Andrei Alexandrescu wrote:
> On 04/10/2010 01:55 PM, Rainer Deyke wrote:
>> On 4/10/2010 11:52, Andrei Alexandrescu wrote:
>>> I think this would work:
>>>
>>> uint maxOR(uint maxa, uint maxb) {
>>> if (maxa< maxb) return maxOR(maxb, maxa);
>>> uint candidate = 0;
>>> foreach (i, bit; byBitDescending(maxa)) {
>>> if (bit) continue;
>>> auto t = candidate | (1<< (31 - i));
>>> if (t<= maxb) candidate = t;
>>> }
>>> return maxa | candidate;
>>> }
>>
>> This looks wrong. Your function, if I understand it correctly, flips
>> all the bits in 'maxb' (excluding the leading zeros).
>
> It tries to set all bits in which maxa is zero starting and keeps them
> set if the resulting number is less than maxb.
>
In other words: maxa | ((1 << highbit (maxb))-1) where:
int highbit (uint n) {
auto result = 0;
if (n & 0xFFFF0000) {
result += 16;
n = n >> 16;
}
if (n & 0xFF00) {
result += 8;
n = n >> 8;
}
if (n & 0xF0) {
result += 4;
n = n >> 4;
}
if (n & 0xC) {
result += 2;
n = n >> 2;
}
if (n & 0x2) {
result += 1;
n = n >> 1;
}
if (n & 0x1) {
result += 1;
}
return result;
}
Jerome
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