Use the most recent taggedrelease. The include and src directories report 100% line and branch coverage, with a few exemptions made.

Overview

People say that you should not micro-optimize. But if what you love is micro-optimization... that's what you should do. - Linus Torvalds

libhatchet is a fast-compiling, lightweight, bespoke C17/C++23 alternative to the C++ standard library, designed for cross-compilation to resource-constrained targets such as DSPs, FPGAs, ASICs and WebAssembly. When a modern toolchain is unavailable it falls back to a C++11 compiler and C99 libraries, and it never depends on the C++ standard library. If you have a low-level mindset, the developer experience is better than with the standard library. Template instantiation errors are easier to read, hxassertmsg formats your assert message before setting a breakpoint for you, and there is nothing unnecessary to step through in the debugger.

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Expect shockingly fast compile times with ninja, ccache, clang and a C++ module.

The implementation stays clean under every sensible warning flag and under the GCC and Clang sanitizers, and asserts are used generously. malloc is avoided except when initializing system allocators.

Key Features

Library hardening and asserts are controlled by HX_HARDENING_MODE, for example -DHX_HARDENING_MODE=HX_HARDENING_MODE_STANDARD. See <hx/libhatchet.h> for the kinds of asserts available. Null pointer checks only happen at the debug level of hardening.
- HX_HARDENING_MODE_NONE omits library hardening and disables every assert.
- HX_HARDENING_MODE_STANDARD hardens while saving space by omitting verbose output. Meets the requirements of the C++ standard.
- HX_HARDENING_MODE_VERBOSE adds verbose messages and suits internal releases. Meets the requirements of the C++ standard.
- HX_HARDENING_MODE_DEBUG provides comprehensive asserts and verbose output.
Performance Focus: This is systems code. Everything should be optimized and cache-coherent without causing code bloat. Exceptions and RTTI are avoided for efficiency. If exceptions are enabled and one gets that far, the test driver and the console will catch it. __restrict is used extensively, and inlining attributes flatten the inner loops, as is standard practice for standard libraries.
Portability: libhatchet runs on top of any old embedded C99 library. musl libc is recommended for embedded Linux and is widely packaged: https://musl.libc.org/. No other C++ runtime or C++ code is required. Threading uses pthreads or C11's <threads.h>, both widely implemented standards. See .clang-tidy for a discussion of linting rules and portability concerns. Every public symbol other than methods and fields starts with HX or hx, and every non-public symbol in the headers ends with an underscore. A subset of the Google Test macros is also optionally provided.
Containers: A set of containers designed for environments where reallocation is not allowed. Reach for them in low-level work where the standard container libraries cause code bloat, memory fragmentation and poor cache coherence. If those are not your concerns, consider using additional libraries. No tree data structures will be provided. Exceptions are not supported for efficiency reasons, so noexcept is applied widely to defend against data loss from the unexpected use of exceptions.

There are two array classes, and both support two allocation modes:

	compile time capacity > 0	hxallocator_dynamic_capacity
hxarray	Compile-time fixed size, inline storage	Variable initial size, non-resizable, non-reallocating heap storage [1]
hxvector	Resizable, fixed capacity, inline storage	Resizable, variable initial capacity, non-reallocating heap storage

[1] Not provided by the standard.

See the headers at include/hx/ for the remaining containers. They generally use the same names as the standard.

