8. Advanced: versioned packed SPVAR

Difficulty: Advanced

versioned-packed-spvar.gpc

define SAVE_MAGIC = 0x5A31;
define SAVE_VERSION = 1;

define MODE_SHIFT = 0;
define MODE_MASK = 0x00000003;
define ENABLE_SHIFT = 2;
define ENABLE_MASK = 0x00000004;
define STRENGTH_SHIFT = 3;
define STRENGTH_MASK = 0x000003F8;

int mode;
int enabled;
int strength = 25;
int packed;
int dirty;

init {
    if(get_pvar(SPVAR_1, 0, INT32_MAX, 0) == SAVE_MAGIC &&
       get_pvar(SPVAR_2, 0, 100, 0) == SAVE_VERSION) {
        packed = get_pvar(SPVAR_3, 0, 1023, 0);
        unpack_settings(packed);
    }
}

main {
    if(event_press(PS5_TRIANGLE)) {
        mode = mode + 1;
        if(mode > 3) mode = 0;
        dirty = TRUE;
    }

    if(event_press(PS5_CROSS)) {
        enabled = !enabled;
        dirty = TRUE;
    }

    if(event_press(PS5_UP)) {
        strength = strength + 1;
        if(strength > 100) strength = 100;
        dirty = TRUE;
    }

    if(dirty && event_press(PS5_OPTIONS)) {
        packed = pack_settings();
        set_pvar(SPVAR_1, SAVE_MAGIC);
        set_pvar(SPVAR_2, SAVE_VERSION);
        set_pvar(SPVAR_3, packed);
        dirty = FALSE;
    }

    set_val(TRACE_1, mode);
    set_val(TRACE_2, enabled);
    set_val(TRACE_3, strength);
}

function pack_settings() {
    int_dummy = 0;
    int_dummy = int_dummy | ((mode << MODE_SHIFT) & MODE_MASK);
    int_dummy = int_dummy | ((enabled << ENABLE_SHIFT) & ENABLE_MASK);
    int_dummy = int_dummy | ((strength << STRENGTH_SHIFT) & STRENGTH_MASK);
    return int_dummy;
}

function unpack_settings(value) {
    mode = (value & MODE_MASK) >> MODE_SHIFT;
    enabled = (value & ENABLE_MASK) >> ENABLE_SHIFT;
    strength = (value & STRENGTH_MASK) >> STRENGTH_SHIFT;

    if(mode < 0 || mode > 3) mode = 0;
    if(strength < 0 || strength > 100) strength = 25;
}

int int_dummy;

GPC permits top-level declarations later in the file, but production style should move int_dummy beside the other globals. It is shown here to reinforce that "top-level" matters more than textual position.

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What it teaches: magic/version, manual bit layout, identical pack/unpack schema, post-load validation.