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 }