Re: [PATCH v8 03/14] commit-graph: add format document

Derrick Stolee [off-list ref] writes:

On 4/11/2018 4:58 PM, Jakub Narebski wrote:

quoted

Derrick Stolee [off-list ref] writes:

quoted

+CHUNK DATA:
+
+  OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
+      The ith entry, F[i], stores the number of OIDs with first
+      byte at most i. Thus F[255] stores the total
+      number of commits (N).
+
+  OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
+      The OIDs for all commits in the graph, sorted in ascending order.
+
+  Commit Data (ID: {'C', 'G', 'E', 'T' }) (N * (H + 16) bytes)

I think it is a typo, and it should be CDAT, not CGET
(CDAT seem to me to stand for Commit DATa):

   +  Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)

This is what you use in actual implementation, in PATCH v8 06/14

DS> +#define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
DS> +#define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
DS> +#define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
DS> +#define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
DS> +#define GRAPH_CHUNKID_LARGEEDGES 0x45444745 /* "EDGE" */

Documentation bugs are hard to diagnose. Thanks for finding this. I
double checked that the hex int "0x43444154" matches "CDAT".

Another possible way of checking the correctness would be to run
`hexdump -C` or equivalent on generated commit-graph file.  File and
chunk headers should be visible in its output.