lapo.it
1// Hex JavaScript decoder
2// Copyright (c) 2008 Lapo Luchini <lapo@lapo.it>
3
4// Permission to use, copy, modify, and/or distribute this software for any
5// purpose with or without fee is hereby granted, provided that the above
6// copyright notice and this permission notice appear in all copies.
7//
8// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15
16const
17 haveU8 = (typeof Uint8Array == 'function');
18
19let decoder; // populated on first usage
20
21export class Hex {
22
23 /**
24 * Decodes an hexadecimal value.
25 * @param {string|Array|Uint8Array} a - a string representing hexadecimal data, or an array representation of its charcodes
26 */
27 static decode(a) {
28 let isString = (typeof a == 'string');
29 let i;
30 if (decoder === undefined) {
31 let hex = '0123456789ABCDEF',
32 ignore = ' \f\n\r\t\u00A0\u2028\u2029';
33 decoder = [];
34 for (i = 0; i < 16; ++i)
35 decoder[hex.charCodeAt(i)] = i;
36 hex = hex.toLowerCase();
37 for (i = 10; i < 16; ++i)
38 decoder[hex.charCodeAt(i)] = i;
39 for (i = 0; i < ignore.length; ++i)
40 decoder[ignore.charCodeAt(i)] = -1;
41 }
42 let out = haveU8 ? new Uint8Array(a.length >> 1) : [],
43 bits = 0,
44 char_count = 0,
45 len = 0;
46 for (i = 0; i < a.length; ++i) {
47 let c = isString ? a.charCodeAt(i) : a[i];
48 c = decoder[c];
49 if (c == -1)
50 continue;
51 if (c === undefined)
52 throw 'Illegal character at offset ' + i;
53 bits |= c;
54 if (++char_count >= 2) {
55 out[len++] = bits;
56 bits = 0;
57 char_count = 0;
58 } else {
59 bits <<= 4;
60 }
61 }
62 if (char_count)
63 throw 'Hex encoding incomplete: 4 bits missing';
64 if (haveU8 && out.length > len) // in case it was originally longer because of ignored characters
65 out = out.subarray(0, len);
66 return out;
67 }
68
69}