[PATCH 03 of 15] util: implement varint functions

[Boris Feld]

# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1474779566 25200
#      Sat Sep 24 21:59:26 2016 -0700
# Node ID b80a8e39ac9bf984c25a666bd7f6c47d876d26af
# Parent  f6baa2844ea380da1a63832a35b1b83007c181a3
# EXP-Topic b2-stream
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r b80a8e39ac9b
util: implement varint functions

This will be useful in an incoming version-2 of the stream format.

diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -3874,3 +3874,36 @@ def readexactly(stream, n):
                            " (got %d bytes, expected %d)")
                           % (len(s), n))
     return s
+
+def uvarintencode(value):
+    """Encode an unsigned integer value to a varint.
+
+    A varint is a variable length integer of 1 or more bytes. Each byte
+    except the last has the most significant bit set. The lower 7 bits of
+    each byte store the 2's complement representation, least significant group
+    first.
+    """
+    bits = value & 0x7f
+    value >>= 7
+    bytes = []
+    while value:
+        bytes.append(pycompat.bytechr(0x80 | bits))
+        bits = value & 0x7f
+        value >>= 7
+    bytes.append(pycompat.bytechr(bits))
+
+    return ''.join(bytes)
+
+def uvarintdecodestream(fh):
+    """Decode an unsigned variable length integer from a stream.
+
+    The passed argument is anything that has a ``.read(N)`` method.
+    """
+    result = 0
+    shift = 0
+    while True:
+        byte = ord(readexactly(fh, 1))
+        result |= ((byte & 0x7f) << shift)
+        if not (byte & 0x80):
+            return result
+        shift += 7