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
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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? 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 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 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 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 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 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 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 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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