0000365: Jessie tutorial binary_search examples fail with Why 2.23 - loop variant must be added

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0000365

Frama-C

Documentation > manuals

public

2010-01-04 17:52

2016-06-21 14:20

Reporter

dwheeler

Assigned To

cmarche

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

Frama-C Beryllium-20090902

Target Version

Fixed in Version

Frama-C Carbon-20101201-beta1

Summary

0000365: Jessie tutorial binary_search examples fail with Why 2.23 - loop variant must be added

Description

The Jessie tutorial in: http://frama-c.cea.fr/jessie_tutorial_index.html sections 2.1 and 2.2 include binary_search examples. If "Why" is upgraded to Why 2.23, these no longer work, because there is no loop variant provided. The single loop invariant must be changed to be: /*@ loop invariant 0 <= l && u <= n-1; loop variant u-l; */ In addition, explain loop variants, since they are absolutely necessary to use Why 2.23. Also, please note in the documentation that this will NOT work: //@ loop invariant 0 <= l && u <= n-1; //@ loop variant u-l; Basically, make it clear that you're not allowed to have "//@" in succession, especially since doing this produces a mysterious and misleading error message. See bug 79. The example of 2.2 should end up looking like this (the lemma is optional): /*@ lemma mean: \forall integer x, y; x <= y ==> x <= (x+y)/2 <= y; */ //@ requires n >= 0 && \valid_range(t,0,n-1); int binary_search(int* t, int n, int v) { int l = 0, u = n-1, p = -1; /*@ loop invariant 0 <= l && u <= n-1; @ loop variant u-l; */ while (l <= u ) { int m = l + (u - l) / 2; // NOTE this is changed for bounded calculation if (t[m] < v) l = m + 1; else if (t[m] > v) u = m - 1; else { p = m; break; } } return p; }

Additional Information

Fixed in Frama-C SVN (doc/jessie)

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related to

0000079

assigned

virgile

Better support of //@ style

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Issue History
Date Modified	Username	Field	Change
2010-01-04 17:52	dwheeler	New Issue
2010-01-05 08:40	signoles	Status	new => assigned
2010-01-05 08:40	signoles	Assigned To	=> cmarche
2010-01-05 08:41	signoles	Relationship added	related to 0000079
2010-02-01 13:01	cmarche	Status	assigned => resolved
2010-02-01 13:01	cmarche	Resolution	open => fixed
2010-02-01 13:01	cmarche	Additional Information Updated
2010-12-10 15:45	signoles	Fixed in Version	=> Frama-C Carbon-20101201-beta1
2010-12-17 19:37	signoles	Status	resolved => closed
2016-06-21 14:11	signoles	Category	Documentation => Documentation > ACSL
2016-06-21 14:20	signoles	Category	Documentation > ACSL => Documentation > manuals