0004740: Int32.rem floating point exception - MantisBT

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ID

Project

Category

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Date Submitted

Last Update

0004740

OCaml

OCaml general

public

2009-03-08 09:17

2012-02-23 15:58

Reporter

delorimier

Assigned To

xleroy

Priority

normal

Severity

crash

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS

OS Version

Product Version

3.10.2

Target Version

Fixed in Version

3.11.1+dev

Summary

0004740: Int32.rem floating point exception

Description

(Int32.rem Int32.min_int Int32.minus_one) gives a machine generated floating point exception, and exits the toplevel interpretor.
The expression should return Int32.zero.

My machine is a 32 bit x86.
This bug occurs in version 3.10.2 bytecode and native.
It also occurs in version 3.10.0 bytecode, and I did not try native.

Here's an example:
% ocaml
Objective Caml version 3.10.2

# open Int32;;
# rem min_int minus_one;;
zsh: floating point exception ocaml
%

I couldn't find any other bad Int32.rem cases.

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No tags attached.

Relationships

related to

resolved

Int64.div causes floating point exception

Notes
(0004850) delorimier (reporter) 2009-03-08 21:52	I also get the same error with Int32.div

(0004887) xleroy (administrator) 2009-03-28 19:44	Let's start with division first, since this is where the real problem lies. Dividing min_int by (-1) gives a result (- min_int) which is not representable in two's complement. Some processors (x86) raise a hardware exception in this case, other return min_int, yet others produce unspecified results. Concerning remainder, min_int rem (-1) is perfectly representable since it is 0, but processors like x86 have only one instruction that computes the quotient and the remainder, so the same problems as with division occur. I agree this undefined behavior in OCaml is not nice, therefore I implemented a fix whereas Int32.div Int32.min_int Int32.minus_one = Int32.min_int and Int32.rem Int32.min_int Int32.minus_one = Int32.zero. (Likewise for Int64 and Nativeint.) This behavior is consistent with that of "/" and "mod" at type int. The fix is in the 3.11 bugfix branch and will be in release 3.11.1.

Issue History
Date Modified	Username	Field	Change
2009-03-08 09:17	delorimier	New Issue
2009-03-08 21:52	delorimier	Note Added: 0004850
2009-03-28 16:57	xleroy	Status	new => assigned
2009-03-28 16:57	xleroy	Assigned To	=> xleroy
2009-03-28 19:44	xleroy	Note Added: 0004887
2009-03-28 19:44	xleroy	Status	assigned => resolved
2009-03-28 19:44	xleroy	Resolution	open => fixed
2009-04-02 11:55	xleroy	Fixed in Version	=> 3.11.1+dev
2011-05-29 12:14	xleroy	Status	resolved => closed
2012-02-23 15:58	xleroy	Relationship added	related to 0005513

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