1 /* SPDX-License-Identifier: GPL-2.0-or-later */ 2 /* Count leading and trailing zeros functions 3 * 4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells@redhat.com) 6 */ 7 8 #ifndef _LINUX_BITOPS_COUNT_ZEROS_H_ 9 #define _LINUX_BITOPS_COUNT_ZEROS_H_ 10 11 #include <asm/bitops.h> 12 13 /** 14 * count_leading_zeros - Count the number of zeros from the MSB back 15 * @x: The value 16 * 17 * Count the number of leading zeros from the MSB going towards the LSB in @x. 18 * 19 * If the MSB of @x is set, the result is 0. 20 * If only the LSB of @x is set, then the result is BITS_PER_LONG-1. 21 * If @x is 0 then the result is COUNT_LEADING_ZEROS_0. 22 */ 23 static inline int count_leading_zeros(unsigned long x) 24 { 25 if (sizeof(x) == 4) 26 return BITS_PER_LONG - fls(x); 27 else 28 return BITS_PER_LONG - fls64(x); 29 } 30 31 #define COUNT_LEADING_ZEROS_0 BITS_PER_LONG 32 33 /** 34 * count_trailing_zeros - Count the number of zeros from the LSB forwards 35 * @x: The value 36 * 37 * Count the number of trailing zeros from the LSB going towards the MSB in @x. 38 * 39 * If the LSB of @x is set, the result is 0. 40 * If only the MSB of @x is set, then the result is BITS_PER_LONG-1. 41 * If @x is 0 then the result is COUNT_TRAILING_ZEROS_0. 42 */ 43 static inline int count_trailing_zeros(unsigned long x) 44 { 45 #define COUNT_TRAILING_ZEROS_0 (-1) 46 47 if (sizeof(x) == 4) 48 return ffs(x); 49 else 50 return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0; 51 } 52 53 #endif /* _LINUX_BITOPS_COUNT_ZEROS_H_ */ 54