💿🐜 Antkeeper source code
https://antkeeper.com
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244 lines
7.6 KiB
244 lines
7.6 KiB
/*
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* Copyright (C) 2021 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "resource-loader.hpp"
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#include "physics/orbit/ephemeris.hpp"
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#include "utility/bit-math.hpp"
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#include <cstdint>
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#include <physfs.h>
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/// Offset to time data in the JPL DE header, in bytes.
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static constexpr std::size_t jpl_de_offset_time = 0xA5C;
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/// Offset to the first coefficient table in the JPL DE header, in bytes.
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static constexpr std::size_t jpl_de_offset_table1 = 0xA88;
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/// Offset to the DE version number in the JPL DE header, in bytes.
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static constexpr std::size_t jpl_de_offset_denum = 0xB18;
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/// Offset to the second coefficient table in the JPL DE header, in bytes.
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static constexpr std::size_t jpl_de_offset_table2 = 0xB1C;
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/// Offset to the third coefficient table in the JPL DE header, in bytes, if the constant limit has not been exceeded.
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static constexpr std::size_t jpl_de_offset_table3 = 0xB28;
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/// Mask to detect bytes in the most significant word of the JPL DE version number.
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static constexpr std::int32_t jpl_de_denum_endian_mask = 0xFFFF0000;
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/// Number of items in the first coefficient table.
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static constexpr std::size_t jpl_de_table1_count = 12;
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/// Number of items in the second coefficient table.
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static constexpr std::size_t jpl_de_table2_count = 1;
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/// Number of items in the third coefficient table.
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static constexpr std::size_t jpl_de_table3_count = 2;
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/// Maximum number of items in a JPL DE file.
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static constexpr std::size_t jpl_de_max_item_count = jpl_de_table1_count + jpl_de_table2_count + jpl_de_table3_count;
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/// Maximum number of constants in the first set of constant names.
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static constexpr std::size_t jpl_de_constant_limit = 400;
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/// Length of a constant name, in bytes.
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static constexpr std::size_t jpl_de_constant_length = 6;
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/// Enumerated IDs of the JPL DE items.
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enum
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{
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/// Mercury
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jpl_de_id_mercury,
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/// Venus
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jpl_de_id_venus,
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/// Earth-Moon barycenter
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jpl_de_id_embary,
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/// Mars
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jpl_de_id_mars,
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/// Jupiter
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jpl_de_id_jupiter,
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/// Saturn
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jpl_de_id_saturn,
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/// Uranus
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jpl_de_id_uranus,
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/// Neptune
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jpl_de_id_neptune,
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/// Pluto
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jpl_de_id_pluto,
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/// Moon
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jpl_de_id_moon,
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/// Sun
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jpl_de_id_sun,
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/// Earth nutation
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jpl_de_id_earth_nutation,
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/// Lunar mantle libration
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jpl_de_id_luma_libration,
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/// Lunar mantle angular velocity
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jpl_de_id_luma_angular_velocity,
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/// TT-TDB
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jpl_de_id_tt_tdb
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};
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/// Number of components for each JPL DE item.
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static constexpr std::size_t jpl_de_component_count[jpl_de_max_item_count] =
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{
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3, // Mercury: x,y,z (km)
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3, // Venus: x,y,z (km)
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3, // Earth-Moon barycenter: x,y,z (km)
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3, // Mars: x,y,z (km)
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3, // Jupiter: x,y,z (km)
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3, // Saturn: x,y,z (km)
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3, // Uranus: x,y,z (km)
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3, // Neptune: x,y,z (km)
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3, // Pluto: x,y,z (km)
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3, // Moon: x,y,z (km)
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3, // Sun: x,y,z (km)
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2, // Earth nutation: d_psi,d_epsilon (radians)
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3, // Lunar mantle libration: phi,theta,ps (radians)
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3, // Lunar mantle angular velocity: omega_x,omega_y,omega_z (radians/day)
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1 // TT-TDB: t (seconds)
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};
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/// Reads and swaps the byte order of 32-bit numbers.
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static PHYSFS_sint64 read_swap32(PHYSFS_File* handle, void* buffer, PHYSFS_uint64 len)
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{
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PHYSFS_sint64 status = PHYSFS_readBytes(handle, buffer, len);
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for (std::uint32_t* ptr32 = (uint32_t*)buffer; len >= 8; len -= 8, ++ptr32)
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*ptr32 = bit::swap32(*ptr32);
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return status;
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}
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/// Reads and swaps the byte order of 64-bit numbers.
