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In DCE 1.1, the time_low value is defined as an unsigned 32-bit

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integer.  Presently, our implementation employs an approach that
converts the value to int64_t, then back to int, unfortunately,
this approach can be problematic when the the difference between
the two time_low is larger than 0x7fffffff, as the value is then
truncated to int.

To quote the test case from the original PR, the following is
true with the current implementation:

865e1a56-b9d9-11d9-ba27-0003476f2e88 < 062ac45c-b9d9-11d9-ba27-0003476f2e88

However, according to the DCE specification, the expected result
should be:

865e1a56-b9d9-11d9-ba27-0003476f2e88 > 062ac45c-b9d9-11d9-ba27-0003476f2e88

This commit adds a new intermediate variable which uses int64_t
to store the result of subtraction between the two time_low values,
which would not introduce different semantic of the MSB found in
time_low value.

PR:		83107
Submitted by:	Steve Sears <sjs at acm dot org>
MFC After:	1 month
This commit is contained in:
Xin LI 2006-08-03 03:34:36 +00:00
parent 3e6a93dd95
commit da4ab3aa26
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=160938
1 changed files with 15 additions and 5 deletions
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20
lib/libc/uuid/uuid_compare.c
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@ -41,7 +41,8 @@
int32_t
uuid_compare(const uuid_t *a, const uuid_t *b, uint32_t *status)
{
int res;
int res;
int64_t res64;
if (status != NULL)
*status = uuid_s_ok;
@ -54,10 +55,19 @@ uuid_compare(const uuid_t *a, const uuid_t *b, uint32_t *status)
if (b == NULL)
return ((uuid_is_nil(a, NULL)) ? 0 : 1);
/* We have to compare the hard way. */
res = (int)((int64_t)a->time_low - (int64_t)b->time_low);
if (res)
return ((res < 0) ? -1 : 1);
/*
* We have to compare the hard way.
*
* Note that time_low is defined as unsigned 32-bit
* integer, therefore, with a significantly large
* a->time_low and a small b->time_low, we will end
* up with a value which is larger than 0x7fffffff
* which is negative if casted to signed 32-bit
* integer.
*/
res64 = (int64_t)a->time_low - (int64_t)b->time_low;
if (res64)
return ((res64 < 0) ? -1 : 1);
res = (int)a->time_mid - (int)b->time_mid;
if (res)
return ((res < 0) ? -1 : 1);