46 lines
1.2 KiB
C
46 lines
1.2 KiB
C
/* generic-clz.h - generic clz implementations.
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*
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* Copyright (C) 2024 Bruno Raoult ("br")
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* Licensed under the GNU General Public License v3.0 or later.
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* Some rights reserved. See COPYING.
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*
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* You should have received a copy of the GNU General Public License along with this
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* program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
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*
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* SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
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*
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*/
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#ifndef _GENERIC_CLZ_H_
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#define _GENERIC_CLZ_H_
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#include "br.h"
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/* Adapted from: http://www-graphics.stanford.edu/%7Eseander/bithacks.html
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*/
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static __always_inline int __clz32_emulated(u32 n)
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{
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uint r, q;
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r = (n > 0xFFFF) << 4; n >>= r;
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q = (n > 0xFF ) << 3; n >>= q; r |= q;
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q = (n > 0xF ) << 2; n >>= q; r |= q;
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q = (n > 0x3 ) << 1; n >>= q; r |= q;
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r |= (n >> 1);
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return 31 - r;
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}
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static __always_inline int __clz64_emulated(u64 n)
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{
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uint r, q;
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r = (n > 0xFFFFFFFF) << 5; n >>= r;
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q = (n > 0xFFFF) << 4; n >>= q; r |= q;
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q = (n > 0xFF ) << 3; n >>= q; r |= q;
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q = (n > 0xF ) << 2; n >>= q; r |= q;
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q = (n > 0x3 ) << 1; n >>= q; r |= q;
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r |= (n >> 1);
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return 63 - r;
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}
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#endif /* _GENERIC_CLZ_H_ */
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