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add xsimd (#549)
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‎.agents/docs/2026-10-20-add-xsimd-plan.md‎

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# Add xsimd 14.3.0 as compat.xsimd
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## Source and shape
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- Upstream: <https://github.com/xtensor-stack/xsimd>.
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- Version: `14.3.0`, the newest stable tag observed with
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`git ls-remote --tags --refs`.
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- License: BSD-3-Clause.
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- Shape: Form B, header-only. Upstream's CMake INTERFACE target exposes
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`include/`, where consumers find `<xsimd/xsimd.hpp>`. The package therefore
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uses `include_dirs = { "*/include" }` and a trivial anchor C TU to provide a
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buildable `xsimd` lib target.
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- No features: xsimd has no optional compilable library component. The
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optional `xtl::xcomplex` integration is an external dependency plus the
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consumer's `XSIMD_ENABLE_XTL_COMPLEX` define, which a sources-only feature
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cannot express.
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Upstream requires C++14. The descriptor compiles its own anchor as C++; the
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consumer test uses the workspace default C++23 mode and a direct smoke test
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also verifies that the public header compiles in C++14 mode.
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## Download and mirror
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- GLOBAL:
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`https://github.com/xtensor-stack/xsimd/archive/refs/tags/14.3.0.tar.gz`
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- SHA-256:
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`b3d50e7a73fbf4642ceef30131c93414901d69eee41c2a5302db650b03e2c792`
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- The archive was downloaded twice and compared byte-for-byte; both copies had
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the same digest.
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- No verified `mcpp-res/xsimd` release is available, so the descriptor uses the
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upstream plain-string URL fallback rather than inventing a CN resource.
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## Automatic updates
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The package meets the automatic-update criteria: it has GitHub numeric tags,
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stable archive URLs, identical resources on all declared platforms, and future
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versions do not require a build-recipe change. `extensions.autoupdate` uses the
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unprefixed `${version}` tag spelling and the GitHub tag-archive URL template.
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The initial URL and SHA-256 live once in the `versions` table and all three
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platforms reference that entry.
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## Test member
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`tests/examples/xsimd/` is registered in the root workspace. It asserts:
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- the selected default architecture is supported and available;
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- runtime architecture discovery contains the default architecture;
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- unaligned load, batch addition and unaligned store preserve every lane;
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- batch square root and horizontal reduction return the expected scalar.
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Every assertion affects the process exit status (`return ok ? 0 : 1`).
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## Verification
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- Pinned mcpp `2026.10.1.2`:
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`mcpp xpkg parse --all-os pkgs/c/compat.xsimd.lua` reports `parse OK` for
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linux, macosx, and windows.
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- Pinned cold GCC run:
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`mcpp test -p xsimd --cache off` reports
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`test result ok. 1 passed; 0 failed`, running
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`xsimd OK width=4 arch=sse2`.
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- Pinned cold LLVM run:
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`mcpp test -p xsimd --toolchain llvm@22.1.8 --cache off` reports the same
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successful test with Clang.
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- The public header and test compile and run directly under both C++14 and
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C++23 (GCC 16.2.1), covering xsimd's documented language floor.
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- Full relevant lint passed: Lua syntax, mirror URL policy, package identity,
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reserved namespaces, cross-package references, platform parity, and
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duplicate versions. All 255 descriptors parse with the pinned mcpp.
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- The pinned updater's 11 repository tests pass. Its declaration coverage audit
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reports `All 83 GitHub-direct descriptors declared; all existing versions
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unchanged`, including `compat:xsimd`.
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- `xpkgindex_update inspect --package compat:xsimd` accepts the declaration and
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reports the three platform URLs plus the automatic-update template.
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- `xpkgindex_update check --package compat:xsimd` reports
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`status = "up-to-date"`, current version `14.3.0`, discovery by upstream
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tags. An earlier attempt hit the unauthenticated GitHub API rate limit; the
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check passed after the documented reset window.

‎mcpp.toml‎

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"tests/examples/websocket-features",
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"tests/examples/websocket-tls",
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"tests/examples/tray",
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"tests/examples/xsimd",
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"tests/examples/xxhash",
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"tests/examples/yaml-cpp",
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"tests/examples/yaml-cpp-v080",

