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By Dave, on April 23rd, 2018
The leftPad(string,int) function simply pads a string up to a given size by inserted spaces at the beginning. For example, leftPad(“hello”,8) produces ” hello”. This little function shot to fame in 2016 when a developer pulled all his modules from NPM, of which one provided the leftPad() functionality. There were two basic issues causing . . . → Read More: Verifying leftPad() in Whiley
By Dave, on September 1st, 2016
Recently, as part of our Programming Languages Reading group, we looked at the paper “Contracts in Practice” by Estler et al., (see here for a copy). This is quite an interesting paper and the authors perform an empirical investigation as to how contracts are used by programmers in practice. They dig out some data . . . → Read More: Program Specification in Practice?
By Dave, on November 12th, 2015
In this post, we’re going to consider representing the classic C string in Whiley. This turns out to be useful as we can then try to verify properties about functions which operate on C strings (e.g. strlen(), strcpy(), etc). If you’re not familiar with C strings, then the main points are:
Roughly speaking, C . . . → Read More: Encoding C Strings in Whiley
By Dave, on October 6th, 2015
A couple of weeks back, I gave a presentation to the Wellington Java User Group. The talk provides a useful introduction to verifying software in Whiley, and shows a bunch of interesting examples. Anyway, you can see the presentation here:
Wellington Java User Group Presentation from John Hurst on Vimeo.
. . . → Read More: Verifying Software with Whiley
By Dave, on September 22nd, 2015
We’ve started using Whiley again in my second year course Formal Foundations of Programming. The aim of this course is to introduce students into a range of techniques related to software correctness. So far, we’ve looked at some static analysis and model checking tools.
Anyway, last week I gave an introductory lecture on writing . . . → Read More: Introductory Lecture on Verification in Whiley
By Dave, on December 9th, 2014
Recently, I was listening to the latest edition of the Illegal Argument podcast, and it turns out they were discussing Whiley! (about 103:16 minutes in). The discussion was about how verification interacts with data from an untrusted source (e.g. from a database, network connection, etc). In particular, whether or not we can safely feed . . . → Read More: Verification with Data from Untrusted Sources
By Dave, on July 10th, 2014
Proving that a loop always terminates is a common requirement when verifying software. The usual approach to doing this is to provide a loop variant function. This is typically an integer expression which decreases on every iteration of the loop. Consider the following loop:
function contains([int] items, int item) => bool: int i = . . . → Read More: Loop Variant Relations
By Dave, on June 20th, 2014
Verification tools often support the use of ghost variables to help in the verification process. A ghost variable is not needed for the program to execute, and will not be compiled into object code. Typically, they are declared with a ghost modifier or similar, but are otherwise identical to normal program variables (i.e. they . . . → Read More: Understanding Ghost Variables in Software Verification
By Dave, on May 15th, 2014
Recently, I encountered what I thought was a bug in the Whiley Compiler. The issue related to the current treatment of do/while loops and loop invariants. Having now spent a fair bit of time researching the issue, the answer is not so clear.
The problem manifested itself when I tried to verify the following . . . → Read More: Loop Invariants and Do/While Statements
By Dave, on May 2nd, 2014
In this article, I’ll look at some interesting issues relating to the use of break statements within loops, and how this affects the idea of a loop invariant. For some general background on writing loop invariants in Whiley, see my previous post. To recap the main points, here’s a simple function which requires a . . . → Read More: Loop invariants and Break Statements
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