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IDProjectCategoryView StatusDate SubmittedLast Update
0000365Frama-CDocumentation > manualspublic2010-01-04 17:522016-06-21 14:20
Reporterdwheeler 
Assigned Tocmarche 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionfixed 
Product VersionFrama-C Beryllium-20090902 
Target VersionFixed in VersionFrama-C Carbon-20101201-beta1 
Summary0000365: Jessie tutorial binary_search examples fail with Why 2.23 - loop variant must be added
DescriptionThe 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)
TagsNo tags attached.
Attached Files

-Relationships
related to 0000079assignedvirgile Better support of //@ style 
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-Notes
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+Notes

-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
+Issue History