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/*
base85 codec
Copyright 2006 Brendan Cully <brendan@kublai.com>
This software may be used and distributed according to the terms of
the GNU General Public License, incorporated herein by reference.
Largely based on git's implementation
*/
#include <Python.h>
static const char b85chars[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";
static char b85dec[256];
static void
b85prep(void)
{
int i;
memset(b85dec, 0, sizeof(b85dec));
for (i = 0; i < sizeof(b85chars); i++)
b85dec[(int)(b85chars[i])] = i + 1;
}
static PyObject *
b85encode(PyObject *self, PyObject *args)
{
const unsigned char *text;
PyObject *out;
char *dst;
int len, olen, i;
unsigned int acc, val, ch;
int pad = 0;
if (!PyArg_ParseTuple(args, "s#|i", &text, &len, &pad))
return NULL;
if (pad)
olen = ((len + 3) / 4 * 5) - 3;
else {
olen = len % 4;
if (olen)
olen++;
olen += len / 4 * 5;
}
if (!(out = PyString_FromStringAndSize(NULL, olen + 3)))
return NULL;
dst = PyString_AS_STRING(out);
while (len) {
acc = 0;
for (i = 24; i >= 0; i -= 8) {
ch = *text++;
acc |= ch << i;
if (--len == 0)
break;
}
for (i = 4; i >= 0; i--) {
val = acc % 85;
acc /= 85;
dst[i] = b85chars[val];
}
dst += 5;
}
if (!pad)
_PyString_Resize(&out, olen);
return out;
}
static PyObject *
b85decode(PyObject *self, PyObject *args)
{
PyObject *out;
const char *text;
char *dst;
int len, i, j, olen, c, cap;
unsigned int acc;
if (!PyArg_ParseTuple(args, "s#", &text, &len))
return NULL;
olen = len / 5 * 4;
i = len % 5;
if (i)
olen += i - 1;
if (!(out = PyString_FromStringAndSize(NULL, olen)))
return NULL;
dst = PyString_AS_STRING(out);
i = 0;
while (i < len)
{
acc = 0;
cap = len - i - 1;
if (cap > 4)
cap = 4;
for (j = 0; j < cap; i++, j++)
{
c = b85dec[(int)*text++] - 1;
if (c < 0)
return PyErr_Format(PyExc_ValueError, "Bad base85 character at position %d", i);
acc = acc * 85 + c;
}
if (i++ < len)
{
c = b85dec[(int)*text++] - 1;
if (c < 0)
return PyErr_Format(PyExc_ValueError, "Bad base85 character at position %d", i);
/* overflow detection: 0xffffffff == "|NsC0",
* "|NsC" == 0x03030303 */
if (acc > 0x03030303 || (acc *= 85) > 0xffffffff - c)
return PyErr_Format(PyExc_ValueError, "Bad base85 sequence at position %d", i);
acc += c;
}
cap = olen < 4 ? olen : 4;
olen -= cap;
for (j = 0; j < 4 - cap; j++)
acc *= 85;
if (cap && cap < 4)
acc += 0xffffff >> (cap - 1) * 8;
for (j = 0; j < cap; j++)
{
acc = (acc << 8) | (acc >> 24);
*dst++ = acc;
}
}
return out;
}
static char base85_doc[] = "Base85 Data Encoding";
static PyMethodDef methods[] = {
{"b85encode", b85encode, METH_VARARGS,
"Encode text in base85.\n\n"
"If the second parameter is true, pad the result to a multiple of "
"five characters.\n"},
{"b85decode", b85decode, METH_VARARGS, "Decode base85 text.\n"},
{NULL, NULL}
};
PyMODINIT_FUNC initbase85(void)
{
Py_InitModule3("base85", methods, base85_doc);
b85prep();
}
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