Mercurial > hg
comparison mercurial/base85.c @ 3283:1f2c3983a6c5
Add a base85 codec
author | Brendan Cully <brendan@kublai.com> |
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date | Fri, 06 Oct 2006 13:01:54 -0700 |
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children | e93c926e069e |
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3279:4b2d3c8a6195 | 3283:1f2c3983a6c5 |
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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 } |