Add multiplication and division to uint160/uint256

1 files changed, 70 insertions, 0 deletions

diff --git a/src/uint256.h b/src/uint256.h
index b6365bb36b..7b17694eb2 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -222,6 +222,57 @@ public:
         return *this;
     }
 
+    base_uint& operator*=(uint32_t b32)
+    {
+        uint64_t carry = 0;
+        for (int i = 0; i < WIDTH; i++)
+        {
+            uint64_t n = carry + (uint64_t)b32 * pn[i];
+            pn[i] = n & 0xffffffff;
+            carry = n >> 32;
+        }
+        return *this;
+    }
+
+    base_uint& operator*=(const base_uint& b)
+    {
+        base_uint a = *this;
+        *this = 0;
+        for (int j = 0; j < WIDTH; j++) {
+            uint64_t carry = 0;
+            for (int i = 0; i + j < WIDTH; i++) {
+                uint64_t n = carry + pn[i + j] + (uint64_t)a.pn[j] * b.pn[i];
+                pn[i + j] = n & 0xffffffff;
+                carry = n >> 32;
+            }
+        }
+        return *this;
+    }
+
+    base_uint& operator/=(const base_uint& b)
+    {
+        base_uint div = b; // make a copy, so we can shift.
+        base_uint num = *this; // make a copy, so we can subtract.
+        *this = 0; // the quotient.
+        int num_bits = num.bits();
+        int div_bits = div.bits();
+        if (div_bits == 0)
+            throw uint_error("Division by zero");
+        if (div_bits > num_bits) // the result is certainly 0.
+            return *this;
+        int shift = num_bits - div_bits;
+        div <<= shift; // shift so that div and nun align.
+        while (shift >= 0) {
+            if (num >= div) {
+                num -= div;
+                pn[shift / 32] |= (1 << (shift & 31)); // set a bit of the result.
+            }
+            div >>= 1; // shift back.
+            shift--;
+        }
+        // num now contains the remainder of the division.
+        return *this;
+    }
 
     base_uint& operator++()
     {
@@ -338,11 +389,14 @@ public:
 
     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; }
 
     std::string GetHex() const
     {
@@ -417,6 +471,22 @@ public:
         return sizeof(pn);
     }
 
+    // Returns the position of the highest bit set plus one, or zero if the
+    // value is zero.
+    unsigned int bits() const
+    {
+        for (int pos = WIDTH-1; pos >= 0; pos--) {
+            if (pn[pos]) {
+                for (int bits = 31; bits > 0; bits--) {
+                    if (pn[pos] & 1<<bits)
+                        return 32*pos + bits + 1;
+                }
+                return 32*pos + 1;
+            }
+        }
+        return 0;
+    }
+
     uint64_t GetLow64() const
     {
         assert(WIDTH >= 2);