base85.c
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/ mercurial / base85.c
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r3283 | /* | ||
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; | ||||
if (!PyArg_ParseTuple(args, "s#", &text, &len)) | ||||
return NULL; | ||||
olen = (len + 3) / 4 * 5; | ||||
if (!(out = PyString_FromStringAndSize(NULL, olen))) | ||||
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; | ||||
} | ||||
return out; | ||||
} | ||||
static PyObject * | ||||
b85decode(PyObject *self, PyObject *args) | ||||
{ | ||||
PyObject *out; | ||||
const char *text; | ||||
char *dst; | ||||
int len, i, j, olen, c; | ||||
unsigned int acc; | ||||
if (!PyArg_ParseTuple(args, "s#", &text, &len)) | ||||
return NULL; | ||||
olen = (len + 4) / 5 * 4; | ||||
if (!(out = PyString_FromStringAndSize(NULL, olen))) | ||||
return NULL; | ||||
dst = PyString_AS_STRING(out); | ||||
for (i = 1; len; i++) | ||||
{ | ||||
acc = 0; | ||||
for (j = 0; j < 4 && --len; 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 (len--) | ||||
{ | ||||
c = b85dec[(int)*text++] - 1; | ||||
if (c < 0) | ||||
return PyErr_Format(PyExc_ValueError, "Bad base85 character at position %d", i); | ||||
} | ||||
else | ||||
c = 0; | ||||
/* 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; | ||||
for (j = 0; j < 4; j++) | ||||
{ | ||||
acc = (acc << 8) | (acc >> 24); | ||||
*dst++ = (char)acc; | ||||
} | ||||
} | ||||
return out; | ||||
} | ||||
static char base85_doc[] = "Base85 Data Encoding"; | ||||
static PyMethodDef methods[] = { | ||||
{"b85encode", b85encode, METH_VARARGS, "encode text in base85\n"}, | ||||
{"b85decode", b85decode, METH_VARARGS, "decode base85 text\n"}, | ||||
{NULL, NULL} | ||||
}; | ||||
PyMODINIT_FUNC initbase85(void) | ||||
{ | ||||
Py_InitModule3("base85", methods, base85_doc); | ||||
b85prep(); | ||||
} | ||||