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#include <mbgl/util/math.hpp>
namespace mbgl {
namespace util {
// From http://stackoverflow.com/questions/3272424/compute-fast-log-base-2-ceiling
uint32_t ceil_log2(uint64_t x) {
static const uint64_t t[6] = {0xFFFFFFFF00000000, 0x00000000FFFF0000,
0x000000000000FF00, 0x00000000000000F0,
0x000000000000000C, 0x0000000000000002};
uint32_t y = (((x & (x - 1)) == 0) ? 0 : 1);
uint32_t j = 32;
for (const auto& i : t) {
const uint32_t k = (((x & i) == 0) ? 0 : j);
y += k;
x >>= k;
j >>= 1;
}
return y;
}
double log2(double x) {
// log2() is producing wrong results on ARMv5 binaries
// running on ARMv7+ CPUs.
#if defined(__ANDROID__)
return std::log(x) / 0.6931471805599453; // log(x) / log(2)
#else
return ::log2(x);
#endif
}
} // namespace util
} // namespace mbgl
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