[PATCH 02 of 14] util: implement varint functions

[Yuya Nishihara]

On Thu, 18 Jan 2018 12:21:28 +0100, Boris Feld wrote:
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc at gmail.com>
> # Date 1474779566 25200
> #      Sat Sep 24 21:59:26 2016 -0700
> # Node ID 1262be5f656bb0597b59a7dd2139b81922829fae
> # Parent  939c242897c47ede8cda0b0a0149e15b74803402
> # EXP-Topic b2-stream
> # Available At https://bitbucket.org/octobus/mercurial-devel/
> #              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 1262be5f656b
> util: implement varint functions

(I stopped here. This series will need to be reviewed by someone having more
expertise, and I don't think I can finish reviewing today.)

> +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(chr(0x80 | bits))
> +        bits = value & 0x7f
> +        value >>= 7
> +    bytes.append(chr(bits))

Nit: use pycompat.bytechr()

> +    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(fh.read(1))

Need to test EOF?

Alternatively, we could split this function into
 a) read bytes while MSB is set
 b) decode bytes into integer (in reverse order)

> +        result |= ((byte & 0x7f) << shift)
> +        if not (byte & 0x80):
> +            return result
> +        shift += 7