‎pkgs/c/compat.xsimd.lua‎

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local versions = {
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["14.3.0"] = {
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url = "https://github.com/xtensor-stack/xsimd/archive/refs/tags/14.3.0.tar.gz",
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sha256 = "b3d50e7a73fbf4642ceef30131c93414901d69eee41c2a5302db650b03e2c792",
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},
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}
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-- Form B inline descriptor for xsimd — C++ wrappers over SIMD intrinsics.
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--
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-- HEADER-ONLY: upstream's CMake target exposes exactly `include/`, where
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-- consumers find `<xsimd/xsimd.hpp>`. Tests, examples, benchmarks and docs
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-- stay outside the include path. A trivial anchor TU gives mcpp a buildable
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-- `xsimd` lib target, following compat.gtl / compat.safeint.
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--
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-- LANGUAGE FLOOR: xsimd requires C++14 (`target_compile_features` says
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-- `cxx_std_14`). The package's own anchor is compiled as C++; consumers may
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-- use any C++14-or-newer language mode supported by their toolchain.
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--
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-- No features: xsimd is header-only and has no optional compilable library
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-- component. Its optional `xtl::xcomplex` integration is controlled by the
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-- consumer's XSIMD_ENABLE_XTL_COMPLEX define and an external xtl dependency,
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-- so a sources-only feature cannot represent it and is deliberately omitted.
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--
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-- No verified mcpp-res mirror is available, so the upstream URL is a plain
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-- string rather than a fabricated GLOBAL/CN resource table.
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package = {
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spec = "1",
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namespace = "compat",
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name = "xsimd",
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description = "C++ wrappers for SIMD intrinsics with runtime architecture selection (header-only)",
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licenses = {"BSD-3-Clause"},
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repo = "https://github.com/xtensor-stack/xsimd",
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type = "package",
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extensions = {
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autoupdate = {
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tag = "${version}",
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url = "https://github.com/xtensor-stack/xsimd/archive/refs/tags/${tag}.tar.gz",
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},
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},
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xpm = {
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linux = {
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["14.3.0"] = versions["14.3.0"],
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},
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macosx = {
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["14.3.0"] = versions["14.3.0"],
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},
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windows = {
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["14.3.0"] = versions["14.3.0"],
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},
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},
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mcpp = {
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language = "c++23",
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import_std = false,
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c_standard = "c11",
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include_dirs = { "*/include" },
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generated_files = {
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["mcpp_generated/xsimd_anchor.c"] = [==[
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int mcpp_compat_xsimd_headers_anchor(void) { return 0; }
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]==],
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},
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sources = { "mcpp_generated/xsimd_anchor.c" },
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targets = { ["xsimd"] = { kind = "lib" } },
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deps = { },
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},
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}

‎tests/examples/xsimd/mcpp.toml‎

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# xsimd test project: exercise the default architecture selected from the
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# consumer's compiler flags, plus load/store and useful batch operations.
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[package]
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name = "xsimd-tests"
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version = "0.1.0"
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[dependencies.compat]
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xsimd = "14.3.0"

‎tests/examples/xsimd/tests/xsimd.cpp‎

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// compat.xsimd — assert architecture discovery, unaligned load/store, batch
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// arithmetic, math functions and horizontal reduction through the public API.
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#include <xsimd/xsimd.hpp>
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#include <array>
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#include <cmath>
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#include <cstddef>
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#include <cstdio>
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int main() {
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using batch_type = xsimd::batch<float>;
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constexpr std::size_t width = batch_type::size;
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std::array<float, width> left{};
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std::array<float, width> right{};
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std::array<float, width> sum{};
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for (std::size_t i = 0; i < width; ++i) {
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left[i] = static_cast<float>(i + 1);
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right[i] = static_cast<float>(2 * i + 2);
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}
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bool ok = true;
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auto check = [&](bool condition, const char* what) {
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if (!condition) {
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std::printf("FAIL: %s\n", what);
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ok = false;
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}
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};
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check(xsimd::default_arch::supported(),
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"default architecture is supported by the compiler");
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check(xsimd::default_arch::available(),
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"default architecture is available on this CPU");
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check(xsimd::available_architectures().has(xsimd::default_arch{}),
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"runtime discovery includes the default architecture");
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auto lhs = xsimd::load_unaligned(left.data());
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auto rhs = xsimd::load_unaligned(right.data());
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xsimd::store_unaligned(sum.data(), lhs + rhs);
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for (std::size_t i = 0; i < width; ++i) {
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check(sum[i] == left[i] + right[i],
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"unaligned load, batch addition and store");
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}
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auto square_roots = xsimd::sqrt(lhs * lhs);
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const float expected = static_cast<float>(width * (width + 1) / 2);
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check(std::fabs(xsimd::reduce_add(square_roots) - expected) < 0.001f,
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"batch math and horizontal reduction");
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if (ok) {
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std::printf("xsimd OK width=%zu arch=%s\n",
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width, xsimd::default_arch::name());
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}
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return ok ? 0 : 1;
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}

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