midx: teach nth_bitmapped_pack() about incremental MIDXs

In a similar fashion as in previous commits, teach the function
`nth_bitmapped_pack()` about incremental MIDXs by translating the given
`pack_int_id` from the concatenated lexical order to a MIDX-local
lexical position.

When accessing the containing MIDX's array of packs, use the local pack
ID. Likewise, when reading the 'BTMP' chunk, use the MIDX-local offset
when accessing the data within that chunk.

(Note that the both the call to prepare_midx_pack() and the assignment
of bp->pack_int_id both care about the global pack_int_id, so avoid
shadowing the given 'pack_int_id' parameter).

Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

midx.c

@@ -311,17 +311,19 @@ int prepare_midx_pack(struct repository *r, struct multi_pack_index *m,
 int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
 		       struct bitmapped_pack *bp, uint32_t pack_int_id)
 {
+	uint32_t local_pack_int_id = midx_for_pack(&m, pack_int_id);
+
 	if (!m->chunk_bitmapped_packs)
 		return error(_("MIDX does not contain the BTMP chunk"));
 
 	if (prepare_midx_pack(r, m, pack_int_id))
 		return error(_("could not load bitmapped pack %"PRIu32), pack_int_id);
 
-	bp->p = m->packs[pack_int_id];
+	bp->p = m->packs[local_pack_int_id];
 	bp->bitmap_pos = get_be32((char *)m->chunk_bitmapped_packs +
-				  MIDX_CHUNK_BITMAPPED_PACKS_WIDTH * pack_int_id);
+				  MIDX_CHUNK_BITMAPPED_PACKS_WIDTH * local_pack_int_id);
 	bp->bitmap_nr = get_be32((char *)m->chunk_bitmapped_packs +
-				 MIDX_CHUNK_BITMAPPED_PACKS_WIDTH * pack_int_id +
+				 MIDX_CHUNK_BITMAPPED_PACKS_WIDTH * local_pack_int_id +
 				 sizeof(uint32_t));
 	bp->pack_int_id = pack_int_id;