libc/src/__support/CPP/bitset.h

   1 //===-- A self contained equivalent of std::bitset --------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC___SUPPORT_CPP_BITSET_H
  10 #define LLVM_LIBC_SRC___SUPPORT_CPP_BITSET_H
  11
  12 #include "src/__support/macros/attributes.h"
  13 #include <stddef.h> // For size_t.
  14
  15 namespace LIBC_NAMESPACE::cpp {
  16
  17 template <size_t NumberOfBits> struct bitset {
  18   static_assert(NumberOfBits != 0,
  19                 "Cannot create a LIBC_NAMESPACE::cpp::bitset of size 0.");
  20
  21   LIBC_INLINE constexpr void set(size_t Index) {
  22     Data[Index / BITS_PER_UNIT] |= mask(Index);
  23   }
  24
  25   LIBC_INLINE constexpr void reset() {
  26     for (size_t i = 0; i < NUMBER_OF_UNITS; ++i)
  27       Data[i] = 0;
  28   }
  29
  30   LIBC_INLINE constexpr bool test(size_t Index) const {
  31     return Data[Index / BITS_PER_UNIT] & mask(Index);
  32   }
  33
  34   LIBC_INLINE constexpr void flip() {
  35     for (size_t i = 0; i < NUMBER_OF_UNITS; ++i)
  36       Data[i] = ~Data[i];
  37   }
  38
  39   // This function sets all bits in the range from Start to End (inclusive) to
  40   // true. It assumes that Start <= End.
  41   LIBC_INLINE constexpr void set_range(size_t Start, size_t End) {
  42     size_t start_index = Start / BITS_PER_UNIT;
  43     size_t end_index = End / BITS_PER_UNIT;
  44
  45     if (start_index == end_index) {
  46       // The reason the left shift is split into two parts (instead of just left
  47       // shifting by End - Start + 1) is because when a number is shifted left
  48       // by 64 then it wraps around to doing nothing, but shifting by 63 and the
  49       // shifting by 1 correctly shifts away all of the bits.
  50       size_t bit_mask = (((size_t(1) << (End - Start)) << 1) - 1)
  51                         << (Start - (start_index * BITS_PER_UNIT));
  52       Data[start_index] |= bit_mask;
  53     } else {
  54       size_t low_bit_mask =
  55           ~((size_t(1) << (Start - (start_index * BITS_PER_UNIT))) - 1);
  56       Data[start_index] |= low_bit_mask;
  57
  58       for (size_t i = start_index + 1; i < end_index; ++i)
  59         Data[i] = ~size_t(0);
  60
  61       // Same as above, by splitting the shift the behavior is more consistent.
  62       size_t high_bit_mask =
  63           ((size_t(1) << (End - (end_index * BITS_PER_UNIT))) << 1) - 1;
  64       Data[end_index] |= high_bit_mask;
  65     }
  66   }
  67
  68   LIBC_INLINE constexpr bool operator==(const bitset<NumberOfBits> &other) {
  69     for (size_t i = 0; i < NUMBER_OF_UNITS; ++i) {
  70       if (Data[i] != other.Data[i])
  71         return false;
  72     }
  73     return true;
  74   }
  75
  76 private:
  77   static constexpr size_t BITS_PER_BYTE = 8;
  78   static constexpr size_t BITS_PER_UNIT = BITS_PER_BYTE * sizeof(size_t);
  79   static constexpr size_t NUMBER_OF_UNITS =
  80       (NumberOfBits + BITS_PER_UNIT - 1) / BITS_PER_UNIT;
  81
  82   LIBC_INLINE static constexpr size_t mask(size_t Index) {
  83     return size_t{1} << (Index % BITS_PER_UNIT);
  84   }
  85   size_t Data[NUMBER_OF_UNITS] = {0};
  86 };
  87
  88 } // namespace LIBC_NAMESPACE::cpp
  89
  90 #endif // LLVM_LIBC_SRC___SUPPORT_CPP_BITSET_H