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the general idea is:

1. bitwise shift to the right
2. xor with original value, so only transition bits are left
3. count remaining bits

here's a demo implementation, using std::bitset (for demo purpose), same idea works with uints, too, ofc.

#include <bitset>
bitset<24> a("00001111100000111100000");
// 000001111100000111100000
auto b = a >> 1;
// 000000111110000011110000
auto c = a ^ b;
// 000001000010000100010000
auto len = c.count();  // popcnt() , if you use integers.
// 4