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Fun with -fsanitize=undefined and Picolibc Both GCC and Clang support the -fsanitize=undefined flag which instruments the generated code to detect places where the program wanders into parts of the C language specification which are either undefined or implementation defined. Many of these are also common programming errors. It would be great if there were sanitizers for other easily detected…
Internationalization support in Picolibc There are two major internationalization APIs in the C library: locales and iconv. Iconv is an isolated component which only performs charset conversion in ways that don't interact with anything else in the library. Locales affect pretty much every API that deals with strings and covers charset conversion along with a huge range of localized information…
Testing Picolibc with the glibc tests Picolibc has a bunch of built-in tests, but more testing is always better, right? I decided to see how hard it would be to run some of the tests provided in the GNU C Library (glibc). Parallel meson build files Similar to how Picolibc uses meson build files to avoid modifying the newlib autotools infrastructure, I decided to take the glibc code and write meson…
Reviving Very Old X Code I've taken the week between Christmas and New Year's off this year. I didn't really have anything serious planned, just taking a break from the usual routine. As often happens, I got sucked into doing a project when I received this simple bug report Debian Bug #974011 I have been researching old terminal and X games recently, and realized that much of the code from…
Picolibc Updates I thought work on picolibc would slow down at some point, but I keep finding more things that need work. I spent a few weeks working in libm and then discovered some important memory allocation bugs in the last week that needed attention too. Cleaning up the Picolibc Math Library Picolibc uses the same math library sources as newlib, which includes code from a range of sources:…
Float/String Conversion in Picolibc: Enter “Ryū” I recently wrote about this topic having concluded that the best route for now was to use the malloc-free, but imprecise, conversion routines in the tinystdio alternative. A few days later, Sreepathi Pai pointed me at some very recent work in this area: Ryū: Fast Float-to-String Conversion (PLDI 2019) Ryū revisited: printf floating point conversion…
Float/String Conversion in Picolibc Exact conversion between strings and floats seems like a fairly straightforward problem. There are two related problems: String to Float conversion. In this case, the goal is to construct the floating point number which most closely approximates the number represented by the string. Float to String conversion. Here, the goal is to generate the shortest string…
Slightly Better Iterative Spline Decomposition My colleague Bart Massey (who is a CS professor at Portland State University ) reviewed my iterative spline algorithm article and had an insightful comment — we don't just want any spline decomposition which is flat enough, what we really want is a decomposition for which every line segment is barely within the specified flatness value. My initial…
Decomposing Splines Without Recursion To make graphics usable in Snek, I need to avoid using a lot of memory, especially on the stack as there's no stack overflow checking on most embedded systems. Today, I worked on how to draw splines with a reasonable number of line segments without requiring any intermediate storage. Here's the results from this work: The Usual Method The usual method I've…
Prototyping a Vulkan Extension — VK_MESA_present_period I've been messing with application presentation through the Vulkan API for quite a while now, first starting by exploring how to make head-mounted displays work by creating DRM leases as described in a few blog posts: 1 , 2 , 3 , 4 . Last year, I presented some work towards improving frame timing accuracy at the X developers conference . Part…