fastmath.hpp

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/*******************************************************************************
* Copyright (c) 2022-2023 Intel Corporation
*
* 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.
*******************************************************************************/
 
 
#pragma once
 
#include "common/utils/common.hpp"
 
namespace gpu::xetla {
 
inline int clz(int x) {
 
    for (int i = 31; i >= 0; i--) {
 
        if ((1 << i) & x) { return (31 - i); }
    }
    return 32;
}
 
inline int find_log2(int x) {
 
    int a = int(31 - clz(x));
    a = a + ((x & (x - 1)) != 0);
    return a;
}
 
struct FastDivMod {
 
    int divisor;
    unsigned int multiplier;
    unsigned int shift_right;
 
    inline FastDivMod() : divisor(0), multiplier(0), shift_right(0) {}
 
    inline FastDivMod(int divisor_) : divisor(divisor_) {
 
        if (divisor != 1) {
            unsigned int p = 31 + find_log2(divisor);
            unsigned m = unsigned(
                    ((1ull << p) + unsigned(divisor) - 1) / unsigned(divisor));
 
            multiplier = m;
            shift_right = p - 32;
        } else {
 
            multiplier = 0;
            shift_right = 0;
        }
    }
 
    operator int() const { return divisor; }
 
    __XETLA_API KERNEL_FUNC void fast_divmod(
            int &quotient, int &remainder, int dividend) const {
 
        int lo_part;
        quotient = (divisor != 1)
                ? __ESIMD_ENS::imul(lo_part, dividend, multiplier)
                        >> shift_right
                : dividend;
 
        remainder = dividend - (quotient * divisor);
    }
 
    __XETLA_API KERNEL_FUNC int div(int dividend) const {
 
        int quotient, remainder;
        fast_divmod(quotient, remainder, dividend);
        return quotient;
    }
};
 
} // namespace gpu::xetla