log2_exp2.h

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/**
 *  Copyright (C) 2026 HJimmyK(Jericho Knox)
 *
 *  This file is part of LAMMP.
 *
 *  LAMMP is free software: you can redistribute it and/or modify it under
 *  the terms of the GNU Lesser General Public License (LGPL) as published
 *   by the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed WITHOUT ANY WARRANTY.
 *
 *  See <https://www.gnu.org/licenses/>.
 */
 
#ifndef __LAMMP_LOG2_EXP2_H__
#define __LAMMP_LOG2_EXP2_H__
 
#include <stdint.h>
 
/**
 * @brief floor(log2(1+x/B)*B), B=2^64
 * @param x 输入的小数部分
 * @return floor(log2(1+x/B)*B)
 */
uint64_t log2_fixed_64(uint64_t x);
 
/**
 * @brief floor(exp2(x/B)*B-B), B=2^64
 * @param x 输入的小数部分
 * @return floor(exp2(x/B)*B-B)
 */
uint64_t exp2_fixed_64(uint64_t x);
 
/**
 * @brief floor(log2(1+x/B)*B), B=2^128
 * @param high 输入的小数部分高64位
 * @param low 输入的小数部分低64位
 * @param dst 输出数组（2个元素）：dst[0] 为低64位，dst[1] 为高64位
 * @note x = high * 2^64 + low
 */
void log2_fixed_128(uint64_t* dst, uint64_t high, uint64_t low);
 
/**
 * @brief floor(exp2(x/B)*B-B), B=2^128
 * @param high 输入的小数部分高64位
 * @param low 输入的小数部分低64位
 * @param dst 输出数组（2个元素）：dst[0] 为低64位，dst[1] 为高64位
 * @note x = high * 2^64 + low
 */
void exp2_fixed_128(uint64_t* dst, uint64_t high, uint64_t low);
 
#endif // __LAMMP_LOG2_EXP2_H__