function bisect_clear(a, b) {
    for (var j = a; j <= b; j++) {
    for (var i = 0; i < 16 * 4; i++) {
        var index = (i * 0x10000 + (i%16) * 0x1000 + 0x30 - 0x8) / 4;
        bigmem[j][index] = 0;