snippets

Container repo with very simple code snippets. All code should compile cleanly with either clang or gcc. Dependencies have been kept to a minimum; only standard C library functions are required (except for the gnu modular make snippet which is kind of obvious).

• circbuffer: circular buffer that allows 1 reader and 1 writer to operate on it, lock free.

• uintxx: customizable width unsigned integer operations, multiply, divide, shift left and shift right.

• ecvt-strtod: currently only ecvt implementation. Convert a 64 or 32 bit IEEE754 double into character digits; rounding to nearest even or not, can be selected. For scaling up and down, it makes use of the uintxx code mentioned above. There's some sample code that can be build as follows, from within the ecvt-strtod folder:

  gcc -m32 -Wall -Wsign-conversion -Wextra -Wno-unused-parameter -I . -I ../uintxx *.c ../uintxx/uintxx.c -o sample
  ./sample
  1.3806515690000000e-23 printf
  1.3806515690000000e-23 sbtecvt
  3.14159274 sbtecvt

  The code works for both 32 bit and 64 bit CPUs, so therefore the -m32. Leave this command line option out for the 64 bit version. Also big or little endianess shouldn't matter.

  This blog entry of Victor Zverovich was an inspiration for the code to convert the IEEE754 format.

• customizable-printf: printf where one can add new format characters and the code how they should be rendered. Has implementations for most format characters of printf. There's a bit of sample code to show its usage. For the double formatting (e, g, f) it makes use of the ecvt implementation described earlier. There's a super simple Makefile to build the sample.

• gnu-4.x-modular-make: implementation of a sample loadable module for GNU Make 4.x. It allows subfolders with implementation code for libraries. Applications and libraries can express imports they need and they will be properly handled by the code. There's not more documentation for the moment. Contact me if you are interested.

• snset: a simple implementation of an object allocator; if you need to create a set of objects that may have a dynamic tail end (variable sized) and you want the result to be a single block of memory (e.g. for memory efficiency reasons), this will help in creating that block of objects. There is sample code showing how to use the set. To build from the snset folder:

  clang -I . snset.c sample.c -o sample
  ./sample

• hexdump: create a canonical hexdump in a given character buffer. Always terminate the dump, even if the buffer is too small.

• delta-timers: implement a multitude of timers by means of a linked list with each timer/element having a delta relative timeout wrt the previous timer in the list, so when evaluating the timeout, only the first element/timer needs to be checked. There is a small snippet of sample code, using a pthread as a timer ticker thread.

  clang -Os -Wall -I . *.c -o sample -lpthread
  ./sample # run until ctrl-c

• txt-tr-utils: a small set of in place text transformation functions. They are all very simple. None of them implement any checking for the buffer size being large enough. Simple, yet I was getting annoyed by the number of times I re-implemented -and debugged- them from scratch each time.

• t2c-types: a set of utilities to create, manipulate and analyze structure types, union types, enums and bitsets. Could prove useful in code generation tools. Can cluster fields that are governed by the same member for size, together. Can optimize a type to avoid padding as much as possible, by reordering members. No sample code.

• fb2: the very early start of a flatbuffer schema parser. It parses a flatbuffer schema into an internal format that can be used for further processing (tool creation, code generation, ...). Uses the above mentioned snset for processing and generating the internal schema. Requires flex (>= 2.6.4) and bison (>= 3.6.0) for scanner and parser generation. The code generation part will create the control structures necessary for walking over and creating a flatbuffer from a graph. No sample code or documentation (yet).

• avalanche: a hash avalanche test. The sample code uses the avalanche test to compare 3 different hashes; murmur3, lookup3 and a buzhash added for comparison. The murmur3 and lookup3 source code files contain the original copyrights. Only the lookup3 source code file was slightly modified so it could be compiled and linked into the sample. The test can use a deterministic mean of flipping the bits or a random mode; ensure the test count is high enough for statistical relevance, in the random mode. RNG seeding is not done by the test and needs to be added manually, if needed. Compile sample with

  clang -I . -Wall -Os -o sample sample.c lookup3.c sbtbuz2.c murmurhash.c avalanche.c

  and run ./sample.

• sbt-utils: implementations for strlcat and strlcpy based upon the canonical paper found here. The other function included is resolvepath which is essentially an implementation of the Posix realpath function but not relying on the PATH_MAX system limit but where the buffersize is passed as an argument. This paper arguments why using PATH_MAX is a wrong approach anyway. Compile sample with

  clang -Wall -Werror -Os -I ./ -o sample sample.c resolvepath.c strlcpy-cat.c

• bluetooth: header files that embodiess the Bluetooth 5.3 and 5.4 Host Controller Interface specification commands and events that can be exchanged. The result of some experimenting with regular expressions on the specification text. The parser itself is too kludgy to release but the result could be useful for people that want to create a code generator for encoding/decoding HCI messages or test pattern generation, debugging, etc. There is a README in the folder itself and an embryonic encoder decoder has been added in the codec folder, together with some sample code on how to use it.

• u-locks: some proof of concept code of micro locking a linked list and manipulating it with several mutator threads. Uses optimistic synchronization and gcc/clang builtin atomic operations to achieve multi-threaded correctness. Single Makefile and single source file; just a proof of concept. There's more documentation in the u-locks.md file.

• umem: a micro memory manager for allocating and releasing blocks of memory, much like standard malloc and free. It uses microlocks on each chunk of memory, in stead of a global mutex for which OS support is required. Main use is in embedded systems.

• aes-ecb-cmac: yet another AES ECB and CMAC implementation. Does not claim to be safe. The provided sample runs some AES known answer test vectors and some CMAC test cases. The required K1 or K2 CMAC key is only generated at the finishing step. There are no dependencies to any libc function except memcpy and memset. If the ECB state needs clearing because of side channel leakage prevention, this needs to be done by the caller. See the sample code.

  $ cd aes-ecb-cmac/
  $ gcc -Os -o sample -Wall -Werror -Wconversion -I . sample.c yaes.c
  $ ./sample
  Done 12 ECB tests.
  Done 13 AES CMAC tests.