view mercurial/cext/base85.c @ 46184:cb8b2ee89a5d

copies: stop attempt to avoid extra dict copies around branching

In the python code, we attempt to avoid unnecessary dict copies when gathering
copy information. However that logic is wobbly and I keep running into case
where independent branches affects each others.

With the current code we can't ensure we are the only "user" of dict when
dealing with merge.

This caused havoc in the next series on tests I am about to introduce.

So for now I am disabling the faulty optimisation. I believe we will need a
dedicated overlay to deal with the "copy on write logic" to have something
correct. I am also hoping to find time to build dedicated test case for this
category of problem instead of relying on side effect in other tests. However
for now I am focussing on another issue.

Differential Revision: https://phab.mercurial-scm.org/D9608

/*
 base85 codec

 Copyright 2006 Brendan Cully <[e-mail]>

 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
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>

#include "util.h"

static const char b85chars[] =
    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";
static char b85dec[256];

static void b85prep(void)
{
	unsigned 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;
	Py_ssize_t len, olen, i;
	unsigned int acc, val, ch;
	int pad = 0;

	if (!PyArg_ParseTuple(args, PY23("s#|i", "y#|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 = PyBytes_FromStringAndSize(NULL, olen + 3))) {
		return NULL;
	}

	dst = PyBytes_AsString(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) {
		_PyBytes_Resize(&out, olen);
	}

	return out;
}

static PyObject *b85decode(PyObject *self, PyObject *args)
{
	PyObject *out = NULL;
	const char *text;
	char *dst;
	Py_ssize_t len, i, j, olen, cap;
	int c;
	unsigned int acc;

	if (!PyArg_ParseTuple(args, PY23("s#", "y#"), &text, &len)) {
		return NULL;
	}

	olen = len / 5 * 4;
	i = len % 5;
	if (i) {
		olen += i - 1;
	}
	if (!(out = PyBytes_FromStringAndSize(NULL, olen))) {
		return NULL;
	}

	dst = PyBytes_AsString(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) {
				PyErr_Format(
				    PyExc_ValueError,
				    "bad base85 character at position %d",
				    (int)i);
				goto bail;
			}
			acc = acc * 85 + c;
		}
		if (i++ < len) {
			c = b85dec[(int)*text++] - 1;
			if (c < 0) {
				PyErr_Format(
				    PyExc_ValueError,
				    "bad base85 character at position %d",
				    (int)i);
				goto bail;
			}
			/* overflow detection: 0xffffffff == "|NsC0",
			 * "|NsC" == 0x03030303 */
			if (acc > 0x03030303 || (acc *= 85) > 0xffffffff - c) {
				PyErr_Format(
				    PyExc_ValueError,
				    "bad base85 sequence at position %d",
				    (int)i);
				goto bail;
			}
			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;
bail:
	Py_XDECREF(out);
	return NULL;
}

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},
};

static const int version = 1;

#ifdef IS_PY3K
static struct PyModuleDef base85_module = {
    PyModuleDef_HEAD_INIT, "base85", base85_doc, -1, methods,
};

PyMODINIT_FUNC PyInit_base85(void)
{
	PyObject *m;
	b85prep();

	m = PyModule_Create(&base85_module);
	PyModule_AddIntConstant(m, "version", version);
	return m;
}
#else
PyMODINIT_FUNC initbase85(void)
{
	PyObject *m;
	m = Py_InitModule3("base85", methods, base85_doc);

	b85prep();
	PyModule_AddIntConstant(m, "version", version);
}
#endif