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- speed up the Hamming distance
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@ -138,27 +138,24 @@ Hamming::ResultType Hamming::operator()(const unsigned char* a, const unsigned c
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}
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else
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#endif
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//for portability just use unsigned long -- and use the __builtin_popcountl (see docs for __builtin_popcountl)
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//as opposed to size_t -- TODO smart switching, if the size_t is a 64bits, use __builtin_popcountll
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typedef unsigned long pop_t;
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size_t i;
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//for portability just use unsigned long -- and use the __builtin_popcountll (see docs for __builtin_popcountll)
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typedef unsigned long long pop_t;
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const size_t modulo = size % sizeof(pop_t);
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const size_t end = size - modulo;
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for (i = 0; i < end; i += sizeof(pop_t))
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{
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pop_t a2 = *reinterpret_cast<const pop_t*> (a + i);
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pop_t b2 = *reinterpret_cast<const pop_t*> (b + i);
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result += __builtin_popcountl(a2 ^ b2);
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}
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const pop_t * a2 = reinterpret_cast<const pop_t*> (a);
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const pop_t * b2 = reinterpret_cast<const pop_t*> (b);
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const pop_t * a2_end = a2 + (size/sizeof(pop_t));
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for (; a2 != a2_end; ++a2, ++b2)
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result += __builtin_popcountll((*a2) ^ (*b2));
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if (modulo)
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{
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//in the case where size is not divisible by sizeof(size_t)
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//need to mask of the bits at the end
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pop_t a2=0,b2=0;
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memcpy(&a2,a+end,modulo);
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memcpy(&b2,b+end,modulo);
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//std::cout << std::hex << (a2^b2) << std::endl;
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result += __builtin_popcountl(a2 ^ b2);
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//need to mask off the bits at the end
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pop_t a_final=0,b_final=0;
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memcpy(&a_final,a2,modulo);
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memcpy(&b_final,b2,modulo);
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result += __builtin_popcountll(a_final ^ b_final);
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}
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return result;
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#else
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