Home
base64.c - ics2txt - convert icalendar .ics file to plain text
HTML git clone git://bitreich.org/ics2txt git://enlrupgkhuxnvlhsf6lc3fziv5h2hhfrinws65d7roiv6bfj7d652fid.onion/ics2txt
DIR Log
DIR Files
DIR Refs
DIR Tags
DIR README
---
base64.c (3039B)
---
1 #include "base64.h"
2 #include <assert.h>
3 #include <stddef.h>
4 #include <stdint.h>
5 #include <string.h>
6
7 static char encode_map[64] =
8 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
9
10 void
11 base64_encode(char const *s, size_t slen, char *d, size_t *dlen)
12 {
13 char const *sbeg = s, *send = s + slen, *dbeg = d;
14 unsigned char x;
15
16 while (s < send) {
17 switch ((s - sbeg) % 3) {
18 case 0: /* AAAAAABB bbbbcccc ccdddddd */
19 assert((size_t)(d - dbeg) + 1 < *dlen);
20 *d++ = encode_map[*s >> 2];
21 x = *s << 4 & 0x3f;
22 break;
23 case 1: /* aaaaaabb BBBBCCCC ccdddddd */
24 assert((size_t)(d - dbeg) + 1 < *dlen);
25 *d++ = encode_map[x | (*s >> 4)];
26 x = (*s << 2) & 0x3f;
27 break;
28 case 2: /* aaaaaabb bbbbcccc CCDDDDDD */
29 assert((size_t)(d - dbeg) + 2 < *dlen);
30 *d++ = encode_map[x | (*s >> 6)];
31 *d++ = encode_map[*s & 0x3f];
32 break;
33 }
34 s++;
35 }
36
37 /* flush extra content in 'x' */
38 assert((size_t)(d - dbeg) + 1 < *dlen);
39 if ((s - sbeg) % 3 != 2)
40 *d++ = encode_map[x];
41
42 /* pad the end with '=' */
43 while ((d - dbeg) % 4 != 0) {
44 assert((size_t)(d - dbeg) + 1 < *dlen);
45 *d++ = '=';
46 }
47
48 *dlen = d - dbeg;
49 }
50
51 static int8_t decode_map[256] = {
52 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
53 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
54 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
55 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, 0, -1, -1,
56 -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
57 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
58 -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
59 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
60 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
61 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
62 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
63 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
64 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
65 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
66 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
67 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
68 };
69
70 int
71 base64_decode(char const *s, size_t *slen, char *d, size_t *dlen)
72 {
73 char const *sbeg = s, *send = sbeg + *slen, *dbeg = d;
74
75 for (; s + 3 < send; s += 4) {
76 int8_t x0 = decode_map[(unsigned)s[0]];
77 int8_t x1 = decode_map[(unsigned)s[1]];
78 int8_t x2 = decode_map[(unsigned)s[2]];
79 int8_t x3 = decode_map[(unsigned)s[3]];
80 uint32_t x = (x0 << 18) | (x1 << 12) | (x2 << 6) | (x3 << 0);
81
82 assert((size_t)(d - dbeg) + 3 < *dlen);
83 *d++ = x >> 16;
84 *d++ = x >> 8 & 0xff;
85 *d++ = x & 0xff;
86
87 /* only "xxxx" or "xxx=" or "xx==" allowed */
88 if (s[0] == '=' || s[1] == '=' || (s[2] == '=' && s[3] != '='))
89 return -2;
90 if (s[2] == '=')
91 d--;
92 if (s[3] == '=') {
93 d--;
94 break;
95 }
96
97 if (x0 < 0 || x1 < 0 || x2 < 0 || x3 < 0)
98 return -1;
99 }
100
101 *slen = s - sbeg;
102 *dlen = d - dbeg;
103 return 0;
104 }