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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#include "binary_hamming_distance.h"
#include <cstdint>
namespace vespalib {
size_t binary_hamming_distance(const void *lhs, const void *rhs, size_t sz) {
uintptr_t addr_a = (uintptr_t) lhs;
uintptr_t addr_b = (uintptr_t) rhs;
size_t sum = 0;
size_t i = 0;
static_assert(sizeof(uint64_t) == 8);
bool aligned = ((addr_a & 0x7) == 0) && ((addr_b & 0x7) == 0);
if (__builtin_expect(aligned, true)) {
const uint64_t *words_a = static_cast<const uint64_t *>(lhs);
const uint64_t *words_b = static_cast<const uint64_t *>(rhs);
for (; i * 8 + 7 < sz; ++i) {
uint64_t xor_bits = words_a[i] ^ words_b[i];
sum += __builtin_popcountl(xor_bits);
}
}
if (__builtin_expect((i * 8 < sz), false)) {
const uint8_t *bytes_a = static_cast<const uint8_t *>(lhs);
const uint8_t *bytes_b = static_cast<const uint8_t *>(rhs);
for (i *= 8; i < sz; ++i) {
uint64_t xor_bits = bytes_a[i] ^ bytes_b[i];
sum += __builtin_popcountl(xor_bits);
}
}
return sum;
};
}
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