Algorithms: The implementation uses the __restrict keyword wherever appropriate. See <hx/hxalgorithm.hpp> for the standard algorithms and <hx/hxsort.hpp> for comparison based sorting and lookup. Prefer radix sorting with <hx/hxradix_sort.hpp> when you want Θ(n) sorting. Less common functions have been omitted to reduce compile time. Random access iterators are required for a lot of things, but the only relational operator used is <. This codebase tries not to give an AI rope to hang itself with. Showing inner-loop assembly to an AI is also advised.
Memory Management: Fast and deterministic. Several allocation semantics are supported, which matters most when crashing from memory fragmentation is unacceptable. If you make a lot of temporary allocations, expect roughly 30% memory and 30% performance improvements overall from adding just a few RAII scopes. Complex applications can use an array of variable sized stacks. To use tools like heaptrack, disable the memory manager with -DHX_USE_MEMORY_MANAGER=0. Leak tracking is provided.
Testing Framework: A safer, lighter, debuggable reimplementation of the core Google Test functionality.
Fast builds: Lightweight headers result in very fast builds when used with ninja and ccache. The module loads quickly with Clang.
Pretty Printers: GDB-compatible pretty printers let debuggers and most code editors display container contents in a human-readable format.
C99 Compatibility: Logging, asserts and memory management are available in plain C99 through <hx/libhatchet.h>.
AI Friendly: Anything with the same name as the standard generally works the same way as the standard, so an AI can apply its existing knowledge of standard C++ directly. It also already knows how to use the test macros when writing tests. Using tabs instead of spaces reduces token use.
Console: An embedded command processor that binds C++ functions automatically using templates. Use it for interactive target debugging without recompilation, for config files, or for configuration from the command line. The syntax is just verb [arg ...].
Profiling System: Samples processor cycles to build a hierarchical timeline capture compatible with Chrome's chrome://tracing viewer. Navigate the capture with the W, A, S and D keys. Uncommon hardware may need one line of assembly.
Task Queue: An unopinionated task queue with priorities and a worker pool. An execution graph is also available as a layer on top.
Smart Pointers: Because the focus is non-dynamic allocation, shared and weak pointers are not provided. Use hxhandle_table for weak references instead. hxptr implements std::unique_ptr. hxoptional implements std::optional, giving the semantics of an optional temporary allocation with safe access and without the allocation itself. hxref is a non-owning pointer wrapper with the same safe access semantics.
64-bit Ready: Designed for both 32-bit and 64-bit targets. hxsize_t is signed because that enables important optimizations. It is equivalent to ptrdiff_t, but could be made 32-bit on a 64-bit platform if desired.
constexpr Ready: C++11 constexpr is used where possible. Asserts, the algorithms, hxconstexpr_list, hxbitset and hxrandom support consteval in C++23.

Documentation

The documentation is at https://whatchamacallem.github.io/libhatchet.

Run doxygen with no arguments to generate docs/index.html. The markdown source for the documentation is in the header files at include/hx/ and reads well as-is. The stylesheet was tested with Doxygen 1.15.0.

Read <hx/hxsettings.h>. A number of important things can be configured on the compiler command line, such as whether the library is wrapped in a namespace.

Not Provided

This project was started for the author's own personal use, and it tries to be complete enough for ordinary C++ programmers. It predates a lot of similar functionality in the standard. If you find something missing, odds are your favorite AI already knows how to add it, or it was omitted because the C library was deemed sufficient.

That said, some functionality of the C++ standard library is not worth reimplementing here. If you need these things, use the standard library shipped with your compiler.

Atomics. The C version of <stdatomic.h> is incompatible with g++.
The iterators library. This codebase intentionally deemphasizes iterators.
The ranges library. This would be a large and pointless rewrite.
The strings library. Strings are allocation intensive. See the {fmt} project.

Other Projects

musl libc - The recommended C library for using libhatchet in a freestanding environment.
{fmt} - A micro-optimized version of std::format, with nice extras like console colors and a fast printf.

Tested Environments

Almost every reasonable GCC and Clang warning flag should be safe to enable, and Clang-Tidy is in use. Every release is tested against glibc and musl on Ubuntu 26.04 LTS using g++-16 and clang-22. g++-10 and clang-11 are tested periodically with C++11. The latest MSVC 2022 should work with most warnings enabled, although the MSVC static analyzer is not being tested. Run debian_packages.sh to install the packages the test scripts need on a Debian based distribution such as Ubuntu.

The pico directory contains a port to the Raspberry Pi Pico 2. There is almost nothing to do when porting because libc provides almost all of the device abstraction required. Some devices require you to call the C++ global constructors yourself before calling main(). Check the sample code that came with your board.

