uint256->arith_uint256 blob256->uint256

Introduce new opaque implementation of `uint256`, move old
"arithmetic" implementation to `arith_uint256.

1 files changed, 72 insertions, 267 deletions

diff --git a/src/uint256.h b/src/uint256.h
index 8189b27cb3..6d016ab164 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -13,217 +13,37 @@
 #include <string>
 #include <vector>
 
-class uint_error : public std::runtime_error {
-public:
-    explicit uint_error(const std::string& str) : std::runtime_error(str) {}
-};
-
-/** Template base class for unsigned big integers. */
+/** Template base class for fixed-sized opaque blobs. */
 template<unsigned int BITS>
-class base_uint
+class base_blob
 {
 protected:
-    enum { WIDTH=BITS/32 };
-    uint32_t pn[WIDTH];
+    enum { WIDTH=BITS/8 };
+    uint8_t data[WIDTH];
 public:
-
-    base_uint()
+    base_blob()
     {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = 0;
+        memset(data, 0, sizeof(data));
     }
 
-    base_uint(const base_uint& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-    }
-
-    base_uint& operator=(const base_uint& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-        return *this;
-    }
+    explicit base_blob(const std::vector<unsigned char>& vch);
 
-    base_uint(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
-    }
-
-    explicit base_uint(const std::string& str);
-    explicit base_uint(const std::vector<unsigned char>& vch);
-
-    bool operator!() const
+    bool IsNull() const
     {
         for (int i = 0; i < WIDTH; i++)
-            if (pn[i] != 0)
+            if (data[i] != 0)
                 return false;
         return true;
     }
 
-    const base_uint operator~() const
-    {
-        base_uint ret;
-        for (int i = 0; i < WIDTH; i++)
-            ret.pn[i] = ~pn[i];
-        return ret;
-    }
-
-    const base_uint operator-() const
-    {
-        base_uint ret;
-        for (int i = 0; i < WIDTH; i++)
-            ret.pn[i] = ~pn[i];
-        ret++;
-        return ret;
-    }
-
-    double getdouble() const;
-
-    base_uint& operator=(uint64_t b)
-    {
-        pn[0] = (unsigned int)b;
-        pn[1] = (unsigned int)(b >> 32);
-        for (int i = 2; i < WIDTH; i++)
-            pn[i] = 0;
-        return *this;
-    }
-
-    base_uint& operator^=(const base_uint& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] ^= b.pn[i];
-        return *this;
-    }
-
-    base_uint& operator&=(const base_uint& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] &= b.pn[i];
-        return *this;
-    }
-
-    base_uint& operator|=(const base_uint& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] |= b.pn[i];
-        return *this;
-    }
-
-    base_uint& operator^=(uint64_t b)
-    {
-        pn[0] ^= (unsigned int)b;
-        pn[1] ^= (unsigned int)(b >> 32);
-        return *this;
-    }
-
-    base_uint& operator|=(uint64_t b)
-    {
-        pn[0] |= (unsigned int)b;
-        pn[1] |= (unsigned int)(b >> 32);
-        return *this;
-    }
-
-    base_uint& operator<<=(unsigned int shift);
-    base_uint& operator>>=(unsigned int shift);
-
-    base_uint& operator+=(const base_uint& b)
-    {
-        uint64_t carry = 0;
-        for (int i = 0; i < WIDTH; i++)
-        {
-            uint64_t n = carry + pn[i] + b.pn[i];
-            pn[i] = n & 0xffffffff;
-            carry = n >> 32;
-        }
-        return *this;
-    }
-
-    base_uint& operator-=(const base_uint& b)
-    {
-        *this += -b;
-        return *this;
-    }
-
-    base_uint& operator+=(uint64_t b64)
-    {
-        base_uint b;
-        b = b64;
-        *this += b;
-        return *this;
-    }
-
-    base_uint& operator-=(uint64_t b64)
-    {
-        base_uint b;
-        b = b64;
-        *this += -b;
-        return *this;
-    }
-
-    base_uint& operator*=(uint32_t b32);
-    base_uint& operator*=(const base_uint& b);
-    base_uint& operator/=(const base_uint& b);
-
-    base_uint& operator++()
-    {
-        // prefix operator
-        int i = 0;
-        while (++pn[i] == 0 && i < WIDTH-1)
-            i++;
-        return *this;
-    }
-
-    const base_uint operator++(int)
-    {
-        // postfix operator
-        const base_uint ret = *this;
-        ++(*this);
-        return ret;
-    }
-
-    base_uint& operator--()
-    {
-        // prefix operator
-        int i = 0;
-        while (--pn[i] == (uint32_t)-1 && i < WIDTH-1)
-            i++;
-        return *this;
-    }
-
-    const base_uint operator--(int)
+    void SetNull()
     {
-        // postfix operator
-        const base_uint ret = *this;
-        --(*this);
-        return ret;
+        memset(data, 0, sizeof(data));
     }
 
