Re: [PATCH 08/23] pack v4: basic references encoding

> Nicolas Pitre <nico@fluxnic.net> writes:
> 
> > Add variable length number encoding.  Let's apply the same encoding
> > currently used for the offset to base of OBJ_OFS_DELTA objects which
> > is the most efficient way to do this, and apply it to everything with
> > pack version 4.
> >
> > Also add SHA1 reference encoding.  This one is either an index into a
> > SHA1 table encoded using the variable length number encoding, or the
> > literal 20 bytes SHA1 prefixed with a 0.
> >
> > The index 0 discriminates between an actual index value or the literal
> > SHA1.  Therefore when the index is used its value must be increased by 1.
> >
> > Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
> > ---
> >  packv4-create.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >
> > diff --git a/packv4-create.c b/packv4-create.c
> > index 012129b..bf33d15 100644
> > --- a/packv4-create.c
> > +++ b/packv4-create.c
> > @@ -245,6 +245,50 @@ static void dict_dump(void)
> >  	dump_dict_table(tree_path_table);
> >  }
> >  
> > +/*
> > + * Encode a numerical value with variable length into the destination buffer
> > + */
> > +static unsigned char *add_number(unsigned char *dst, uint64_t value)
> > +{
> > +	unsigned char buf[20];
> > +	unsigned pos = sizeof(buf) - 1;
> > +	buf[pos] = value & 127;
> > +	while (value >>= 7)
> > +		buf[--pos] = 128 | (--value & 127);
> > +	do {
> > +		*dst++ = buf[pos++];
> > +	} while (pos < sizeof(buf));
> > +	return dst;
> > +}
> 
> This may want to reuse (or enhance-then-reuse) varint.[ch].