Implement ConditionallySelectable trait for arrays

Author: Denis Varlakov

fuzz/Cargo.toml

@@ -33,3 +33,7 @@ path = "fuzzers/conditional_assign_i8.rs"
 [[bin]]
 name = "conditional_assign_i128"
 path = "fuzzers/conditional_assign_i128.rs"
+
+[[bin]]
+name = "conditional_assign_array"
+path = "fuzzers/conditional_assign_array.rs"

fuzz/fuzzers/conditional_assign_array.rs

@@ -0,0 +1,29 @@
+#![no_main]
+
+#[macro_use]
+extern crate libfuzzer_sys;
+extern crate subtle;
+extern crate core;
+
+use core::convert::TryFrom;
+
+use subtle::ConditionallySelectable;
+
+fuzz_target!(|data: &[u8]| {
+    let chunk_size: usize = 16;
+
+    if data.len() % chunk_size != 0 {
+        return;
+    }
+
+    for bytes in data.chunks(chunk_size) {
+        let mut x = [0u8; 16];
+        let y = <[u8; 16]>::try_from(bytes).unwrap();
+
+        x.conditional_assign(&y, 0.into());
+        assert_eq!(x, [0u8; 16]);
+
+        x.conditional_assign(&y, 1.into());
+        assert_eq!(x, y);
+    }
+});

src/lib.rs

@@ -55,7 +55,7 @@
 //!
 //! ## Minimum Supported Rust Version
 //!
-//! Rust **1.41** or higher.
+//! Rust **1.51** or higher.
 //!
 //! Minimum supported Rust version can be changed in the future, but it will be done with a minor version bump.
 //!
@@ -539,6 +539,23 @@ impl ConditionallySelectable for Choice {
     }
 }
 
+impl<T, const N: usize> ConditionallySelectable for [T; N]
+where T: ConditionallySelectable
+{
+    #[inline]
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        let mut output = *a;
+        output.conditional_assign(b, choice);
+        output
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
+        for (a_i, b_i) in self.iter_mut().zip(other) {
+            a_i.conditional_assign(b_i, choice)
+        }
+    }
+}
+
 /// A type which can be conditionally negated in constant time.
 ///
 /// # Note