1 files changed, 189 insertions, 0 deletions

diff --git a/src/common/bit_set.h b/src/common/bit_set.h
new file mode 100644
index 000000000..85f91e786
--- /dev/null
+++ b/src/common/bit_set.h
@@ -0,0 +1,189 @@
+// This file is under the public domain.
+
+#pragma once
+
+#include <cstddef>
+#ifdef _WIN32
+#include <intrin.h>
+#endif
+#include <initializer_list>
+#include <type_traits>
+#include "common/common_types.h"
+
+// namespace avoids conflict with OS X Carbon; don't use BitSet<T> directly
+namespace Common {
+
+// Helper functions:
+
+#ifdef _WIN32
+template <typename T>
+static inline int CountSetBits(T v)
+{
+    // from https://graphics.stanford.edu/~seander/bithacks.html
+    // GCC has this built in, but MSVC's intrinsic will only emit the actual
+    // POPCNT instruction, which we're not depending on
+    v = v - ((v >> 1) & (T)~(T)0/3);
+    v = (v & (T)~(T)0/15*3) + ((v >> 2) & (T)~(T)0/15*3);
+    v = (v + (v >> 4)) & (T)~(T)0/255*15;
+    return (T)(v * ((T)~(T)0/255)) >> (sizeof(T) - 1) * 8;
+}
+static inline int LeastSignificantSetBit(u8 val)
+{
+    unsigned long index;
+    _BitScanForward(&index, val);
+    return (int)index;
+}
+static inline int LeastSignificantSetBit(u16 val)
+{
+    unsigned long index;
+    _BitScanForward(&index, val);
+    return (int)index;
+}
+static inline int LeastSignificantSetBit(u32 val)
+{
+    unsigned long index;
+    _BitScanForward(&index, val);
+    return (int)index;
+}
+static inline int LeastSignificantSetBit(u64 val)
+{
+    unsigned long index;
+    _BitScanForward64(&index, val);
+    return (int)index;
+}
+#else
+static inline int CountSetBits(u8 val) { return __builtin_popcount(val); }
+static inline int CountSetBits(u16 val) { return __builtin_popcount(val); }
+static inline int CountSetBits(u32 val) { return __builtin_popcount(val); }
+static inline int CountSetBits(u64 val) { return __builtin_popcountll(val); }
+static inline int LeastSignificantSetBit(u8 val) { return __builtin_ctz(val); }
+static inline int LeastSignificantSetBit(u16 val) { return __builtin_ctz(val); }
+static inline int LeastSignificantSetBit(u32 val) { return __builtin_ctz(val); }
+static inline int LeastSignificantSetBit(u64 val) { return __builtin_ctzll(val); }
+#endif
+
+// Similar to std::bitset, this is a class which encapsulates a bitset, i.e.
+// using the set bits of an integer to represent a set of integers.  Like that
+// class, it acts like an array of bools:
+//     BitSet32 bs;
+//     bs[1] = true;
+// but also like the underlying integer ([0] = least significant bit):
+//     BitSet32 bs2 = ...;
+//     bs = (bs ^ bs2) & BitSet32(0xffff);
+// The following additional functionality is provided:
+// - Construction using an initializer list.
+//     BitSet bs { 1, 2, 4, 8 };
+// - Efficiently iterating through the set bits:
+//     for (int i : bs)
+//         [i is the *index* of a set bit]
+//   (This uses the appropriate CPU instruction to find the next set bit in one
+//   operation.)
+// - Counting set bits using .Count() - see comment on that method.
+
+// TODO: use constexpr when MSVC gets out of the Dark Ages
+
+template <typename IntTy>
+class BitSet
+{
+    static_assert(!std::is_signed<IntTy>::value, "BitSet should not be used with signed types");
+public:
+    // A reference to a particular bit, returned from operator[].
