freb method
Implementation
Map<String,dynamic> freb(List eb, int start) {
u16 b = u16(31);
for (int i = 0; i < 31; ++i) {
b[i] = start += 1 << eb[i - 1];
}
// numbers here are at max 18 bits
i32 r = i32(b[30]);
for (int i = 1; i < 30; ++i) {
for (int j = b[i]; j < b[i + 1]; ++j) {
r[j] = ((j - b[i]) << 5) | i;
}
}
return { 'b': b, 'r': r };
}