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comparison mercurial/base85.c @ 3279:1f2c3983a6c5

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Add a base85 codec
author Brendan Cully <brendan@kublai.com>
date Fri, 06 Oct 2006 13:01:54 -0700
parents
children e93c926e069e
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3278:4b2d3c8a6195 3279:1f2c3983a6c5
1 /*
2 base85 codec
3
4 Copyright 2006 Brendan Cully <brendan@kublai.com>
5
6 This software may be used and distributed according to the terms of
7 the GNU General Public License, incorporated herein by reference.
8
9 Largely based on git's implementation
10 */
11
12 #include <Python.h>
13
14 static const char b85chars[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
15 "abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";
16 static char b85dec[256];
17
18 static void
19 b85prep(void)
20 {
21 int i;
22
23 memset(b85dec, 0, sizeof(b85dec));
24 for (i = 0; i < sizeof(b85chars); i++)
25 b85dec[(int)(b85chars[i])] = i + 1;
26 }
27
28 static PyObject *
29 b85encode(PyObject *self, PyObject *args)
30 {
31 const unsigned char *text;
32 PyObject *out;
33 char *dst;
34 int len, olen, i;
35 unsigned int acc, val, ch;
36
37 if (!PyArg_ParseTuple(args, "s#", &text, &len))
38 return NULL;
39
40 olen = (len + 3) / 4 * 5;
41 if (!(out = PyString_FromStringAndSize(NULL, olen)))
42 return NULL;
43
44 dst = PyString_AS_STRING(out);
45
46 while (len)
47 {
48 acc = 0;
49 for (i = 24; i >= 0; i -= 8) {
50 ch = *text++;
51 acc |= ch << i;
52 if (--len == 0)
53 break;
54 }
55 for (i = 4; i >= 0; i--) {
56 val = acc % 85;
57 acc /= 85;
58 dst[i] = b85chars[val];
59 }
60 dst += 5;
61 }
62
63 return out;
64 }
65
66 static PyObject *
67 b85decode(PyObject *self, PyObject *args)
68 {
69 PyObject *out;
70 const char *text;
71 char *dst;
72 int len, i, j, olen, c;
73 unsigned int acc;
74
75 if (!PyArg_ParseTuple(args, "s#", &text, &len))
76 return NULL;
77
78 olen = (len + 4) / 5 * 4;
79 if (!(out = PyString_FromStringAndSize(NULL, olen)))
80 return NULL;
81
82 dst = PyString_AS_STRING(out);
83
84 for (i = 1; len; i++)
85 {
86 acc = 0;
87 for (j = 0; j < 4 && --len; j++)
88 {
89 c = b85dec[(int)*text++] - 1;
90 if (c < 0)
91 return PyErr_Format(PyExc_ValueError, "Bad base85 character at position %d", i);
92 acc = acc * 85 + c;
93 }
94 if (len--)
95 {
96 c = b85dec[(int)*text++] - 1;
97 if (c < 0)
98 return PyErr_Format(PyExc_ValueError, "Bad base85 character at position %d", i);
99 }
100 else
101 c = 0;
102 /* overflow detection: 0xffffffff == "|NsC0",
103 * "|NsC" == 0x03030303 */
104 if (acc > 0x03030303 || (acc *= 85) > 0xffffffff - c)
105 return PyErr_Format(PyExc_ValueError, "Bad base85 sequence at position %d", i);
106
107 acc += c;
108
109 for (j = 0; j < 4; j++)
110 {
111 acc = (acc << 8) | (acc >> 24);
112 *dst++ = (char)acc;
113 }
114 }
115
116 return out;
117 }
118
119 static char base85_doc[] = "Base85 Data Encoding";
120
121 static PyMethodDef methods[] = {
122 {"b85encode", b85encode, METH_VARARGS, "encode text in base85\n"},
123 {"b85decode", b85decode, METH_VARARGS, "decode base85 text\n"},
124 {NULL, NULL}
125 };
126
127 PyMODINIT_FUNC initbase85(void)
128 {
129 Py_InitModule3("base85", methods, base85_doc);
130
131 b85prep();
132 }