aacf29bf1b
Provide count_leading/trailing_zeros() macros based on extant arch bit scanning functions rather than reimplementing from scratch in MPILIB. Whilst we're at it, turn count_foo_zeros(n, x) into n = count_foo_zeros(x). Also move the definition to asm-generic as other people may be interested in using it. Signed-off-by: David Howells <dhowells@redhat.com> Cc: David S. Miller <davem@davemloft.net> Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.com> Cc: Arnd Bergmann <arnd@arndb.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
57 lines
1.6 KiB
C
57 lines
1.6 KiB
C
/* Count leading and trailing zeros functions
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*
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* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#ifndef _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_
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#define _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_
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#include <asm/bitops.h>
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/**
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* count_leading_zeros - Count the number of zeros from the MSB back
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* @x: The value
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*
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* Count the number of leading zeros from the MSB going towards the LSB in @x.
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*
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* If the MSB of @x is set, the result is 0.
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* If only the LSB of @x is set, then the result is BITS_PER_LONG-1.
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* If @x is 0 then the result is COUNT_LEADING_ZEROS_0.
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*/
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static inline int count_leading_zeros(unsigned long x)
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{
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if (sizeof(x) == 4)
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return BITS_PER_LONG - fls(x);
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else
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return BITS_PER_LONG - fls64(x);
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}
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#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG
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/**
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* count_trailing_zeros - Count the number of zeros from the LSB forwards
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* @x: The value
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*
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* Count the number of trailing zeros from the LSB going towards the MSB in @x.
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*
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* If the LSB of @x is set, the result is 0.
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* If only the MSB of @x is set, then the result is BITS_PER_LONG-1.
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* If @x is 0 then the result is COUNT_TRAILING_ZEROS_0.
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*/
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static inline int count_trailing_zeros(unsigned long x)
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{
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#define COUNT_TRAILING_ZEROS_0 (-1)
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if (sizeof(x) == 4)
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return ffs(x);
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else
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return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0;
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}
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#endif /* _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_ */
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