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/* Copyright 2019-2022 Axel Huebl
*
* This file is part of WarpX.
*
* License: BSD-3-Clause-LBNL
*/
#ifndef ABLASTR_INDEX_HANDLING_H
#define ABLASTR_INDEX_HANDLING_H
#include <cstdint>
namespace ablastr::particles {
/** A helper function to derive a globally unique particle ID
*
* @param[in] id AMReX particle ID (on local cpu/rank), AoS .id
* @param[in] cpu AMReX particle CPU (rank) at creation of the particle, AoS .cpu
* @return global particle ID that is unique and permanent in the whole simulation
*/
constexpr uint64_t
localIDtoGlobal (int const id, int const cpu)
{
static_assert(sizeof(int) * 2u <= sizeof(uint64_t),
"int size might cause collisions in global IDs");
// implementation:
// - we cast both 32-bit (or smaller) ints to a 64bit unsigned int
// - this will leave half of the "upper range" bits in the 64bit unsigned int zeroed out
// because the corresponding (extended) value range was not part of the value range in
// the int representation
// - we bit-shift the cpu into the upper half of zero bits in the 64 bit unsigned int
// (imagine this step as "adding a per-cpu/rank offset to the local integers")
// - then we add this offset
// note: the add is expressed as bitwise OR (|) since this saves us from writing
// brackets for operator precedence between + and <<
return uint64_t(id) | uint64_t(cpu) << 32u;
}
} // namespace ablastr::particles
#endif // ABLASTR_INDEX_HANDLING_H
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