mirror of https://github.com/ecmwf/eccodes.git
75 lines
2.2 KiB
C++
75 lines
2.2 KiB
C++
/*
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* (C) Copyright 2005- ECMWF.
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*
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* This software is licensed under the terms of the Apache Licence Version 2.0
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* which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
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*
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* In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
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* virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
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*/
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#pragma once
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#include "grib_scaling.h"
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#include <array>
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#include <type_traits>
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#include <cstdint>
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/**
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.. _init_ieee_table:
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Init IBM Floats Table
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=====================
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Initializes the ibm_table with IBM Float values. Nearest smaller values (e.g., reference values for grid_simple) are taken from this table.
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Details
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-------
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The table layout is as follows:
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+-------+----------------+------------------------+
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| idx (i) | multiplier (e) | value (v = mmin * e) |
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+-------+----------------+------------------------+
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| 0 | 16^(-70) | 0x100000 * 2^(-70) |
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| 1 | 16^(-69) | 0x100000 * 2^(-69) |
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| ... | ... | ... |
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| 126 | 16^56 | 0x100000 * 2^56 |
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| 127 | 16^57 | 0x100000 * 2^57 |
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+-------+----------------+------------------------+
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The vmin and vmax boundaries are defined as:
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- vmin = 0x100000 * 2^(-70)
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- vmax = 0xffffff * 2^57
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*/
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struct IbmTable {
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private:
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using ValueType = double;
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static constexpr int TABLESIZE = 128;
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static constexpr uint32_t mantissa_min = 0x100000;
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static constexpr uint32_t mantissa_max = 0xffffff;
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public:
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static constexpr std::array<ValueType, TABLESIZE> e = []() {
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std::array<ValueType, TABLESIZE> multiplier{};
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multiplier[0] = 0;
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for (int i = 0; i < TABLESIZE; ++i) {
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multiplier[i] = codes_power<ValueType>(i - 70, 16);
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}
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return multiplier;
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}();
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static constexpr std::array<ValueType, TABLESIZE> v = []() {
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std::array<ValueType, TABLESIZE> values{};
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values[0] = 0;
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for (int i = 0; i < TABLESIZE; ++i) {
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values[i] = e[i] * mantissa_min;
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}
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return values;
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}();
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static constexpr ValueType vmin = e[0] * mantissa_min;
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static constexpr ValueType vmax = e[127] * mantissa_max;
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};
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