The scripted builds exercise the following toolchains, language modes and HX_HARDENING_MODE combinations:

Script	Toolchain	Language Modes	HX_HARDENING_MODE	Notes
debugbuild.sh	clang/clang++	C17, C++23	3	32-bit debug build with ccache and no exceptions/RTTI.
testcmake.sh	cmake + default compiler	C17, C++23	3	Uses the real Google Test and runs hxtest and Clang-Tidy.
testcoverage.sh	gcc, g++ + --coverage	C99, C++23	3	Enables HX_TEST_ERROR_HANDLING=1 and emits coverage_details.html.
testmatrix.sh	gcc, clang (ASan/UBSan/TSan/MSan)	C99, C17, C++11, C++23	0-3	Sweeps optimization levels and sets HX_USE_THREADS=1/11.
teststrip.sh	musl-gcc (static)	C17, C++11/14/17/20/23	0	Size-focused static build with allocator/library stripping.
testwasm.sh	emcc	Emscripten defaults (Clang-based C/C++)	3 (default)	WebAssembly build with the memory manager disabled and pthreads enabled.

testall.sh runs all of the above and also enforces certain naming conventions.

testmsvc.bat tests 32 and 64-bit debug and release configurations on Windows and automatically discovers the installed version of MSVC.

debugbuild.sh and teststrip.sh detect when C++23 is missing and fall back to C++20 to test g++-10 and clang-11.

Project Structure

Top Level

The test scripts are at the top level for easy access. Meson and CMake scripts are also available.

📁 .vscode - The vscode configuration files.
📁 example - Simple program showing usage.
📁 gdb - GDB pretty printers, one per container, loaded by .gdbinit.
📁 include - Add this directory to your include path.
- 📁 hx - The public <hx/hx*> headers, one class per header.
  - 📁 detail - Internal implementation headers.
📁 src - The runtime implementation. Add these files to your build.
📁 test - Optional GoogleTest-style test suites.

Core layer

libhatchet.h is the entry point. It is also the header to use from C code. It provides the core macros, the assert family, memory management and feature detection, and it pulls in hxsettings.h and hxmemory_manager.h, which cannot be included directly.
Choose an HX_HARDENING_MODE on the compile line. hxassert and hxassertmsg are active only at DEBUG, hxassert_hard at STANDARD and above, and hxassert_always in every mode. Null pointer checks only happen in DEBUG.
Log through hxlog, hxlog_warning, hxlog_release and hxlog_console. They all route through hxlog_handler, which can be replaced.
hxsettings.h handles compiler detection and polyfills and documents the default for every compile-line option. Set HX_USE_NAMESPACE=<identifier> to wrap the whole library in a namespace of your choosing.
hxmemory_manager.h allocates by allocator ID. hxsystem_allocator_heap is the normal heap, hxsystem_allocator_permanent is never freed, and hxsystem_allocator_stack_0 + n selects a temporary stack that resets when the enclosing RAII hxsystem_allocator_scope closes. hxmalloc_ext takes an explicit ID, while plain hxmalloc uses the current scope.
hxutility.h provides the metaprogramming basics: hxmove, hxforward and the type traits.
hxinitializer_list.hpp either provides std::initializer_list or wraps the system version, depending on HX_USE_LIBCXX.

Containers

Differences from the standard versions are listed.

hxallocator is the static-or-dynamic capacity backing used by the containers. Prefer static capacities where allocation is a concern.
hxarray is the fixed-size std::array analog. hxvector covers both std::vector and std::inplace_vector. Both have the algorithms as methods: find, find_if, all_of, any_of, for_each, binary_search, sort and insertion_sort. Both provide get(index) returning hxnull when out of range, size_bytes, memcpy/memset fills and construction and assignment from C-style arrays. hxvector adds full, Python-style operator+= append and concatenate, generate_n, Θ(1) erase_unordered and erase_if_unordered, and make_heap/push_heap/pop_heap/ erase_if_heap, which replace std::priority_queue. An hxvector also works directly as an output iterator, replacing std::back_insert_iterator.
hxdeque is a fixed-capacity ring buffer with a power-of-two capacity. Every operation, including operator[], is Θ(1), and full is provided.
hxbitset is a fixed-size bit set stored in size_t words with no heap use. Unlike std::bitset it exposes the underlying words via data and bytes and loads raw bytes with load. Shifts and bitwise operators are provided.
hxlist is an intrusive doubly linked XOR list at half the size of a conventional one. hxconstexpr_list has the same interface but uses normal pointers so it works in constexpr code. Nodes are owned through a configurable deleter, and subclasses of the node type may be stored heterogeneously. extract, pop_front and pop_back return an owning hxptr, release_all abandons ownership, and remove_if, splice and reverse are provided.
hxflat_map and hxflat_set are sorted parallel-array replacements for map/multimap and set/multiset. Expect O(log2(n)) lookups and O(n) insertions and removals. find returns a pointer to the mapped value or hxnull instead of an iterator, and elements are addressable by position with operator[] and get.
hxhash_table is a fixed-size hash table with singly linked buckets embedded in the nodes. Additional node types are in hxhash_table_nodes.hpp. find(key, previous) walks duplicate keys without equal_range, replace swaps a node in with a single lookup, extract returns an owning hxptr, and release_all and release_key unlink nodes without deleting them. load_factor and load_max report bucket usage.
hxhandle_table maps handles to pointers and hxhandle_map maps handles to values. Both use 64-bit generational handles, so use them when stale references need to be detected. Both provide erase_if and extract. hxhandle_map is a slot map keeping its values contiguous for iteration.
hxfree_list is a fixed-capacity free-list allocator built on hxallocator. allocate and try_allocate construct a T and return an hxptr whose deleter returns the slot to the pool. is_allocator tests whether a pointer came from the pool.
hxoptional implements std::optional<T>, hxref implements std::optional<T&>, which the standard does not provide before C++26, and hxptr is a unique owning pointer with a monadic and_then and a deleter that may decline deletion, e.g. hxdo_not_delete.
Every keyed container and sort compares keys through the free functions hxkey_equal, hxkey_less and hxkey_hash in hxkey.hpp. Overload them for custom key types. The defaults require only == and <.
Containers with dynamic capacity move and hxswap in Θ(1) without touching elements.