+    class Ref
+    {
+    public:
+        Ref(Ref&& other) : m_bs(other.m_bs), m_mask(other.m_mask) {}
+        Ref(BitSet* bs, IntTy mask) : m_bs(bs), m_mask(mask) {}
+        operator bool() const { return (m_bs->m_val & m_mask) != 0; }
+        bool operator=(bool set)
+        {
+            m_bs->m_val = (m_bs->m_val & ~m_mask) | (set ? m_mask : 0);
+            return set;
+        }
+    private:
+        BitSet* m_bs;
+        IntTy m_mask;
+    };
+
+    // A STL-like iterator is required to be able to use range-based for loops.
+    class Iterator
+    {
+    public:
+        Iterator(const Iterator& other) : m_val(other.m_val), m_bit(other.m_bit) {}
+        Iterator(IntTy val, int bit) : m_val(val), m_bit(bit) {}
+        Iterator& operator=(Iterator other) { new (this) Iterator(other); return *this; }
+        int operator*() { return m_bit; }
+        Iterator& operator++()
+        {
+            if (m_val == 0)
+            {
+                m_bit = -1;
+            }
+            else
+            {
+                int bit = LeastSignificantSetBit(m_val);
+                m_val &= ~(1 << bit);
+                m_bit = bit;
+            }
+            return *this;
+        }
+        Iterator operator++(int _)
+        {
+            Iterator other(*this);
+            ++*this;
+            return other;
+        }
+        bool operator==(Iterator other) const { return m_bit == other.m_bit; }
+        bool operator!=(Iterator other) const { return m_bit != other.m_bit; }
+    private:
+        IntTy m_val;
+        int m_bit;
+    };
+
+    BitSet() : m_val(0) {}
+    explicit BitSet(IntTy val) : m_val(val) {}
+    BitSet(std::initializer_list<int> init)
+    {
+        m_val = 0;
+        for (int bit : init)
+            m_val |= (IntTy)1 << bit;
+    }
+
+    static BitSet AllTrue(size_t count)
+    {
+        return BitSet(count == sizeof(IntTy)*8 ? ~(IntTy)0 : (((IntTy)1 << count) - 1));
+    }
+
+    Ref operator[](size_t bit) { return Ref(this, (IntTy)1 << bit); }
+    const Ref operator[](size_t bit) const { return (*const_cast<BitSet*>(this))[bit]; }
+    bool operator==(BitSet other) const { return m_val == other.m_val; }
+    bool operator!=(BitSet other) const { return m_val != other.m_val; }
+    bool operator<(BitSet other) const { return m_val < other.m_val; }
+    bool operator>(BitSet other) const { return m_val > other.m_val; }
+    BitSet operator|(BitSet other) const { return BitSet(m_val | other.m_val); }
+    BitSet operator&(BitSet other) const { return BitSet(m_val & other.m_val); }
+    BitSet operator^(BitSet other) const { return BitSet(m_val ^ other.m_val); }
+    BitSet operator~() const { return BitSet(~m_val); }
+    BitSet& operator|=(BitSet other) { return *this = *this | other; }
+    BitSet& operator&=(BitSet other) { return *this = *this & other; }
+    BitSet& operator^=(BitSet other) { return *this = *this ^ other; }
+    operator u32() = delete;
+    operator bool() { return m_val != 0; }
+
+    // Warning: Even though on modern CPUs this is a single fast instruction,
+    // Dolphin's official builds do not currently assume POPCNT support on x86,
+    // so slower explicit bit twiddling is generated.  Still should generally
+    // be faster than a loop.
+    unsigned int Count() const { return CountSetBits(m_val); }
+
+    Iterator begin() const { Iterator it(m_val, 0); return ++it; }
+    Iterator end() const { return Iterator(m_val, -1); }
+
+    IntTy m_val;
+};
+
+} // Common
+
+typedef Common::BitSet<u8> BitSet8;
+typedef Common::BitSet<u16> BitSet16;
+typedef Common::BitSet<u32> BitSet32;
+typedef Common::BitSet<u64> BitSet64;
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