mirror of
https://github.com/matrix-construct/construct
synced 2024-09-18 14:38:55 +02:00
65 lines
1.7 KiB
C++
65 lines
1.7 KiB
C++
// The Construct
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//
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// Copyright (C) The Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2020 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_SIMD_TZCNT_H
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namespace ircd::simd
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{
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template<class T> uint tzcnt(const T) noexcept;
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}
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/// Convenience template. Unfortunately this drops to scalar until specific
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/// targets and specializations are created.
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template<class T>
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inline uint
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__attribute__((target("lzcnt")))
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ircd::simd::tzcnt(const T a)
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noexcept
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{
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// The behavior of lzcnt/tzcnt can differ among platforms; when false we
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// lzcnt/tzcnt to fall back to bsr/bsf-like behavior.
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constexpr auto bitscan
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{
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#ifdef __LZCNT__
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false
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#else
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true
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#endif
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};
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uint ret(0), i(lanes<T>()), mask(-1U); do
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{
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if constexpr(bitscan && sizeof_lane<T>() <= sizeof(u16))
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ret += (15 - __lzcnt16(a[--i])) & mask;
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else if constexpr(sizeof_lane<T>() <= sizeof(u16))
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ret += __lzcnt16(a[--i]) & mask;
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else if constexpr(bitscan && sizeof_lane<T>() <= sizeof(u32))
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ret += (31 - __lzcnt32(a[--i])) & mask;
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else if constexpr(sizeof_lane<T>() <= sizeof(u32))
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ret += __lzcnt32(a[--i]) & mask;
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else if constexpr(bitscan)
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ret += (63 - __lzcnt64(a[--i])) & mask;
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else
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ret += __lzcnt64(a[--i]) & mask;
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static const auto lane_bits(sizeof_lane<T>() * 8);
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mask &= boolmask(uint(ret % lane_bits == 0));
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mask &= boolmask(uint(ret != 0));
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}
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while(i);
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return ret;
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}
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