0005222: Hashtbl.hash is not compatible with (=) - MantisBT

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ID

Project

Category

View Status

Date Submitted

Last Update

0005222

OCaml

OCaml general

public

2011-02-09 13:51

2012-09-25 20:06

Reporter

Pascal Cuoq

Assigned To

xleroy

Priority

normal

Severity

major

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS

OS Version

Product Version

3.12.0

Target Version

Fixed in Version

Summary

0005222: Hashtbl.hash is not compatible with (=)

Description

According to http://caml.inria.fr/pub/docs/manual-ocaml/libref/Hashtbl.html [^] :

Hashtbl.hash x associates a positive integer to any value of any type. It is guaranteed that if x = y or Pervasives.compare x y = 0, then hash x = hash y.

But:

Objective Caml version 3.12.0

# Hashtbl.hash (+0.) ;;
- : int = 0
# Hashtbl.hash (-0.) ;;
- : int = 128
# (+0.) = (-0.) ;;
- : bool = true
#

Tags

No tags attached.

Relationships

related to

closed

Strengthen the built-in hash function

Notes
(0005838) xleroy (administrator) 2011-03-04 16:30	Well spotted, thanks. Some normalization of the float is in order before hashing its bits.

(0005935) xleroy (administrator) 2011-05-29 12:10	As part of a major overhaul of the generic hash function, fixed the +0.0/-0.0 issue, and also made sure that all NaNs hash to the same value. The code is in SVN trunk and should go into release 3.13.

Issue History
Date Modified	Username	Field	Change
2011-02-09 13:51	Pascal Cuoq	New Issue
2011-03-04 16:26	xleroy	Relationship added	related to 0005225
2011-03-04 16:30	xleroy	Note Added: 0005838
2011-03-04 16:30	xleroy	Assigned To	=> xleroy
2011-03-04 16:30	xleroy	Status	new => confirmed
2011-05-29 12:10	xleroy	Note Added: 0005935
2011-05-29 12:10	xleroy	Status	confirmed => resolved
2011-05-29 12:10	xleroy	Resolution	open => fixed
2012-09-25 20:06	xleroy	Status	resolved => closed

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