lib/ccan/ilog/ilog.h

   1 #if !defined(_ilog_H)
   2 # define _ilog_H (1)
   3 # include "config.h"
   4 # include <stdint.h>
   5 # include <limits.h>
   6 # include <ccan/compiler/compiler.h>
   7
   8 /**
   9  * ilog32 - Integer binary logarithm of a 32-bit value.
  10  * @_v: A 32-bit value.
  11  * Returns floor(log2(_v))+1, or 0 if _v==0.
  12  * This is the number of bits that would be required to represent _v in two's
  13  *  complement notation with all of the leading zeros stripped.
  14  * Note that many uses will resolve to the fast macro version instead.
  15  *
  16  * See Also:
  17  *      ilog32_nz(), ilog64()
  18  *
  19  * Example:
  20  *      // Rounds up to next power of 2 (if not a power of 2).
  21  *      static uint32_t round_up32(uint32_t i)
  22  *      {
  23  *              assert(i != 0);
  24  *              return 1U << ilog32(i-1);
  25  *      }
  26  */
  27 int ilog32(uint32_t _v) IDEMPOTENT;
  28
  29 /**
  30  * ilog32_nz - Integer binary logarithm of a non-zero 32-bit value.
  31  * @_v: A 32-bit value.
  32  * Returns floor(log2(_v))+1, or undefined if _v==0.
  33  * This is the number of bits that would be required to represent _v in two's
  34  *  complement notation with all of the leading zeros stripped.
  35  * Note that many uses will resolve to the fast macro version instead.
  36  * See Also:
  37  *      ilog32(), ilog64_nz()
  38  * Example:
  39  *      // Find Last Set (ie. highest bit set, 0 to 31).
  40  *      static uint32_t fls32(uint32_t i)
  41  *      {
  42  *              assert(i != 0);
  43  *              return ilog32_nz(i) - 1;
  44  *      }
  45  */
  46 int ilog32_nz(uint32_t _v) IDEMPOTENT;
  47
  48 /**
  49  * ilog64 - Integer binary logarithm of a 64-bit value.
  50  * @_v: A 64-bit value.
  51  * Returns floor(log2(_v))+1, or 0 if _v==0.
  52  * This is the number of bits that would be required to represent _v in two's
  53  *  complement notation with all of the leading zeros stripped.
  54  * Note that many uses will resolve to the fast macro version instead.
  55  * See Also:
  56  *      ilog64_nz(), ilog32()
  57  */
  58 int ilog64(uint64_t _v) IDEMPOTENT;
  59
  60 /**
  61  * ilog64_nz - Integer binary logarithm of a non-zero 64-bit value.
  62  * @_v: A 64-bit value.
  63  * Returns floor(log2(_v))+1, or undefined if _v==0.
  64  * This is the number of bits that would be required to represent _v in two's
  65  *  complement notation with all of the leading zeros stripped.
  66  * Note that many uses will resolve to the fast macro version instead.
  67  * See Also:
  68  *      ilog64(), ilog32_nz()
  69  */
  70 int ilog64_nz(uint64_t _v) IDEMPOTENT;
  71
  72 /**
  73  * STATIC_ILOG_32 - The integer logarithm of an (unsigned, 32-bit) constant.
  74  * @_v: A non-negative 32-bit constant.
  75  * Returns floor(log2(_v))+1, or 0 if _v==0.
  76  * This is the number of bits that would be required to represent _v in two's
  77  *  complement notation with all of the leading zeros stripped.
  78  * This macro should only be used when you need a compile-time constant,
  79  * otherwise ilog32 or ilog32_nz are just as fast and more flexible.
  80  *
  81  * Example:
  82  *      #define MY_PAGE_SIZE    4096
  83  *      #define MY_PAGE_BITS    (STATIC_ILOG_32(PAGE_SIZE) - 1)
  84  */
  85 #define STATIC_ILOG_32(_v) (STATIC_ILOG5((uint32_t)(_v)))
  86
  87 /**
  88  * STATIC_ILOG_64 - The integer logarithm of an (unsigned, 64-bit) constant.
