src/base/intmath.hh

   1 /*
   2  * Copyright (c) 2001, 2003-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef __BASE_INTMATH_HH__
  30 #define __BASE_INTMATH_HH__
  31
  32 #include <cassert>
  33 #include <cstdint>
  34 #include <type_traits>
  35
  36 #include "base/logging.hh"
  37 #include "base/types.hh"
  38
  39 /**
  40  * @ingroup api_base_utils
  41  */
  42 inline uint64_t
  43 power(uint32_t n, uint32_t e)
  44 {
  45     uint64_t result = 1;
  46     uint64_t component = n;
  47     while (e) {
  48         uint64_t last = result;
  49         if (e & 0x1)
  50             result *= component;
  51         warn_if(result < last, "power() overflowed!");
  52         e >>= 1;
  53         component *= component;
  54     }
  55     return result;
  56 }
  57
  58 /**
  59  * @ingroup api_base_utils
  60  */
  61 template <class T>
  62 inline typename std::enable_if_t<std::is_integral<T>::value, int>
  63 floorLog2(T x)
  64 {
  65     assert(x > 0);
  66
  67     // A guaranteed unsigned version of x.
  68     uint64_t ux = (typename std::make_unsigned<T>::type)x;
  69
  70     int y = 0;
  71     constexpr auto ts = sizeof(T);
  72
  73     if (ts >= 8 && (ux & ULL(0xffffffff00000000))) { y += 32; ux >>= 32; }
  74     if (ts >= 4 && (ux & ULL(0x00000000ffff0000))) { y += 16; ux >>= 16; }
  75     if (ts >= 2 && (ux & ULL(0x000000000000ff00))) { y +=  8; ux >>=  8; }
  76     if (ux & ULL(0x00000000000000f0)) { y +=  4; ux >>=  4; }
  77     if (ux & ULL(0x000000000000000c)) { y +=  2; ux >>=  2; }
  78     if (ux & ULL(0x0000000000000002)) { y +=  1; }
  79
  80     return y;
  81 }
  82
  83 /**
  84  * @ingroup api_base_utils
  85  */
  86 template <class T>
  87 inline int
  88 ceilLog2(const T& n)
  89 {
  90     assert(n > 0);
  91     if (n == 1)
  92         return 0;
  93
  94     return floorLog2(n - (T)1) + 1;
  95 }
  96
  97 /**
  98  * @ingroup api_base_utils
  99  */
 100 template <class T>
 101 inline bool
 102 isPowerOf2(const T& n)
 103 {
 104     // If n is non-zero, and subtracting one borrows all the way to the MSB
 105     // and flips all bits, then this is a power of 2.
 106     return n && !(n & (n - 1));
 107 }
 108
 109 /**
 110  * @ingroup api_base_utils
 111  */
 112 template <class T, class U>
 113 inline T
 114 divCeil(const T& a, const U& b)
 115 {
 116     return (a + b - 1) / b;
 117 }
 118
 119 /**
 120  * This function is used to align addresses in memory.
 121  *
 122  * @param val is the address to be aligned.
 123  * @param align is the alignment. Can only be a power of 2.
 124  * @return The aligned address. The smallest number divisible
 125  * by @param align which is greater than or equal to @param val.
 126  *
 127  * @ingroup api_base_utils
 128  */
 129 template <class T, class U>
 130 inline T
 131 roundUp(const T& val, const U& align)
 132 {
 133     assert(isPowerOf2(align));
 134     T mask = (T)align - 1;
 135     return (val + mask) & ~mask;
 136 }
 137
 138 /**
 139  * This function is used to align addresses in memory.
 140  *
 141  * @param val is the address to be aligned.
 142  * @param align is the alignment. Can only be a power of 2.
 143  * @return The aligned address. The biggest number divisible
 144  * by @param align which is less than or equal to @param val.
 145  *
 146  * @ingroup api_base_utils
 147  */
 148 template <class T, class U>
 149 inline T
 150 roundDown(const T& val, const U& align)
 151 {
 152     assert(isPowerOf2(align));
 153     T mask = (T)align - 1;
 154     return val & ~mask;
 155 }
 156
 157 #endif // __BASE_INTMATH_HH__