WebAssembly

Source: examples/wasm/

Cross-compile Fortran to WebAssembly using Emscripten.

Prerequisites

Add emsdk to your MODULE.bazel:

bazel_dep(name = "emsdk", version = "4.0.17")

3.A. Hello World

wasm/
├── BUILD.bazel
└── hello.f90

program hello
    implicit none
    print *, "Hello from wasm32 with rules_fortran!"
end program hello

fortran_library(
    name = "hello",
    srcs = ["hello.f90"],
)

cc_binary(
    name = "hello_cc",
    srcs = [],
    deps = [":hello"],
)

wasm_cc_binary(
    name = "hello_wasm",
    cc_target = ":hello_cc",
    outputs = ["hello_cc.js", "hello_cc.wasm"],
)

bazel build //wasm:hello_wasm
node bazel-bin/wasm/hello_cc.js

Hello from wasm32 with rules_fortran!

The cc_binary target works as a native executable. Wrapping it with wasm_cc_binary produces WebAssembly output instead.

3.B. LAPACK

wasm/
├── BUILD.bazel
└── full.c

#include <lapacke.h>
#include <stdio.h>

int main() {
    float A[9] = {1, 2, 3, 4, 5, 6, 7, 8, 10};
    int ipiv[3];
    int info = LAPACKE_sgetrf(LAPACK_COL_MAJOR, 3, 3, A, 3, ipiv);

    printf(info ? "FAIL\n" : "OK\n");
    for (int i = 0; i < 9; i++)
        printf("%8.2f%c", A[i], (i+1)%3 ? ' ' : '\n');
    return info;
}

cc_binary(
    name = "full",
    srcs = ["full.c"],
    deps = [
        "@blas//:single",
        "@lapack//:single",
        "@lapacke//:single",
    ],
)

wasm_cc_binary(
    name = "full_wasm",
    cc_target = ":full",
    outputs = ["full.js", "full.wasm"],
)

bazel build //wasm:full_wasm
node bazel-bin/wasm/full.js

OK
    3.00     0.33     0.67
    6.00     2.00     0.50
   10.00     3.67    -0.50

3.C. OpenMP (pthreads)

OpenMP parallel region running in wasm32 with emscripten pthreads.

wasm/
├── BUILD.bazel
└── omp_hello.f90

program omp_hello
    use omp_lib
    implicit none
    integer :: tid, nthreads

    !$omp parallel private(tid)
    tid = omp_get_thread_num()
    nthreads = omp_get_num_threads()
    print *, "thread", tid, "of", nthreads
    !$omp end parallel
end program omp_hello

fortran_library(
    name = "omp_hello",
    srcs = ["omp_hello.f90"],
    copts = ["-fopenmp", "-pthread"],
    deps = ["@libomp"],
)

cc_binary(
    name = "omp_hello_cc",
    srcs = [],
    linkopts = ["-pthread"],
    deps = [":omp_hello"],
)

wasm_cc_binary(
    name = "omp_hello_wasm",
    cc_target = ":omp_hello_cc",
    outputs = ["omp_hello_cc.js", "omp_hello_cc.wasm"],
    threads = "emscripten",
)

bazel build //wasm:omp_hello_wasm
node bazel-bin/wasm/omp_hello_cc.js

 thread 0 of 16
 thread 2 of 16
 thread 1 of 16
 thread 3 of 16
 thread 8 of 16
 thread 9 of 16
 thread 11 of 16
 thread 7 of 16
 thread 4 of 16
 thread 10 of 16
 thread 5 of 16
 thread 12 of 16
 thread 13 of 16
 thread 14 of 16
 thread 6 of 16
 thread 15 of 16