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+// Copyright 2016 The Draco Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef DRACO_CORE_MATH_UTILS_H_
+#define DRACO_CORE_MATH_UTILS_H_
+
+#include <inttypes.h>
+
+#include "draco/core/vector_d.h"
+
+#define DRACO_INCREMENT_MOD(I, M) (((I) == ((M)-1)) ? 0 : ((I) + 1))
+
+// Returns floor(sqrt(x)) where x is an integer number. The main intend of this
+// function is to provide a cross platform and deterministic implementation of
+// square root for integer numbers. This function is not intended to be a
+// replacement for std::sqrt() for general cases. IntSqrt is in fact about 3X
+// slower compared to most implementation of std::sqrt().
+inline uint64_t IntSqrt(uint64_t number) {
+  if (number == 0) {
+    return 0;
+  }
+  // First estimate good initial value of the square root as log2(number).
+  uint64_t act_number = number;
+  uint64_t square_root = 1;
+  while (act_number >= 2) {
+    // Double the square root until |square_root * square_root > number|.
+    square_root *= 2;
+    act_number /= 4;
+  }
+  // Perform Newton's (or Babylonian) method to find the true floor(sqrt()).
+  do {
+    // New |square_root| estimate is computed as the average between
+    // |square_root| and |number / square_root|.
+    square_root = (square_root + number / square_root) / 2;
+
+    // Note that after the first iteration, the estimate is always going to be
+    // larger or equal to the true square root value. Therefore to check
+    // convergence, we can simply detect condition when the square of the
+    // estimated square root is larger than the input.
+  } while (square_root * square_root > number);
+  return square_root;
+}
+
+#endif  // DRACO_CORE_MATH_UTILS_H_