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static PHYSFS_sint64 read_swap64(PHYSFS_File* handle, void* buffer, PHYSFS_uint64 len)
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{
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PHYSFS_sint64 status = PHYSFS_readBytes(handle, buffer, len);
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for (std::uint64_t* ptr64 = (uint64_t*)buffer; len >= 8; len -= 8, ++ptr64)
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*ptr64 = bit::swap64(*ptr64);
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return status;
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}
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template <>
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physics::orbit::ephemeris<double>* resource_loader<physics::orbit::ephemeris<double>>::load(resource_manager* resource_manager, PHYSFS_File* file, const std::filesystem::path& path)
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{
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// Init file reading function pointers
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PHYSFS_sint64 (*read32)(PHYSFS_File*, void*, PHYSFS_uint64) = &PHYSFS_readBytes;
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PHYSFS_sint64 (*read64)(PHYSFS_File*, void*, PHYSFS_uint64) = &PHYSFS_readBytes;
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// Read DE version number
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std::int32_t denum;
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PHYSFS_seek(file, jpl_de_offset_denum);
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PHYSFS_readBytes(file, &denum, sizeof(std::int32_t));
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// If file endianness does not match host
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if (denum & jpl_de_denum_endian_mask)
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{
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// Use endian-swapping read functions
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read32 = &read_swap32;
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read64 = &read_swap64;
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}
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// Read ephemeris time
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double ephemeris_time[3];
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PHYSFS_seek(file, jpl_de_offset_time);
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read64(file, ephemeris_time, sizeof(double) * 3);
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// Make time relative to J2000 epoch
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const double epoch = 2451545.0;
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ephemeris_time[0] -= epoch;
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ephemeris_time[1] -= epoch;
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// Read number of constants
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std::int32_t constant_count;
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read32(file, &constant_count, sizeof(std::int32_t));
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// Read first coefficient table
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std::int32_t coeff_table[jpl_de_max_item_count][3];
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PHYSFS_seek(file, jpl_de_offset_table1);
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read32(file, coeff_table, sizeof(std::int32_t) * jpl_de_table1_count * 3);
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// Read second coefficient table
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PHYSFS_seek(file, jpl_de_offset_table2);
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read32(file, &coeff_table[jpl_de_table1_count][0], sizeof(std::int32_t) * jpl_de_table2_count * 3);
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// Seek past extra constant names
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if (constant_count > jpl_de_constant_limit)
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PHYSFS_seek(file, jpl_de_offset_table3 + (constant_count - jpl_de_constant_limit) * jpl_de_constant_length);
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// Read third coefficient table
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read32(file, &coeff_table[jpl_de_table1_count + jpl_de_table2_count][0], sizeof(std::int32_t) * jpl_de_table3_count * 3);
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// Calculate number of coefficients per record
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std::int32_t record_coeff_count = 0;
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for (int i = 0; i < jpl_de_max_item_count; ++i)
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{
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std::int32_t coeff_count = coeff_table[i][0] + coeff_table[i][1] * coeff_table[i][2] * jpl_de_component_count[i] - 1;
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record_coeff_count = std::max(record_coeff_count, coeff_count);
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}
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// Calculate record size and record count
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std::size_t record_size = record_coeff_count * sizeof(double);
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std::size_t record_count = static_cast<std::size_t>((ephemeris_time[1] - ephemeris_time[0]) / ephemeris_time[2]);
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// Calculate coefficient strides
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std::size_t strides[11];
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for (int i = 0; i < 11; ++i)
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strides[i] = coeff_table[i][2] * coeff_table[i][1] * 3;
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// Allocate and resize ephemeris to accommodate items 0-10
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physics::orbit::ephemeris<double>* ephemeris = new physics::orbit::ephemeris<double>();
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ephemeris->resize(11);
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// Init trajectories
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for (int i = 0; i < 11; ++i)
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{
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auto& trajectory = (*ephemeris)[i];
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trajectory.t0 = ephemeris_time[0];
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trajectory.t1 = ephemeris_time[1];
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trajectory.dt = ephemeris_time[2] / static_cast<double>(coeff_table[i][2]);
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trajectory.n = coeff_table[i][1];
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trajectory.a.resize(record_count * strides[i]);
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}
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// Read coefficients
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for (std::size_t i = 0; i < record_count; ++i)
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{
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// Seek to coefficient record
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PHYSFS_seek(file, (i + 2) * record_size + 2 * sizeof(double));
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for (int j = 0; j < 11; ++j)
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{
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read64(file, &(*ephemeris)[j].a[i * strides[j]], sizeof(double) * strides[j]);
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}
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}
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return ephemeris;
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}
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