[PATCH 06 of 10 V2] revlog: add a native implementation of issnapshot

[Boris Feld]

# HG changeset patch
# User Boris Feld <boris.feld at octobus.net>
# Date 1545040633 -3600
#      Mon Dec 17 10:57:13 2018 +0100
# Node ID d15f3f46ca1e52f06d5b8f3f77c5e2e02912aaa9
# Parent  4067f496c37ec6d10860504186917bb6be83db46
# EXP-Topic sparse-revlog
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r d15f3f46ca1e
revlog: add a native implementation of issnapshot

This will be used in the next changesets

diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -986,6 +986,34 @@ static inline int index_baserev(indexObj
 	}
 }
 
+static int index_issnapshotrev(indexObject *self, Py_ssize_t rev)
+{
+	int ps[2];
+	Py_ssize_t base;
+	if (rev == -1) {
+		return 1;
+	}
+	base = (Py_ssize_t)index_baserev(self, rev);
+	if (base == rev) {
+		base = -1;
+	}
+	if (base == -2) {
+		assert(PyErr_Occurred());
+		return -1;
+	}
+	if (base == -1) {
+		return 1;
+	}
+	if (index_get_parents(self, rev, ps, (int)rev) < 0) {
+		assert(PyErr_Occurred());
+		return -1;
+	};
+	if (base == ps[0] || base == ps[1]) {
+		return 0;
+	}
+	return index_issnapshotrev(self, base);
+}
+
 static PyObject *index_deltachain(indexObject *self, PyObject *args)
 {
 	int rev, generaldelta;