A from-scratch C library for WebAssembly. The name comes from Gary Bernhardt's The Birth & Death of JavaScript — a vision of "metal" web applications running at near-native speed. Metallic aims to be the runtime for that world.

# Build the libraries (requires clang with the wasm32 target and llvm-link).
make

# Run the included hello-world example under wasmtime.
cd examples/hello && make run

Metallic builds to a single static archive, metallic.a, that calls WASI snapshot_preview1 directly. Programs link it like any other library:

clang --target=wasm32-unknown-unknown-wasm -nostdlib \
    -I include main.c metallic.a -o app.out

Host I/O lives in src/wasi/wasi.h, where each binding carries the import_module("wasi_snapshot_preview1") attribute so the linker emits them as wasm imports without needing --allow-undefined.

Implemented C11 hosted-environment headers:

• <assert.h> <complex.h> <ctype.h> <errno.h> <fenv.h> <float.h> <inttypes.h> <iso646.h> <limits.h> <locale.h> <math.h> <setjmp.h> <signal.h> <stdalign.h> <stdarg.h> <stdbool.h> <stddef.h> <stdint.h> <stdio.h> <stdlib.h> <stdnoreturn.h> <string.h> <tgmath.h> <time.h> <uchar.h> <wchar.h> <wctype.h>

Opted out via __STDC_NO_THREADS__: <threads.h> is intentionally not shipped. <stdatomic.h> comes from clang's freestanding headers and lowers to plain operations on single-threaded WASI.

Correct rounding is the math library's goal, and every real float and double transcendental now reaches it (the complex functions are composed from those kernels and inherit their accuracy). A function is correctly rounded when its result is the true value rounded to the nearest representable number (error ≤ 0.5 ulp); faithfully rounded is the weaker guarantee of one of the two nearest (error < 1 ulp). For float, correct rounding is proven by an exhaustive sweep of all 2³² bit patterns against an MPFR or CORE-MATH oracle; for double it is strong evidence from a sampler that hammers the published hard-to-round cases plus a broad random sample. See test/oracle/ and make check.oracle (native; not part of the wasm CI gate).

• float, correctly rounded (≤ 0.5 ulp). Unary, proven by exhaustive sweep: expf exp2f expm1f logf log2f log10f log1pf sinf cosf tanf asinf acosf atanf asinhf acoshf atanhf sinhf coshf tanhf cbrtf erff erfcf lgammaf tgammaf. Bivariate (sampler evidence, since the 2⁶⁴ domain cannot be swept): atan2f hypotf powf.
• double, correctly rounded (≤ 0.5 ulp), sampler evidence. Unary: exp exp2 expm1 log log2 log10 log1p sin cos tan asin acos atan asinh acosh atanh sinh cosh tanh cbrt erf erfc lgamma tgamma. Bivariate (sampler evidence, since the 2⁶⁴ domain cannot be swept): atan2 hypot pow.
• Complex float, correctly rounded (≤ 0.5 ulp per part), sampler evidence. Each of the real and imaginary parts is the correctly-rounded float of the exact value (the 2⁶⁴ domain cannot be swept, so this is a random + near-axis MPFR sampler, as for the bivariate floats): cabsf cargf csqrtf cexpf clogf. See test/oracle/math/float/complex/ and make check.oracle.complex. The remaining complex float functions (the trig/hyperbolic and inverse families, cpowf) are still composed from the real kernels and faithful.
• Complex double (cabs, cexp, clog, csqrt, the trig/hyperbolic families, …) is composed from the real kernels and inherits their accuracy.

• longjmp aborts the process. WebAssembly has no native stack unwinding; programs that need real setjmp/longjmp should compile with clang's -mllvm -wasm-enable-sjlj, which lowers setjmp/longjmp to clang intrinsics and bypasses libc.
• signal/raise track handlers but do not asynchronously dispatch — WASI preview1 delivers no signals. raise(SIGABRT) is correctly routed.
• localtime aliases gmtime — WASI preview1 has no timezone info.
• Only the C locale is supported.
• No threads. __STDC_NO_THREADS__ is predefined, so <threads.h> is absent and feature-test code routes around the C11 thread API. Atomics use clang's freestanding <stdatomic.h>; on single-threaded WASI they lower to plain loads and stores.

• make check.native — native tests (some pre-existing math accuracy failures against the host libm).
• make check.wasm.fast — wasm tests under wasmtime, excluding the 11 pre-existing soft-float/integer/long-double failures. CI runs this.
• make check.wasm — full wasm suite including the known-broken tests.

If wasmtime is installed but not on PATH (for example via $HOME/.wasmtime/bin/wasmtime), the Makefile will use that location automatically. You can also select another runner explicitly:

make WASMRUN=/path/to/wasmtime check.wasm.fast

11 pre-existing test failures in the soft-float / 128-bit integer / long-double sqrt code paths. These are not regressions and are excluded from check.wasm.fast. See Makefile KNOWN_BROKEN_WASM.

This was originally Chen-Pang He's libc-for-WebAssembly experiment. Revival work brought it up to a hosted C11 + WASI snapshot_preview1 runtime; the math kernels predate the revival.

See LICENSE.