  89  * @_v: A non-negative 64-bit constant.
  90  * Returns floor(log2(_v))+1, or 0 if _v==0.
  91  * This is the number of bits that would be required to represent _v in two's
  92  *  complement notation with all of the leading zeros stripped.
  93  * This macro should only be used when you need a compile-time constant,
  94  * otherwise ilog64 or ilog64_nz are just as fast and more flexible.
  95  */
  96 #define STATIC_ILOG_64(_v) (STATIC_ILOG6((uint64_t)(_v)))
  97
  98 /* Private implementation details */
  99
 100 /*Note the casts to (int) below: this prevents "upgrading"
 101    the type of an entire expression to an (unsigned) size_t.*/
 102 #if INT_MAX>=2147483647 && HAVE_BUILTIN_CLZ
 103 #define builtin_ilog32_nz(v) \
 104         (((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clz(v))
 105 #elif LONG_MAX>=2147483647L && HAVE_BUILTIN_CLZL
 106 #define builtin_ilog32_nz(v) \
 107         (((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clzl(v))
 108 #endif
 109
 110 #if INT_MAX>=9223372036854775807LL && HAVE_BUILTIN_CLZ
 111 #define builtin_ilog64_nz(v) \
 112         (((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clz(v))
 113 #elif LONG_MAX>=9223372036854775807LL && HAVE_BUILTIN_CLZL
 114 #define builtin_ilog64_nz(v) \
 115         (((int)sizeof(unsigned long)*CHAR_BIT) - __builtin_clzl(v))
 116 #elif HAVE_BUILTIN_CLZLL
 117 #define builtin_ilog64_nz(v) \
 118         (((int)sizeof(unsigned long long)*CHAR_BIT) - __builtin_clzll(v))
 119 #endif
 120
 121 #ifdef builtin_ilog32_nz
 122 #define ilog32(_v) (builtin_ilog32_nz(_v)&-!!(_v))
 123 #define ilog32_nz(_v) builtin_ilog32_nz(_v)
 124 #else
 125 #define ilog32_nz(_v) ilog32(_v)
 126 #define ilog32(_v) (IS_COMPILE_CONSTANT(_v) ? STATIC_ILOG_32(_v) : ilog32(_v))
 127 #endif /* builtin_ilog32_nz */
 128
 129 #ifdef builtin_ilog64_nz
 130 #define ilog64(_v) (builtin_ilog64_nz(_v)&-!!(_v))
 131 #define ilog64_nz(_v) builtin_ilog64_nz(_v)
 132 #else
 133 #define ilog64_nz(_v) ilog64(_v)
 134 #define ilog64(_v) (IS_COMPILE_CONSTANT(_v) ? STATIC_ILOG_64(_v) : ilog64(_v))
 135 #endif /* builtin_ilog64_nz */
 136
 137 /* Macros for evaluating compile-time constant ilog. */
 138 # define STATIC_ILOG0(_v) (!!(_v))
 139 # define STATIC_ILOG1(_v) (((_v)&0x2)?2:STATIC_ILOG0(_v))
 140 # define STATIC_ILOG2(_v) (((_v)&0xC)?2+STATIC_ILOG1((_v)>>2):STATIC_ILOG1(_v))
 141 # define STATIC_ILOG3(_v) \
 142  (((_v)&0xF0)?4+STATIC_ILOG2((_v)>>4):STATIC_ILOG2(_v))
 143 # define STATIC_ILOG4(_v) \
 144  (((_v)&0xFF00)?8+STATIC_ILOG3((_v)>>8):STATIC_ILOG3(_v))
 145 # define STATIC_ILOG5(_v) \
 146  (((_v)&0xFFFF0000)?16+STATIC_ILOG4((_v)>>16):STATIC_ILOG4(_v))
 147 # define STATIC_ILOG6(_v) \
 148  (((_v)&0xFFFFFFFF00000000ULL)?32+STATIC_ILOG5((_v)>>32):STATIC_ILOG5(_v))
 149
 150 #endif /* _ilog_H */