/* ZUPT — Constant-Time MAC Comparison (Jasmin)
 * Copyright (c) 2026 Cristian Cezar Moisés
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * CT-REQUIRED: Timing independent of input byte values.
 * Compare 32 bytes as 4 × u64 — no byte-level access needed.
 */

export fn zupt_mac_verify_ct(
    reg u64 expected_ptr,
    reg u64 actual_ptr)
    -> reg u64
{
    reg u64 diff a b tmp;
    inline int i;

    diff = 0;

    /* 4 × 8 bytes = 32 bytes. u64 loads — no size mismatch. */
    for i = 0 to 4 {
        a = [expected_ptr + 8 * i];
        b = [actual_ptr + 8 * i];
        tmp = a;
        tmp ^= b;
        diff |= tmp;
    }

    return diff;
}