| // Copyright (C) 2013 Davis E. King ([email protected]) | |
| // License: Boost Software License See LICENSE.txt for the full license. | |
| namespace dlib | |
| { | |
| // ---------------------------------------------------------------------------------------- | |
| template < | |
| typename T | |
| > | |
| T count_bits ( | |
| T v | |
| ) | |
| /*! | |
| requires | |
| - T is an unsigned integral type | |
| ensures | |
| - returns the number of bits in v which are set to 1. | |
| !*/ | |
| { | |
| COMPILE_TIME_ASSERT(is_unsigned_type<T>::value && sizeof(T) <= 8); | |
| // This bit of bit trickery is from: | |
| // http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSet64 | |
| v = v - ((v >> 1) & (T)~(T)0/3); | |
| v = (v & (T)~(T)0/15*3) + ((v >> 2) & (T)~(T)0/15*3); | |
| v = (v + (v >> 4)) & (T)~(T)0/255*15; | |
| return (T)(v * ((T)~(T)0/255)) >> (sizeof(T) - 1) * CHAR_BIT; | |
| } | |
| // ---------------------------------------------------------------------------------------- | |
| template < | |
| typename T | |
| > | |
| T hamming_distance ( | |
| const T& a, | |
| const T& b | |
| ) | |
| /*! | |
| requires | |
| - T is an unsigned integral type | |
| ensures | |
| - returns the number of bits which differ between a and b. | |
| !*/ | |
| { | |
| return count_bits(a^b); | |
| } | |
| // ---------------------------------------------------------------------------------------- | |
| template < | |
| typename T | |
| > | |
| T hamming_distance ( | |
| const std::pair<T,T>& a, | |
| const std::pair<T,T>& b | |
| ) | |
| /*! | |
| requires | |
| - T is an unsigned integral type or a std::pair that, recursively, eventually | |
| contains unsigned integral types. | |
| ensures | |
| - returns the number of bits which differ between a and b. | |
| !*/ | |
| { | |
| return hamming_distance(a.first,b.first) + hamming_distance(a.second, b.second); | |
| } | |
| // ---------------------------------------------------------------------------------------- | |
| } | |