1 //------------------------------------------------------------------------------ 2 // GB_log2.h: integer log2 and check if power of 2 3 //------------------------------------------------------------------------------ 4 5 // SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2021, All Rights Reserved. 6 // SPDX-License-Identifier: Apache-2.0 7 8 //------------------------------------------------------------------------------ 9 10 #ifndef GB_LOG2_H 11 #define GB_LOG2_H 12 13 // # of bits in an unsigned long long, normally 64 14 #define GB_64 (8 * sizeof (unsigned long long)) 15 16 // floor and ceiling of the log2 of an integer. 17 #ifdef __GNUC__ 18 // see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html 19 #define GB_CLZLL(k) __builtin_clzll ((unsigned long long) (k)) 20 #define GB_CEIL_LOG2(k) ((uint64_t) ((k) < 2) ? 0 : (GB_64 - GB_CLZLL ((k)-1))) 21 #define GB_FLOOR_LOG2(k) ((uint64_t) ((k) < 2) ? 0 : (GB_64 - GB_CLZLL (k) - 1)) 22 #else 23 #define GB_CLZLL(k) not defined, using log2 instead 24 #define GB_CEIL_LOG2(k) ((uint64_t) (ceil (log2 ((double) k)))) 25 #define GB_FLOOR_LOG2(k) ((uint64_t) (floor (log2 ((double) k)))) 26 #endif 27 28 // GB_IS_POWER_OF_TWO(k) is true if the unsigned integer k is an exact power of 29 // two, or if k is zero. This expression should not be used if k is negative. 30 #define GB_IS_POWER_OF_TWO(k) (((k) & ((k) - 1)) == 0) 31 32 #endif 33 34