else if (*r1 > '9') { /* 0 - 10 */
98 *r1 -= 10;
99 c = 1;
100 } else {
101 c = 0;
102 }
103 a1--;
104 b1--;
105 r1--;
106 }
107 if (c) {
108 r1 = &res[m + 1];
109 for (x = 0; isdigit((int) *r1) && x < m; x++, r1--) {
110 *r1 = ('9' - *r1 + c) + '0';
111 if (*r1 > '9') {
112 *r1 -= 10;
113 c = 1;
114 } else {
115 c = 0;
116 }
117 }
118 result = -atof(res);
119 } else
120 result = atof(res);
122 if (a_neg + b_neg == 2) /* both are negatives, reverse sign */
123 result = -result;
125 return result;
126 }