static void hid_keyboard_process_keycode(HIDState *hs)
{
    uint8_t hid_code, index, key;
    int i, keycode, slot;

    if (hs->n == 0) {
        return;
    }
    slot = hs->head & QUEUE_MASK; QUEUE_INCR(hs->head); hs->n--;
    keycode = hs->kbd.keycodes[slot];

    if (!hs->n) {
        trace_hid_kbd_queue_empty();
    }

    key = keycode & 0x7f;
    index = key | ((hs->kbd.modifiers & (1 << 8)) >> 1);
    hid_code = hid_usage_keys[index];
    hs->kbd.modifiers &= ~(1 << 8);

    switch (hid_code) {
    case 0x00:
        return;

    case 0xe0:
        assert(key == 0x1d);
        if (hs->kbd.modifiers & (1 << 9)) {
            /* The hid_codes for the 0xe1/0x1d scancode sequence are 0xe9/0xe0.
             * Here we're processing the second hid_code.  By dropping bit 9
             * and setting bit 8, the scancode after 0x1d will access the
             * second half of the table.
             */
            hs->kbd.modifiers ^= (1 << 8) | (1 << 9);
            return;
        }
        /* fall through to process Ctrl_L */
    case 0xe1 ... 0xe7:
        /* Ctrl_L/Ctrl_R, Shift_L/Shift_R, Alt_L/Alt_R, Win_L/Win_R.
         * Handle releases here, or fall through to process presses.
         */
        if (keycode & (1 << 7)) {
            hs->kbd.modifiers &= ~(1 << (hid_code & 0x0f));
            return;
        }
        /* fall through */
    case 0xe8 ... 0xe9:
        /* USB modifiers are just 1 byte long.  Bits 8 and 9 of
         * hs->kbd.modifiers implement a state machine that detects the
         * 0xe0 and 0xe1/0x1d sequences.  These bits do not follow the
         * usual rules where bit 7 marks released keys; they are cleared
         * elsewhere in the function as the state machine dictates.
         */
        hs->kbd.modifiers |= 1 << (hid_code & 0x0f);
        return;

    case 0xea ... 0xef:
        abort();

    default:
        break;
    }

    if (keycode & (1 << 7)) {
        for (i = hs->kbd.keys - 1; i >= 0; i--) {
            if (hs->kbd.key[i] == hid_code) {
                hs->kbd.key[i] = hs->kbd.key[-- hs->kbd.keys];
                hs->kbd.key[hs->kbd.keys] = 0x00;
                break;
            }
        }
        if (i < 0) {
            return;
        }
    } else {
        for (i = hs->kbd.keys - 1; i >= 0; i--) {
            if (hs->kbd.key[i] == hid_code) {
                break;
            }
        }
        if (i < 0) {
            if (hs->kbd.keys < sizeof(hs->kbd.key)) {
                hs->kbd.key[hs->kbd.keys++] = hid_code;
            }
        } else {
            return;
        }
    }
}
Unknown