Bug 23040 - GetHashCode for Guids always returns 0
Summary: GetHashCode for Guids always returns 0
Alias: None
Product: Class Libraries
Classification: Mono
Component: System ()
Version: 3.6.0
Hardware: PC Linux
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2014-09-16 07:00 UTC by oliver.klemencic
Modified: 2014-09-17 01:34 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

Testcase (224 bytes, text/plain)
2014-09-16 07:01 UTC, oliver.klemencic
collisions counting demo (769 bytes, text/plain)
2014-09-17 01:34 UTC, oliver.klemencic

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Description oliver.klemencic 2014-09-16 07:00:52 UTC
Under Mono, the GetHashCode method for Guid data types returns always "0". I tested it with 3.3.0 on Windows and Mono 3.6.0 on Linux.

Attached, you find a testcase demonstrating the problem.
Comment 1 oliver.klemencic 2014-09-16 07:01:17 UTC
Created attachment 8074 [details]
Comment 2 Marek Safar 2014-09-16 07:18:11 UTC
GetHashCode does not always return 0 but it does sometime. It needs to encode 128 bits information in 32bits.
Comment 3 oliver.klemencic 2014-09-17 01:33:40 UTC
Ok, looks like I just found some bad Guids. I now tested the number of collisions when using Mono compared to using .NET

For 100.000 Guids Mono had 4 collisions, whereas .NET had 2 (see attached demo). So nothing which is really a problem.
Comment 4 oliver.klemencic 2014-09-17 01:34:03 UTC
Created attachment 8086 [details]
collisions counting demo