-    int CompareTo(const base_uint& b) const;
-    bool EqualTo(uint64_t b) const;
-
-    friend inline const base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
-    friend inline const base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
-    friend inline const base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
-    friend inline const base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
-    friend inline const base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
-    friend inline const base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
-    friend inline const base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
-    friend inline const base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
-    friend inline const base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
-    friend inline const base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
-    friend inline bool operator==(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) == 0; }
-    friend inline bool operator!=(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) != 0; }
-    friend inline bool operator>(const base_uint& a, const base_uint& b) { return a.CompareTo(b) > 0; }
-    friend inline bool operator<(const base_uint& a, const base_uint& b) { return a.CompareTo(b) < 0; }
-    friend inline bool operator>=(const base_uint& a, const base_uint& b) { return a.CompareTo(b) >= 0; }
-    friend inline bool operator<=(const base_uint& a, const base_uint& b) { return a.CompareTo(b) <= 0; }
-    friend inline bool operator==(const base_uint& a, uint64_t b) { return a.EqualTo(b); }
-    friend inline bool operator!=(const base_uint& a, uint64_t b) { return !a.EqualTo(b); }
+    friend inline bool operator==(const base_blob& a, const base_blob& b) { return memcmp(a.data, b.data, sizeof(a.data)) == 0; }
+    friend inline bool operator!=(const base_blob& a, const base_blob& b) { return memcmp(a.data, b.data, sizeof(a.data)) != 0; }
+    friend inline bool operator<(const base_blob& a, const base_blob& b) { return memcmp(a.data, b.data, sizeof(a.data)) < 0; }
 
     std::string GetHex() const;
     void SetHex(const char* psz);
@@ -232,122 +52,107 @@ public:
 
     unsigned char* begin()
     {
-        return (unsigned char*)&pn[0];
+        return &data[0];
     }
 
     unsigned char* end()
     {
-        return (unsigned char*)&pn[WIDTH];
+        return &data[WIDTH];
     }
 
     const unsigned char* begin() const
     {
-        return (unsigned char*)&pn[0];
+        return &data[0];
     }
 
     const unsigned char* end() const
     {
-        return (unsigned char*)&pn[WIDTH];
+        return &data[WIDTH];
     }
 
     unsigned int size() const
     {
-        return sizeof(pn);
-    }
-
-    /**
-     * Returns the position of the highest bit set plus one, or zero if the
-     * value is zero.
-     */
-    unsigned int bits() const;
-
-    uint64_t GetLow64() const
-    {
-        assert(WIDTH >= 2);
-        return pn[0] | (uint64_t)pn[1] << 32;
+        return sizeof(data);
     }
 
     unsigned int GetSerializeSize(int nType, int nVersion) const
     {
-        return sizeof(pn);
+        return sizeof(data);
     }
 
     template<typename Stream>
     void Serialize(Stream& s, int nType, int nVersion) const
     {
-        s.write((char*)pn, sizeof(pn));
+        s.write((char*)data, sizeof(data));
     }
 
     template<typename Stream>
     void Unserialize(Stream& s, int nType, int nVersion)
     {
-        s.read((char*)pn, sizeof(pn));
-    }
-
-    // Temporary for migration to opaque uint160/256
-    uint64_t GetCheapHash() const
-    {
-        return GetLow64();
-    }
-    void SetNull()
-    {
-        memset(pn, 0, sizeof(pn));
-    }
-    bool IsNull() const
-    {
-        for (int i = 0; i < WIDTH; i++)
-            if (pn[i] != 0)
-                return false;
-        return true;
+        s.read((char*)data, sizeof(data));
     }
 };
 
