From 96fc17b99d56eb636c894c5be9ab39bfdb4ba454 Mon Sep 17 00:00:00 2001
From: Chris Xiong <chirs241097@gmail.com>
Date: Sat, 27 Aug 2022 00:55:38 -0400
Subject: Initial code dump.

---
 compressed_vector.hpp | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 compressed_vector.hpp

(limited to 'compressed_vector.hpp')

diff --git a/compressed_vector.hpp b/compressed_vector.hpp
new file mode 100644
index 0000000..db820ed
--- /dev/null
+++ b/compressed_vector.hpp
@@ -0,0 +1,90 @@
+#ifndef COMPRESSED_VECTOR
+#define COMPRESSED_VECTOR
+
+#include <cstdint>
+#include <cstddef>
+#include <vector>
+
+template <class T, int B>
+struct compressed_vector_hash;
+
+/*limitations:
+ *  current implementation never returns a reference
+ */
+template <class T, int B>
+class compressed_vector
+{
+    static_assert(std::is_unsigned<T>::value);
+    static_assert(sizeof(T) * 8 >= B);
+    static_assert(B > 0 && B < 64);
+private:
+    const int P = 64 / B;
+    const uint64_t M = (1 << B) - 1;
+    std::vector<uint64_t> v;
+    size_t sz;
+public:
+    compressed_vector() : sz(0) {}
+    void push_back(T val)
+    {
+        //assert(v <= M);
+        if (sz % P == 0)
+            v.push_back(0);
+        set(sz, val);
+        ++sz;
+    }
+    void pop_back()
+    {
+        //assert(sz > 0);
+        if (--sz % P == 0)
+            v.pop_back();
+        else
+        //zero out the now unused bits
+            v[sz / P] &= ~(M << (sz % P * B));
+    }
+    T front() const {return get(0);}
+    T back() const {return get(sz - 1);}
+    T get(size_t i) const
+    {
+        //assert(i < sz);
+        return (T)((v[i / P] >> (i % P * B)) & M);
+    }
+    void set(size_t i, T val)
+    {
+        //assert(i < sz);
+        v[i / P] &= ~(M << (i % P * B));
+        v[i / P] |= ((uint64_t) val) << (i % P * B);
+    }
+    size_t size() const
+    {
+        return sz;
+    }
+    void clear()
+    {
+        sz = 0;
+        v.clear();
+    }
+
+    bool operator ==(const compressed_vector& other) const
+    {
+        return sz == other.sz && v == other.v;
+    }
+
+    friend struct compressed_vector_hash<T, B>;
+};
+
+template <class T, int B>
+struct compressed_vector_hash
+{
+    size_t operator()(compressed_vector<T, B> const& s) const noexcept
+    {
+        size_t ret = 0;
+        //Fibonacci hashing
+        for (size_t i = 0; i < s.v.size(); ++i) {
+            ret ^= (size_t)(s.v[i] & ~0U) + 0x9e3779b9 + (ret << 6) + (ret >> 2);
+            ret ^= (size_t)(s.v[i] >> 32) + 0x9e3779b9 + (ret << 6) + (ret >> 2);
+        }
+        return ret;
+    }
+};
+
+#endif
-- 
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