table_lookup

fn table_lookup(table: *align(64) const [4][256]u32, idx0: u8, idx1: u8, idx2: u8, idx3: u8) [4]u32

File

Code

fn table_lookup(table: *align(64) const [4][256]u32, idx0: u8, idx1: u8, idx2: u8, idx3: u8) [4]u32 {
    if (side_channels_mitigations == .none) {
        return [4]u32{
            table[0][idx0],
            table[1][idx1],
            table[2][idx2],
            table[3][idx3],
        };
    } else {
        const table_len: usize = 256;
        const stride = switch (side_channels_mitigations) {
            .none => unreachable,
            .basic => table_len / 4,
            .medium => @max(1, @min(table_len, 2 * cache_line_bytes / 4)),
            .full => @max(1, @min(table_len, cache_line_bytes / 4)),
        };
        const of0 = idx0 % stride;
        const of1 = idx1 % stride;
        const of2 = idx2 % stride;
        const of3 = idx3 % stride;
        var t: [4][table_len / stride]u32 align(64) = undefined;
        var i: usize = 0;
        while (i < t[0].len) : (i += 1) {
            const tx = table[0][i * stride ..];
            t[0][i] = tx[of0];
            t[1][i] = tx[of1];
            t[2][i] = tx[of2];
            t[3][i] = tx[of3];
        }
        std.mem.doNotOptimizeAway(t);
        return [4]u32{
            t[0][idx0 / stride],
            math.rotl(u32, (&t[1])[idx1 / stride], 8),
            math.rotl(u32, (&t[2])[idx2 / stride], 16),
            math.rotl(u32, (&t[3])[idx3 / stride], 24),
        };
    }
}