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