Full no_std and miri support

.github/workflows/release.yaml

@@ -64,6 +64,7 @@ jobs:
           args: --release
 
   miri-test:
+    name: no_std and miri
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -101,9 +102,14 @@ jobs:
         with:
           toolchain: ${{ steps.versions.outputs.rustc }}
           profile: minimal
-          components: miri
+          components: miri, rust-src
           override: true
 
+      - name: Test `no_std` compatibility
+        shell: bash
+        working-directory: ensure_no_std
+        run: cargo +${{ steps.versions.outputs.rustc }} build
+
       - name: Run tests in miri
         env:
           RUSTFLAGS: "-Zrandomize-layout"

.github/workflows/test.yaml

@@ -82,6 +82,7 @@ jobs:
           args: --release
 
   miri-test:
+    name: no_std and miri
     runs-on: ${{ matrix.os }}
     needs: rust-test
     strategy:
@@ -131,9 +132,14 @@ jobs:
         with:
           toolchain: ${{ steps.versions.outputs.rustc }}
           profile: minimal
-          components: miri
+          components: miri, rust-src
           override: true
 
+      - name: Test `no_std` compatibility
+        shell: bash
+        working-directory: ensure_no_std
+        run: cargo +${{ steps.versions.outputs.rustc }} build
+
       - name: Run tests in miri
         env:
           RUSTFLAGS: "-Zrandomize-layout"

Cargo.toml

@@ -20,7 +20,7 @@ name = "constriction"
 
 [features]
 default = ["std"]
-std = ["probability"]
+std = []
 
 # Use feature `pybindings` to compile the python extension module that provides
 # access to this library from python. This feature is turned off by default
@@ -30,10 +30,11 @@ pybindings = ["ndarray", "numpy", "pyo3"]
 
 [dependencies]
 hashbrown = "0.12.3"
-num = "0.4"
+num-traits = {version = "0.2.15", default-features = false, features = ["libm"]}
 smallvec = "1.6.1"
 
-probability = {version = "0.18", optional = true}
+libm = "0.2.6"
+probability = {version = "0.20"}
 
 ndarray = {version = "0.15", optional = true}
 numpy = {version = "0.17.1", optional = true}

benches/lookup.rs

@@ -10,7 +10,7 @@ use constriction::{
     BitArray, Pos, Seek,
 };
 use criterion::{black_box, criterion_group, Criterion};
-use num::cast::AsPrimitive;
+use num_traits::AsPrimitive;
 use rand::{RngCore, SeedableRng};
 use rand_xoshiro::Xoshiro256StarStar;
 
@@ -26,7 +26,7 @@ criterion_group!(
 #[cfg(not(miri))]
 criterion::criterion_main!(benches);
 #[cfg(miri)]
-fn main() {} // All benchmarks currently use FFI and therefore can't be tested in miri.
+fn main() {} // miri currently doesn't seem to be able to run criterion benchmarks as tests.
 
 fn round_trip_u32_u64_u16_12(c: &mut Criterion) {
     round_trip::<u32, u64, u16, 12>(c);
@@ -87,7 +87,7 @@ where
         type_name::<Probability>(),
         PRECISION
     );
-    c.bench_function(&format!("ans_encoding_{}", label_suffix), |b| {
+    c.bench_function(&format!("ans_encoding_{label_suffix}"), |b| {
         b.iter(|| {
             encoder.clear();
             encoder
@@ -109,7 +109,7 @@ where
     let mut backward_decoder = encoder.into_seekable_decoder();
     let reset_snapshot = backward_decoder.pos();
 
-    c.bench_function(&format!("ans_backward_decoding_{}", label_suffix), |b| {
+    c.bench_function(&format!("ans_backward_decoding_{label_suffix}"), |b| {
         b.iter(|| {
             backward_decoder.seek(black_box(reset_snapshot)).unwrap();
             let mut checksum = 1234u16;
@@ -132,7 +132,7 @@ where
     let mut forward_decoder = backward_decoder.into_reversed();
     let reset_snapshot = forward_decoder.pos();
 
-    c.bench_function(&format!("ans_forward_decoding_{}", label_suffix), |b| {
+    c.bench_function(&format!("ans_forward_decoding_{label_suffix}"), |b| {
         b.iter(|| {
             forward_decoder.seek(black_box(reset_snapshot)).unwrap();
             let mut checksum = 1234u16;
@@ -179,7 +179,7 @@ where
         type_name::<Probability>(),
         PRECISION
     );
-    c.bench_function(&format!("range_encoding_{}", label_suffix), |b| {
+    c.bench_function(&format!("range_encoding_{label_suffix}"), |b| {
         b.iter(|| {
             encoder.clear();
             encoder
@@ -200,7 +200,7 @@ where
 
     let mut decoder = encoder.into_decoder().unwrap();
 
-    c.bench_function(&format!("range_decoding_{}", label_suffix), |b| {
+    c.bench_function(&format!("range_decoding_{label_suffix}"), |b| {
         b.iter(|| {
             decoder.seek(black_box(reset_snapshot)).unwrap();
             let mut checksum = 1234u16;

ensure_no_std/.cargo/config.toml

@@ -0,0 +1,21 @@
+# We need to cross-compile the core library.
+[unstable]
+build-std = [
+  "alloc",
+  "compiler_builtins",
+  "core",
+]
+build-std-features = ["compiler-builtins-mem"]
+
+[build]
+rustflags = [
+  # See https://doc.rust-lang.org/rustc/codegen-options/index.html for possible rustflags
+  # use custom linker script
+  "-C",
+  "link-args=-n -T src/link.ld", # The default of the x86_64-unknown-none built-in Rust compiler target is "pic".
+  # See: https://github.com/rust-lang/rust/blob/1.62.1/compiler/rustc_target/src/spec/x86_64_unknown_none.rs
+  # This is not supported by Hedron.
+  "-C",
+  "relocation-model=static",
+]
+target = "x86_64-unknown-none"

ensure_no_std/.gitignore

@@ -0,0 +1 @@
+/target