This is the followup piece to Monday’s bit puzzle. First off, the spec for this problem wasn’t clear what to return when both arguments are the same. But let’s look at Carlos’s comment about where this code would be used: If you think of a binary number as a sequence of binary tree decisions on the [...]
An important part of effective random testing is providing developers with actionable testcases, and a big part of creating actionable testcases is testcase reduction. Delta debugging, as exemplified by the delta tool, is a good generic reduction technique. However, in many cases, as I discussed the other day here, a domain-specific reducer can do a [...]
My last post outlined some of the possibilities for integer semantics in programming languages, and asked which option was correct. This post contains my answers. Just to be clear: I want practical solutions, but I’m not very interested by historical issues or backwards compatibility with any existing language, and particularly not with C and C++. [...]
Test case reduction is a common problem faced by programmers where some large input (or more generally, some complicated set of circumstances) causes a program to fail, but we wish to know the smallest input (or the simplest circumstances) that causes the same failure. Reduced test cases are important because: Since the bulk of the [...]
We’ve released version 2.1 of Csmith, our random C program generator that is useful for finding bugs in compilers and other tools that process C code. The total number of compiler bugs found and reported due to Csmith is now more than 400. All Csmith users should strongly consider upgrading. New features in this release [...]
The other day I posted about a simple, low-effort way to improve the bug-finding performance of a random tester. We now have a draft paper about this topic, it’s joint work between my group at Utah and Alex Groce’s group at Oregon State. The key claim is: … for realistic systems, randomly excluding some features [...]
Last Spring I had a lucky conversation. I was chatting with Vikram Adve, while visiting the University of Illinois, and we realized that we working on very similar projects — figuring out what to do about integer overflow bugs in C and C++ programs. Additionally, Vikram’s student Will and my student Peng had independently created [...]
Update from Friday 9/23: The SafeInt developers have already uploaded a new version that fixes the problems described in this post. Nice! I have a minor obsession with undefined behaviors in C and C++. Lately I was tracking down some integer overflows in Firefox — of which there are quite a few — and some [...]
A few weeks ago a reader left this comment: Just out of curiosity John, have you approached any of the big commercial compiler companies about getting free licenses for their products? I don’t work in the compiler business but if a university research time offered to rigorously test my software, for free, I’d say yes. [...]
[Yesterday I submitted a proposal to Google for a modest amount of money to work on turning large random programs that expose compiler flaws into concise bug reports. Below is a transcription that is mostly faithful (citations are omitted and I changed the example bug report from a floating figure into inline text). Feedback is [...]