/*

 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();

}