1 /* bit search implementation 2 * 3 * Copied from lib/find_bit.c to tools/lib/find_bit.c 4 * 5 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved. 6 * Written by David Howells (dhowells@redhat.com) 7 * 8 * Copyright (C) 2008 IBM Corporation 9 * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au> 10 * (Inspired by David Howell's find_next_bit implementation) 11 * 12 * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease 13 * size and improve performance, 2015. 14 * 15 * This program is free software; you can redistribute it and/or 16 * modify it under the terms of the GNU General Public License 17 * as published by the Free Software Foundation; either version 18 * 2 of the License, or (at your option) any later version. 19 */ 20 21 #include <linux/bitops.h> 22 #include <linux/bitmap.h> 23 #include <linux/kernel.h> 24 25 #if !defined(find_next_bit) 26 27 /* 28 * This is a common helper function for find_next_bit and 29 * find_next_zero_bit. The difference is the "invert" argument, which 30 * is XORed with each fetched word before searching it for one bits. 31 */ 32 static unsigned long _find_next_bit(const unsigned long *addr, 33 unsigned long nbits, unsigned long start, unsigned long invert) 34 { 35 unsigned long tmp; 36 37 if (!nbits || start >= nbits) 38 return nbits; 39 40 tmp = addr[start / BITS_PER_LONG] ^ invert; 41 42 /* Handle 1st word. */ 43 tmp &= BITMAP_FIRST_WORD_MASK(start); 44 start = round_down(start, BITS_PER_LONG); 45 46 while (!tmp) { 47 start += BITS_PER_LONG; 48 if (start >= nbits) 49 return nbits; 50 51 tmp = addr[start / BITS_PER_LONG] ^ invert; 52 } 53 54 return min(start + __ffs(tmp), nbits); 55 } 56 #endif 57 58 #ifndef find_next_bit 59 /* 60 * Find the next set bit in a memory region. 61 */ 62 unsigned long find_next_bit(const unsigned long *addr, unsigned long size, 63 unsigned long offset) 64 { 65 return _find_next_bit(addr, size, offset, 0UL); 66 } 67 #endif 68 69 #ifndef find_first_bit 70 /* 71 * Find the first set bit in a memory region. 72 */ 73 unsigned long find_first_bit(const unsigned long *addr, unsigned long size) 74 { 75 unsigned long idx; 76 77 for (idx = 0; idx * BITS_PER_LONG < size; idx++) { 78 if (addr[idx]) 79 return min(idx * BITS_PER_LONG + __ffs(addr[idx]), size); 80 } 81 82 return size; 83 } 84 #endif 85