-/** 160-bit unsigned big integer. */
-class uint160 : public base_uint<160> {
+/** 160-bit opaque blob.
+ * @note This type is called uint160 for historical reasons only. It is an opaque
+ * blob of 160 bits and has no integer operations.
+ */
+class uint160 : public base_blob<160> {
 public:
     uint160() {}
-    uint160(const base_uint<160>& b) : base_uint<160>(b) {}
-    uint160(uint64_t b) : base_uint<160>(b) {}
-    explicit uint160(const std::string& str) : base_uint<160>(str) {}
-    explicit uint160(const std::vector<unsigned char>& vch) : base_uint<160>(vch) {}
+    uint160(const base_blob<160>& b) : base_blob<160>(b) {}
+    explicit uint160(const std::vector<unsigned char>& vch) : base_blob<160>(vch) {}
 };
 
-/** 256-bit unsigned big integer. */
-class uint256 : public base_uint<256> {
+/** 256-bit opaque blob.
+ * @note This type is called uint256 for historical reasons only. It is an
+ * opaque blob of 256 bits and has no integer operations. Use arith_uint256 if
+ * those are required.
+ */
+class uint256 : public base_blob<256> {
 public:
     uint256() {}
-    uint256(const base_uint<256>& b) : base_uint<256>(b) {}
-    uint256(uint64_t b) : base_uint<256>(b) {}
-    explicit uint256(const std::string& str) : base_uint<256>(str) {}
-    explicit uint256(const std::vector<unsigned char>& vch) : base_uint<256>(vch) {}
-    
-    /**
-     * The "compact" format is a representation of a whole
-     * number N using an unsigned 32bit number similar to a
-     * floating point format.
-     * The most significant 8 bits are the unsigned exponent of base 256.
-     * This exponent can be thought of as "number of bytes of N".
-     * The lower 23 bits are the mantissa.
-     * Bit number 24 (0x800000) represents the sign of N.
-     * N = (-1^sign) * mantissa * 256^(exponent-3)
-     * 
-     * Satoshi's original implementation used BN_bn2mpi() and BN_mpi2bn().
-     * MPI uses the most significant bit of the first byte as sign.
-     * Thus 0x1234560000 is compact (0x05123456)
-     * and  0xc0de000000 is compact (0x0600c0de)
-     * 
-     * Bitcoin only uses this "compact" format for encoding difficulty
-     * targets, which are unsigned 256bit quantities.  Thus, all the
-     * complexities of the sign bit and using base 256 are probably an
-     * implementation accident.
+    uint256(const base_blob<256>& b) : base_blob<256>(b) {}
+    explicit uint256(const std::vector<unsigned char>& vch) : base_blob<256>(vch) {}
+
+    /** A cheap hash function that just returns 64 bits from the result, it can be
+     * used when the contents are considered uniformly random. It is not appropriate
+     * when the value can easily be influenced from outside as e.g. a network adversary could
+     * provide values to trigger worst-case behavior.
+     * @note The result of this function is not stable between little and big endian.
      */
-    uint256& SetCompact(uint32_t nCompact, bool *pfNegative = NULL, bool *pfOverflow = NULL);
-    uint32_t GetCompact(bool fNegative = false) const;
+    uint64_t GetCheapHash() const
+    {
+        uint64_t result;
+        memcpy((void*)&result, (void*)data, 8);
+        return result;
+    }
 
+    /** A more secure, salted hash function.
+     * @note This hash is not stable between little and big endian.
+     */
     uint64_t GetHash(const uint256& salt) const;
 };
 
-// Temporary for migration to opaque uint160/256
-inline uint256 uint256S(const std::string &x) { return uint256(x); }
+/* uint256 from const char *.
+ * This is a separate function because the constructor uint256(const char*) can result
+ * in dangerously catching uint256(0).
+ */
+inline uint256 uint256S(const char *str)
+{
+    uint256 rv;
+    rv.SetHex(str);
+    return rv;
+}
+/* uint256 from std::string.
+ * This is a separate function because the constructor uint256(const std::string &str) can result
+ * in dangerously catching uint256(0) via std::string(const char*).
+ */
+inline uint256 uint256S(const std::string& str)
+{
+    uint256 rv;
+    rv.SetHex(str);
+    return rv;
+}
 
 #endif // BITCOIN_UINT256_H