Nicolas Pitre <nico@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> ---
> 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].
> +/*
> + * Encode an object SHA1 reference with either an object index into the
> + * pack SHA1 table incremented by 1, or the literal SHA1 value prefixed
> + * with a zero byte if the needed SHA1 is not available in the table.
> + */
> +static struct pack_idx_entry *all_objs;
> +static unsigned all_objs_nr;
> +static unsigned char *add_sha1_ref(unsigned char *dst, const unsigned char *sha1)
> +{
> + unsigned lo = 0, hi = all_objs_nr;
> +
> + do {
> + unsigned mi = (lo + hi) / 2;
> + int cmp = hashcmp(all_objs[mi].sha1, sha1);
> +
> + if (cmp == 0)
> + return add_number(dst, mi + 1);
> + if (cmp > 0)
> + hi = mi;
> + else
> + lo = mi+1;
> + } while (lo < hi);
> +
> + *dst++ = 0;
> + hashcpy(dst, sha1);
> + return dst + 20;
> +}
> +
> static struct pack_idx_entry *get_packed_object_list(struct packed_git *p)
> {
> unsigned i, nr_objects = p->num_objects;
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