Salsa

pub fn Salsa(comptime rounds: comptime_int) type {
    return struct {
        /// Nonce length in bytes.
        pub const nonce_length = 8;
        /// Key length in bytes.
        pub const key_length = 32;

        /// Add the output of the Salsa stream cipher to `in` and stores the result into `out`.
        /// WARNING: This function doesn't provide authenticated encryption.
        /// Using the AEAD or one of the `box` versions is usually preferred.
        pub fn xor(out: []u8, in: []const u8, counter: u64, key: [key_length]u8, nonce: [nonce_length]u8) void {
            debug.assert(in.len == out.len);

            var d: [4]u32 = undefined;
            d[0] = mem.readInt(u32, nonce[0..4], .little);
            d[1] = mem.readInt(u32, nonce[4..8], .little);
            d[2] = @as(u32, @truncate(counter));
            d[3] = @as(u32, @truncate(counter >> 32));
            SalsaImpl(rounds).salsaXor(out, in, keyToWords(key), d);
        }
    };
}