Algorithms

Differences from the standard versions are listed.

hxalgorithm.hpp provides searching and set utilities taking callables: hxall_of, hxany_of, hxcount_if, hxexchange, hxfind_if, hxfor_each, hxmerge, hxminmax, hxset_difference, hxset_intersection, hxset_union and hxunique. hxmerge and the set operations move-assign out of their inputs and accept an hxvector reference directly as the output iterator, appending to it without std::back_inserter, e.g. hxmerge<const int*, hxvector<int>&>(...). hxminmax returns a result with min and max iterator fields in a single pass.
hxsort.hpp provides the comparison sorts and lookup. hxsort is an introsort, and hxinsertion_sort and hxheapsort are also available. hxbinary_search, hxlower_bound and hxupper_bound are provided, and unlike std::binary_search, hxbinary_search returns an iterator to the first match instead of bool.
Every comparison routes through the hxkey_less and hxkey_equal free functions or an explicit callable, so custom key types overload two free functions once instead of passing comparators everywhere.
For scalar keys up to 32 bits, hxradix_sort sorts in Θ(n) time. Its implementation is in src/hxradix_sort.cpp. It sorts hxradix_sort_key<key_t, value_t> pairs and handles signed and float keys with bit manipulation. hxradix_sort11 uses 11-bit digits for large workloads, and the temporary buffers come from a caller-selected memory manager allocator ID.
hxrandom is a 64-bit LCG intended for generating test data. Beyond operator() it provides u8/u16/u32/u64, f01/d01 in [0..1), range(base, size) overloads that use a floating point multiply instead of integer modulo, read to fill a buffer with random bytes, and independently seeded streams. It works in constexpr code, so random test data can be built at compile time.

Runtime Facilities

hxfile is RAII file I/O. HX_USE_FILE_IO selects the backend: 1 is the libc backend in src/hxfile_c.cpp and 2 is the POSIX backend in src/hxfile_posix.cpp.
hxconsole is a debug and remote command console that also parses config files such as example.cfg. Register bindings at file scope with hxconsole_command() and hxconsole_variable(), or use the _named variants to choose the name yourself.
hxprofiler is a cycle-sampling scope profiler that emits chrome://tracing captures. Mark a scope with hxprofile_scope("label") and control capture with hxprofiler_start(), hxprofiler_stop() and hxprofiler_log(). It compiles away entirely unless HX_USE_PROFILER=1.
hxtask and hxtask_queue form a worker-pool priority queue. hxtask_dag_node layers DAG dependencies on top.
hxthread wraps pthreads or C11 <threads.h> with hxmutex, hxcondition_variable, hxunique_lock, hxthread and hxthread_local.
hxtest is the GoogleTest-compatible subset that the test suite itself runs on. Set HX_USE_GOOGLE_TEST=1 to run the same tests against the real Google Test.

License

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