pack-objects: pass length to check_pack_crc() without truncation

On 32 bit systems with large file support, unsigned long is 32-bit
while the two offsets in the subtraction expression (pack-objects has
the exact same expression as in sha1_file.c but not shown in diff) are
in 64-bit. If an in-pack object is larger than 2^32 len/datalen is
truncated and we get a misleading "error: bad packed object CRC for
..." as a result.

Use off_t for len and datalen. check_pack_crc() already accepts this
argument as off_t and can deal with 4+ GB.

Noticed-by: Christoph Michelbach <michelbach94@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -349,7 +349,7 @@ static unsigned long write_reuse_object(struct sha1file *f, struct object_entry
 	struct revindex_entry *revidx;
 	off_t offset;
 	enum object_type type = entry->type;
-	unsigned long datalen;
+	off_t datalen;
 	unsigned char header[10], dheader[10];
 	unsigned hdrlen;
 

sha1_file.c

@@ -2282,7 +2282,7 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 
 		if (do_check_packed_object_crc && p->index_version > 1) {
 			struct revindex_entry *revidx = find_pack_revindex(p, obj_offset);
-			unsigned long len = revidx[1].offset - obj_offset;
+			off_t len = revidx[1].offset - obj_offset;
 			if (check_pack_crc(p, &w_curs, obj_offset, len, revidx->nr)) {
 				const unsigned char *sha1 =
 					nth_packed_object_sha1(p, revidx->nr);