[core] Moved util::log2 to its own header

- Added util::{MIN,MAX}_ZOOM_F to avoid consecutive conversions from
double to float
- Move util::log2 to its own header (part of mbgl/math)

1 files changed, 27 insertions, 0 deletions

diff --git a/include/mbgl/math/log2.hpp b/include/mbgl/math/log2.hpp
new file mode 100644
index 0000000000..8a3bc7f1c0
--- /dev/null
+++ b/include/mbgl/math/log2.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <cmath>
+#include <cstdint>
+#include <type_traits>
+
+namespace mbgl {
+namespace util {
+
+// Computes the log2(x) rounded up to the next integer.
+// (== number of bits required to store x)
+uint32_t ceil_log2(uint64_t x);
+
+template <typename T>
+typename std::enable_if_t<std::is_floating_point<T>::value, T> log2(T x)
+{
+// log2() is producing wrong results on ARMv5 binaries
+// running on ARMv7+ CPUs.
+#if defined(__ANDROID__)
+    return std::log(x) / M_LN2;
+#else
+    return std::log2(x);
+#endif
+}
+
+} // namespace util
+} // namespace mbgl