We need to count a number of transitions in a bit string from 0->1 and 1->0. I needed this in order to determine Uniform Descriptor in Local Binary Patterns(LBP)
Samples
0000 0000 (0 Transitions : Uniform) 0x0 1110 0011 (2 Transitions : Uniform) 0xE3 0101 0000 (4 Transitions : NonUniform) 0x50 0000 1010 (4 Transitions : NonUniform) 0xA 0000 1001 (3 Transitions : NonUniform) 0x9
Sample run (0xE3)
0x e3 : 227 :: 00000000000000000000000011100011 0x 71 : 113 :: 00000000000000000000000001110001 0x 92 : 146 :: 00000000000000000000000010010010 Transition : 3
Implemenation
We are going to shift the value to the right and then XOR it with the original value to get the number of transitions. From there we going to use population count to get the count of the on bits.
XOR Truth table
INPUT OUTPUT ----------------------- A B A XOR B 0 0 0 0 1 1 1 0 1 1 1 0
template void bitstr(const T& out) noexcept;
template int popcnt(const T& val) noexcept;
int main()
{
// Uniform descriptors
// 0000 0000 (0 Transitions : Uniform) 0x0
// 1110 0011 (2 Transitions : Uniform) 0xE3
// 0101 0000 (4 Transitions : NonUniform) 0x50
// 0000 1010 (4 Transitions : NonUniform) 0xA
// 0000 1001 (3 Transitions : NonUniform) 0x9
int a = 0xE3;
int b = a >> 1;
int c = a ^ b;
int count = popcnt(c);
bitstr(a);
bitstr(b);
bitstr(c);
std::cout << "Transition : " <<count; return="" 0;="" }="" template="" <class="" t="">
int popcnt(const T& val) noexcept
{
int bitcount;
__asm__ ("popcnt %1, %1" : "=r" (bitcount) : "0" (val));
return bitcount;
}
template
void bitstr(const T& out) noexcept
{
std::bitset bs(out);
auto val = static_cast(out);
std::cout << "0x"
<< std::setw(8) << std::hex << val << " : "
<< std::setw(8) << std::dec << val<< " :: " << bs << std::endl;
}
</count;>