o3d/base/cross/bits.h

/*
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 * in the documentation and/or other materials provided with the
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 *
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// This file defines some bit utilities.

#ifndef O3D_BASE_CROSS_BITS_H_
#define O3D_BASE_CROSS_BITS_H_

#include "base/logging.h"

namespace o3d {
namespace base {
namespace bits {

// Returns the integer i such as 2^i <= n < 2^(i+1)
static inline int Log2Floor(unsigned int n) {
  if (n == 0)
    return -1;
  int log = 0;
  unsigned int value = n;
  for (int i = 4; i >= 0; --i) {
    int shift = (1 << i);
    unsigned int x = value >> shift;
    if (x != 0) {
      value = x;
      log += shift;
    }
  }
  DCHECK_EQ(value, 1u);
  return log;
}

// Returns the integer i such as 2^(i-1) < n <= 2^i
static inline int Log2Ceiling(unsigned int n) {
  if (n == 0) {
    return -1;
  } else {
    // Log2Floor returns -1 for 0, so the following works correctly for n=1.
    return 1 + Log2Floor(n - 1);
  }
}

}  // namespace bits
}  // namespace base
}  // namespace o3d

#endif  // O3D_BASE_CROSS_BITS_H_