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extern/draco/dracoenc/src/draco/core/math_utils.h
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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> | |||||
| #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_ | |||||