parsers: add fm1readmarker

This lets us do most of the interesting work of parsing obsolete
markers in C, which should provide significant time savings.

Thanks to Martin von Zweigbergk for some cleanups on this code.

mercurial/parsers.c

@@ -2146,6 +2146,127 b' bail:'
 	return NULL;
 }
 
+#define BUMPED_FIX 1
+#define USING_SHA_256 2
+
+static PyObject *readshas(
+	const char *source, unsigned char num, Py_ssize_t hashwidth)
+{
+	int i;
+	PyObject *list = PyTuple_New(num);
+	if (list == NULL) {
+		return NULL;
+	}
+	for (i = 0; i < num; i++) {
+		PyObject *hash = PyString_FromStringAndSize(source, hashwidth);
+		if (hash == NULL) {
+			Py_DECREF(list);
+			return NULL;
+		}
+		PyTuple_SetItem(list, i, hash);
+		source += hashwidth;
+	}
+	return list;
+}
+
+static PyObject *fm1readmarker(PyObject *self, PyObject *args)
+{
+	const char *data;
+	const char *meta;
+	Py_ssize_t datalen, offset;
+
+	uint32_t msize;
+	double mtime;
+	int16_t tz;
+	uint16_t flags;
+	unsigned char nsuccs, nparents, nmetadata;
+	Py_ssize_t hashwidth = 20;
+
+	PyObject *prec = NULL, *parents = NULL, *succs = NULL;
+	PyObject *metadata = NULL, *ret = NULL;
+	int i;
+
+	if (!PyArg_ParseTuple(args, "s#n", &data, &datalen, &offset)) {
+		return NULL;
+	}
+	data += offset;
+
+	msize = getbe32(data);
+	data += 4;
+	mtime = getbefloat64(data);
+	data += 8;
+	tz = getbeint16(data);
+	data += 2;
+	flags = getbeuint16(data);
+	data += 2;
+
+	if (flags & USING_SHA_256) {
+		hashwidth = 32;
+	}
+
+	nsuccs = (unsigned char)(*data++);
+	nparents = (unsigned char)(*data++);
+	nmetadata = (unsigned char)(*data++);
+
+	prec = PyString_FromStringAndSize(data, hashwidth);
+	data += hashwidth;
+	if (prec == NULL) {
+		goto bail;
+	}
+
+	succs = readshas(data, nsuccs, hashwidth);
+	if (succs == NULL) {
+		goto bail;
+	}
+	data += nsuccs * hashwidth;
+
+	if (nparents == 1 || nparents == 2) {
+		parents = readshas(data, nparents, hashwidth);
+		if (parents == NULL) {
+			goto bail;
+		}
+		data += nparents * hashwidth;
+	} else {
+		parents = Py_None;
+	}
+
+	meta = data + (2 * nmetadata);
+	metadata = PyTuple_New(nmetadata);
+	if (metadata == NULL) {
+		goto bail;
+	}
+	for (i = 0; i < nmetadata; i++) {
+		PyObject *tmp, *left = NULL, *right = NULL;
+		Py_ssize_t metasize = (unsigned char)(*data++);
+		left = PyString_FromStringAndSize(meta, metasize);
+		meta += metasize;
+		metasize = (unsigned char)(*data++);
+		right = PyString_FromStringAndSize(meta, metasize);
+		meta += metasize;
+		if (!left || !right) {
+			Py_XDECREF(left);
+			Py_XDECREF(right);
+			goto bail;
+		}
+		tmp = PyTuple_Pack(2, left, right);
+		Py_DECREF(left);
+		Py_DECREF(right);
+		if (!tmp) {
+			goto bail;
+		}
+		PyTuple_SetItem(metadata, i, tmp);
+	}
+	ret = Py_BuildValue("(nOOHO(di)O)", msize, prec, succs, flags,
+			    metadata, mtime, (int)tz * 60, parents);
+bail:
+	Py_XDECREF(prec);
+	Py_XDECREF(succs);
+	Py_XDECREF(metadata);
+	if (parents != Py_None)
+		Py_XDECREF(parents);
+	return ret;
+}
+
 static char parsers_doc[] = "Efficient content parsing.";
 
 PyObject *encodedir(PyObject *self, PyObject *args);
@@ -2161,6 +2282,7 b' static PyMethodDef methods[] = {'
 	{"encodedir", encodedir, METH_VARARGS, "encodedir a path\n"},
 	{"pathencode", pathencode, METH_VARARGS, "fncache-encode a path\n"},
 	{"lowerencode", lowerencode, METH_VARARGS, "lower-encode a path\n"},
+	{"fm1readmarker", fm1readmarker, METH_VARARGS, "parse v1 obsolete marker\n"},
 	{NULL, NULL}
 };