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hex: default to the_hash_algo on zero algorithm value 

There are numerous places in the codebase where we assume we can
initialize data by zeroing all its bytes.  However, when we do that with
a struct object_id, it leaves the structure with a zero value for the
algorithm, which is invalid.

We could forbid this pattern and require that all struct object_id
instances be initialized using oidclr, but this seems burdensome and
it's unnatural to most C programmers.  Instead, if the algorithm is
zero, assume we wanted to use the default hash algorithm instead.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
brian m. carlson 2021-04-26 01:03:00 +00:00 committed by Junio C Hamano
parent 71b7672b67
commit b8505ecbf2
1 changed files with 7 additions and 0 deletions
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7
hex.c
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@ -124,6 +124,13 @@ char *hash_to_hex_algop_r(char *buffer, const unsigned char *hash,
char *buf = buffer;
int i;
/*
* Our struct object_id has been memset to 0, so default to printing
* using the default hash.
*/
if (algop == &hash_algos[0])
algop = the_hash_algo;
for (i = 0; i < algop->rawsz; i++) {
unsigned int val = *hash++;
*buf++ = hex[val >> 4];