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