log2.h 4.4 KB

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  1. /* Integer base 2 logarithm calculation
  2. *
  3. * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
  4. * Written by David Howells (dhowells@redhat.com)
  5. *
  6. * This program is free software; you can redistribute it and/or
  7. * modify it under the terms of the GNU General Public License
  8. * as published by the Free Software Foundation; either version
  9. * 2 of the License, or (at your option) any later version.
  10. */
  11. #ifndef _LINUX_LOG2_H
  12. #define _LINUX_LOG2_H
  13. #include <linux/types.h>
  14. #include <linux/bitops.h>
  15. /*
  16. * deal with unrepresentable constant logarithms
  17. */
  18. extern __attribute__((const, noreturn))
  19. int ____ilog2_NaN(void);
  20. /*
  21. * non-constant log of base 2 calculators
  22. * - the arch may override these in asm/bitops.h if they can be implemented
  23. * more efficiently than using fls() and fls64()
  24. * - the arch is not required to handle n==0 if implementing the fallback
  25. */
  26. #ifndef CONFIG_ARCH_HAS_ILOG2_U32
  27. static inline __attribute__((const))
  28. int __ilog2_u32(u32 n)
  29. {
  30. return fls(n) - 1;
  31. }
  32. #endif
  33. #ifndef CONFIG_ARCH_HAS_ILOG2_U64
  34. static inline __attribute__((const))
  35. int __ilog2_u64(u64 n)
  36. {
  37. return fls64(n) - 1;
  38. }
  39. #endif
  40. /*
  41. * Determine whether some value is a power of two, where zero is
  42. * *not* considered a power of two.
  43. */
  44. static inline __attribute__((const))
  45. bool is_power_of_2(unsigned long n)
  46. {
  47. return (n != 0 && ((n & (n - 1)) == 0));
  48. }
  49. /*
  50. * round up to nearest power of two
  51. */
  52. static inline __attribute__((const))
  53. unsigned long __roundup_pow_of_two(unsigned long n)
  54. {
  55. return 1UL << fls_long(n - 1);
  56. }
  57. /**
  58. * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
  59. * @n - parameter
  60. *
  61. * constant-capable log of base 2 calculation
  62. * - this can be used to initialise global variables from constant data, hence
  63. * the massive ternary operator construction
  64. *
  65. * selects the appropriately-sized optimised version depending on sizeof(n)
  66. */
  67. #define ilog2(n) \
  68. ( \
  69. __builtin_constant_p(n) ? ( \
  70. (n) < 1 ? ____ilog2_NaN() : \
  71. (n) & (1ULL << 63) ? 63 : \
  72. (n) & (1ULL << 62) ? 62 : \
  73. (n) & (1ULL << 61) ? 61 : \
  74. (n) & (1ULL << 60) ? 60 : \
  75. (n) & (1ULL << 59) ? 59 : \
  76. (n) & (1ULL << 58) ? 58 : \
  77. (n) & (1ULL << 57) ? 57 : \
  78. (n) & (1ULL << 56) ? 56 : \
  79. (n) & (1ULL << 55) ? 55 : \
  80. (n) & (1ULL << 54) ? 54 : \
  81. (n) & (1ULL << 53) ? 53 : \
  82. (n) & (1ULL << 52) ? 52 : \
  83. (n) & (1ULL << 51) ? 51 : \
  84. (n) & (1ULL << 50) ? 50 : \
  85. (n) & (1ULL << 49) ? 49 : \
  86. (n) & (1ULL << 48) ? 48 : \
  87. (n) & (1ULL << 47) ? 47 : \
  88. (n) & (1ULL << 46) ? 46 : \
  89. (n) & (1ULL << 45) ? 45 : \
  90. (n) & (1ULL << 44) ? 44 : \
  91. (n) & (1ULL << 43) ? 43 : \
  92. (n) & (1ULL << 42) ? 42 : \
  93. (n) & (1ULL << 41) ? 41 : \
  94. (n) & (1ULL << 40) ? 40 : \
  95. (n) & (1ULL << 39) ? 39 : \
  96. (n) & (1ULL << 38) ? 38 : \
  97. (n) & (1ULL << 37) ? 37 : \
  98. (n) & (1ULL << 36) ? 36 : \
  99. (n) & (1ULL << 35) ? 35 : \
  100. (n) & (1ULL << 34) ? 34 : \
  101. (n) & (1ULL << 33) ? 33 : \
  102. (n) & (1ULL << 32) ? 32 : \
  103. (n) & (1ULL << 31) ? 31 : \
  104. (n) & (1ULL << 30) ? 30 : \
  105. (n) & (1ULL << 29) ? 29 : \
  106. (n) & (1ULL << 28) ? 28 : \
  107. (n) & (1ULL << 27) ? 27 : \
  108. (n) & (1ULL << 26) ? 26 : \
  109. (n) & (1ULL << 25) ? 25 : \
  110. (n) & (1ULL << 24) ? 24 : \
  111. (n) & (1ULL << 23) ? 23 : \
  112. (n) & (1ULL << 22) ? 22 : \
  113. (n) & (1ULL << 21) ? 21 : \
  114. (n) & (1ULL << 20) ? 20 : \
  115. (n) & (1ULL << 19) ? 19 : \
  116. (n) & (1ULL << 18) ? 18 : \
  117. (n) & (1ULL << 17) ? 17 : \
  118. (n) & (1ULL << 16) ? 16 : \
  119. (n) & (1ULL << 15) ? 15 : \
  120. (n) & (1ULL << 14) ? 14 : \
  121. (n) & (1ULL << 13) ? 13 : \
  122. (n) & (1ULL << 12) ? 12 : \
  123. (n) & (1ULL << 11) ? 11 : \
  124. (n) & (1ULL << 10) ? 10 : \
  125. (n) & (1ULL << 9) ? 9 : \
  126. (n) & (1ULL << 8) ? 8 : \
  127. (n) & (1ULL << 7) ? 7 : \
  128. (n) & (1ULL << 6) ? 6 : \
  129. (n) & (1ULL << 5) ? 5 : \
  130. (n) & (1ULL << 4) ? 4 : \
  131. (n) & (1ULL << 3) ? 3 : \
  132. (n) & (1ULL << 2) ? 2 : \
  133. (n) & (1ULL << 1) ? 1 : \
  134. (n) & (1ULL << 0) ? 0 : \
  135. ____ilog2_NaN() \
  136. ) : \
  137. (sizeof(n) <= 4) ? \
  138. __ilog2_u32(n) : \
  139. __ilog2_u64(n) \
  140. )
  141. /**
  142. * roundup_pow_of_two - round the given value up to nearest power of two
  143. * @n - parameter
  144. *
  145. * round the given value up to the nearest power of two
  146. * - the result is undefined when n == 0
  147. * - this can be used to initialise global variables from constant data
  148. */
  149. #define roundup_pow_of_two(n) \
  150. ( \
  151. __builtin_constant_p(n) ? ( \
  152. (n == 1) ? 0 : \
  153. (1UL << (ilog2((n) - 1) + 1)) \
  154. ) : \
  155. __roundup_pow_of_two(n) \
  156. )
  157. #endif /* _LINUX_LOG2_H */