29 lines
775 B
C++
29 lines
775 B
C++
#include <mbgl/math/log2.hpp>
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namespace mbgl {
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namespace util {
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// From http://stackoverflow.com/questions/3272424/compute-fast-log-base-2-ceiling
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uint32_t ceil_log2(uint64_t x) {
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static const uint64_t t[6] = {0xFFFFFFFF00000000,
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0x00000000FFFF0000,
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0x000000000000FF00,
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0x00000000000000F0,
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0x000000000000000C,
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0x0000000000000002};
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uint32_t y = (((x & (x - 1)) == 0) ? 0 : 1);
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uint32_t j = 32;
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for (const auto& i : t) {
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const uint32_t k = (((x & i) == 0) ? 0 : j);
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y += k;
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x >>= k;
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j >>= 1;
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}
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return y;
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}
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} // namespace util
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} // namespace mbgl
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