Fix building on 32bit platforms

Signed-off-by: Nico Burns <[email protected]>

Author: nicoburns

.github/workflows/ci.yml

@@ -98,7 +98,7 @@ jobs:
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ env.RUST_STABLE_VER }}
-          targets: x86_64-unknown-none
+          targets: x86_64-unknown-none,thumbv8m.main-none-eabihf
           components: clippy
 
       - name: install cargo-hack
@@ -114,6 +114,9 @@ jobs:
       - name: cargo clippy (no_std)
         run: cargo hack clippy --workspace --locked --optional-deps --each-feature --ignore-unknown-features --features libm --exclude-features ${{ env.FEATURES_DEPENDING_ON_STD }} --target x86_64-unknown-none -- -D warnings
 
+      - name: cargo clippy (no_std 32bit)
+        run: cargo hack clippy --workspace --locked --optional-deps --each-feature --ignore-unknown-features --features libm --exclude-features ${{ env.FEATURES_DEPENDING_ON_STD }} --target thumbv8m.main-none-eabihf -- -D warnings
+
       - name: cargo clippy
         run: cargo hack clippy --workspace --locked --optional-deps --each-feature --ignore-unknown-features --features std -- -D warnings
 
@@ -213,7 +216,7 @@ jobs:
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ env.RUST_MIN_VER }}
-          targets: x86_64-unknown-none
+          targets: x86_64-unknown-none,thumbv8m.main-none-eabihf
 
       - name: install cargo-hack
         uses: taiki-e/install-action@v2
@@ -228,6 +231,9 @@ jobs:
       - name: cargo check (no_std)
         run: cargo hack check ${{ env.RUST_MIN_VER_PKGS }} --locked --optional-deps --each-feature --ignore-unknown-features --features libm --exclude-features ${{ env.FEATURES_DEPENDING_ON_STD }} --target x86_64-unknown-none
 
+      - name: cargo check (no_std 32bit)
+        run: cargo hack check ${{ env.RUST_MIN_VER_PKGS }} --locked --optional-deps --each-feature --ignore-unknown-features --features libm --exclude-features ${{ env.FEATURES_DEPENDING_ON_STD }} --target thumbv8m.main-none-eabihf
+
       - name: cargo check
         run: cargo hack check ${{ env.RUST_MIN_VER_PKGS }} --locked --optional-deps --each-feature --ignore-unknown-features --features std
 

src/blob.rs

@@ -2,12 +2,17 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use core::fmt;
-use core::sync::atomic::{AtomicU64, Ordering};
+use core::sync::atomic::Ordering;
 extern crate alloc;
 use alloc::boxed::Box;
 use alloc::sync::{Arc, Weak};
 use alloc::vec::Vec;
 
+#[cfg(not(target_has_atomic = "64"))]
+use core::sync::atomic::AtomicU32 as AtomicCounter;
+#[cfg(target_has_atomic = "64")]
+use core::sync::atomic::AtomicU64 as AtomicCounter;
+
 /// Shared data with an associated unique identifier.
 pub struct Blob<T> {
     data: Arc<dyn AsRef<[T]> + Send + Sync>,
@@ -82,15 +87,18 @@ where
     }
 }
 
-static ID_COUNTER: AtomicU64 = AtomicU64::new(0);
+static ID_COUNTER: AtomicCounter = AtomicCounter::new(0);
 
 impl<T> Blob<T> {
     /// Creates a new blob from the given data and generates a unique
     /// identifier.
     pub fn new(data: Arc<dyn AsRef<[T]> + Send + Sync>) -> Self {
         Self {
             data,
-            id: ID_COUNTER.fetch_add(1, Ordering::Relaxed),
+            #[allow(clippy::useless_conversion)] // Conversion is not useless on 32-bit platforms and is harmless on 64-bit platforms
+            // Overflow: We expect running this code on 32-bit targets to be rare enough in practise that we don't handle overflow.
+            // Impossible on 64-bit as counter is only ever incremented by 1.
+            id: ID_COUNTER.fetch_add(1, Ordering::Relaxed).into(),
         }
     }