Make use of intrinsics a feature-flag

CHANGELOG.md

@@ -7,9 +7,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+
 - Add `malloc` feature flag. It allows `littlefs` to link to `malloc` and `free` instead of relying on the caller to allocate memory ([#9])
+- Add a `software-intrinsics` feature flag, to disable the use of compiler intrinsics when compiling littlefs ([#12][])
+
+# Changed
+
 - upgrade `bindgen` to 0.69.4 and limit symbols to those prefixed with `lfs_` and `LFS_` ([#10])
 
+[#10]: https://github.com/trussed-dev/littlefs2-sys/pull/10
+[#12]: https://github.com/trussed-dev/littlefs2-sys/pull/12
+
 ## [0.1.7] - 2022-01-26
 
 ### Fixed

Cargo.toml

@@ -19,4 +19,5 @@ cc = "1"
 [features]
 assertions = []
 trace = []
-malloc = []
+malloc = []
+software-intrinsics = []

build.rs

@@ -11,8 +11,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .flag("-DLFS_NO_ERROR")
         .file("littlefs/lfs.c")
         .file("littlefs/lfs_util.c")
-        .file("string.c")
-    ;
+        .file("string.c");
+
+    #[cfg(feature = "software-intrinsics")]
+    let builder = builder.flag("-DLFS_NO_INTRINSICS");
 
     #[cfg(not(feature = "assertions"))]
     let builder = builder.flag("-DLFS_NO_ASSERT");