core: Add code to read/write "varints"

Adapted from Google protobufs.  For several cases, we want to support
e.g. file sizes up to guint64, but paying the cost of 8 bytes for each
number is too high.

This will be used for static deltas and sizes metadata.

tests/test-varint.c

@@ -0,0 +1,69 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2013 Colin Walters <walters@verbum.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include "config.h"
+
+#include "libgsystem.h"
+
+#include "ostree-varint.h"
+
+static void
+check_one_roundtrip (guint64    val)
+{
+  GString *buf = g_string_new (NULL);
+  guint64 newval;
+  gsize bytes_read;
+
+  _ostree_write_varuint64 (buf, val);
+  if (g_test_verbose ())
+    {
+      gs_unref_variant GVariant *v = g_variant_new_from_data (G_VARIANT_TYPE ("ay"), buf->str, buf->len, TRUE, NULL, NULL);
+      gs_free char *data = g_variant_print (v, FALSE);
+      g_test_message ("%" G_GUINT64_FORMAT " -> %s", val, data);
+    }
+  newval = _ostree_read_varuint64 ((guint8*)buf->str, buf->len, &bytes_read);
+  g_assert_cmpint (bytes_read, <=, 10);
+  g_assert_cmpint (val, ==, newval);
+}
+
+static void
+test_roundtrips (void)
+{
+  const guint64 test_inputs[] = { 0, 1, 0x6F, 0xA0, 0xFF, 0xF0F0, 0xCAFE,
+                                  0xCAFEBABE, G_MAXUINT64, G_MAXUINT64-1,
+                                  G_MAXUINT64 / 2};
+  guint i;
+
+  for (i = 0; i < G_N_ELEMENTS (test_inputs); i++)
+    check_one_roundtrip (test_inputs[i]);
+}
+
+int
+main (int argc, char **argv)
+{
+
+  g_setenv ("GIO_USE_VFS", "local", TRUE);
+
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/ostree/varint", test_roundtrips);
+
+  return g_test_run ();
+}