move a chunk of the README into CONTRIBUTING.md

library/compiler-builtins/libm/src/lib.rs

@@ -355,7 +355,7 @@ impl F32Ext for f32 {
     }
 }
 
-/// Math support for `f32`
+/// Math support for `f64`
 ///
 /// This trait is sealed and cannot be implemented outside of `libm`.
 pub trait F64Ext: private::Sealed {

library/compiler-builtins/libm/src/math/trunc.rs

@@ -22,3 +22,11 @@ pub fn trunc(x: f64) -> f64 {
     i &= !m;
     f64::from_bits(i)
 }
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn sanity_check() {
+        assert_eq!(super::trunc(1.1), 1.0);
+    }
+}

library/compiler-builtins/libm/src/math/truncf.rs

@@ -22,3 +22,11 @@ pub fn truncf(x: f32) -> f32 {
     i &= !m;
     f32::from_bits(i)
 }
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn sanity_check() {
+        assert_eq!(super::truncf(1.1), 1.0);
+    }
+}