Verification issue using the Jessie plug-in and Frama-C -


i'm new frama-c , want learn acsl syntax properly. have dummy example , jessie plug-in cannot verify line nr 9 , 12. missing something? function verified (equal) check if 2 arrays (a , b) have same values or not @ each index:

/*@      requires \valid_range(a,0,n-1);      requires \valid_range(b,0,n-1);      requires n >= 0;      requires >= 0 && <= n;      assigns i;      behavior all_equal:          assumes == n;          ensures \result == 1;      behavior some_not_equal:         assumes != n;         ensures \result == 0; */ int equal(int a[], int n, int b[], int i) {   /*@      loop invariant 0 <= <= n;     loop assigns i;     loop variant n-i;   */     (i = 0; < n; i++) {     if (a[i] != b[i])       return 0;   }   return 1; }

there couple of incorrect things here:

behavior all_equal:      assumes == n;      ensures \result == 1;  behavior some_not_equal:     assumes != n;     ensures \result == 0;

in assumes clause, variables evaluated in pre-state of function. meaning if have 2 equal arrays of size n, , assuming i 0 (which not be, see next explanation), i == n fail except when array of size 0

another thing: seem using i variable loop control, setting 0 @ start of loop, in annotations i, in pre-state of program, between 0 , n. in conjunction said 1 of reasons why jessie isn't able prove this.

finally, main reason cannot prove because missing essential loop invariant, 1 guarantees both arrays, array indexes previous current iteration, equal:

loop invariant loop invariant \forall integer k; 0 <= k < ==> a[k] == b[k];

with invariant can specify behaviors better. correct solution problem be:

/*@      requires \valid_range(a,0,n-1);      requires \valid_range(b,0,n-1);      requires n >= 0;      behavior all_equal:          assumes \forall integer k; 0 <= k < n ==> a[k] == b[k];          ensures \result == 1;      behavior some_not_equal:         assumes \exists integer k; 0 <= k < n  && a[k] != b[k];         ensures \result == 0; */ int equal(int a[], int n, int b[]) {   int = 0;   /*@      loop invariant 0 <= <= n;     loop invariant \forall integer k; 0 <= k < ==> a[k] == b[k];     loop assigns i;     loop variant n-i;   */     (i = 0; < n; i++) {     if (a[i] != b[i])       return 0;   }   return 1; }

Comments

Post a Comment

Popular posts from this blog

Why does Ruby on Rails generate add a blank line to the end of a file? -

running rails generate controller foo home results in: class foocontroller < application controller def home end end (there's nothing on line in actual file, blank line) is there purpose blank line? it's common use newline indicate end of line, last line. many editors (like vi, use) add in newline silently. consensus text files (especially in unix world) should end in newline, , there have been problems historically if wasn't present. why should text files end newline? the tool used count lines in file "wc" counts newlines in file, without trailing newline show 3 instead of 4. it improves readability of templates used in generator. consider: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/rails/controller/templates/controller.rb to remove trailing newline, template have last line of: end<% end -%> instead of: end <% end -%> that seems less readable me. the discussion below refers
Read more

keyboard - Smiles and long press feature in Android -

i've created android keyboard. how add features inserting smilies, , using long keypresses display symbols? to create long-press behavior allows select several options pop-up menu, follow guide (specifically pop-up menu section): http://developer.android.com/guide/topics/ui/menus.html smileys (also known emoticons) combination of keys, understood programs , parsed same way. have do, when clicks smiley face on keyboard, simulate pressing of key combination matching emoticon. example, when clicks smiley, should simulate key presses ':' , ')' :). here's list of emoticons: http://en.wikipedia.org/wiki/list_of_emoticons
Read more

node.js - Bad Request - node js ajax post -

i'm using express 3.0 , node v0.11.0. have button submits form , i'm using ajax post data json object node server. client code is: $('#contact').submit(function(e) { console.log('submit called'); var formdata = json.stringify($('form').serializeobject()); console.log(formdata); $.ajax({ url: "http://localhost:3000/savedata/", type: "post", datatype: 'json', data: {objectdata: formdata}, contenttype: "application/json", complete: function() { console.log('process complete'); }, success: function(data) { console.log('process sucess'); }, error: function() { console.log('process error'); }, }); return false; }); then on server: var express = require('express'); var app = express(); app.set('views', __dirname + '/views'); app.set('view engine', 'jade'); app.use(express.bodyparser());
Read more