crypto: add IsEmptySet method to MuHash3072 class

Author: theStack

src/crypto/muhash.cpp

@@ -573,6 +573,15 @@ MuHash3072& MuHash3072::operator/=(const MuHash3072& div) noexcept
     return *this;
 }
 
+bool MuHash3072::IsEmptySet() noexcept
+{
+    unsigned char num_bytes[Num3072::BYTE_SIZE];
+    unsigned char den_bytes[Num3072::BYTE_SIZE];
+    m_numerator.ToBytes(num_bytes);
+    m_denominator.ToBytes(den_bytes);
+    return std::equal(std::begin(num_bytes), std::end(num_bytes), std::begin(den_bytes));
+}
+
 MuHash3072& MuHash3072::Insert(Span<const unsigned char> in) noexcept {
     m_numerator.Multiply(ToNum3072(in));
     return *this;

src/crypto/muhash.h

@@ -123,6 +123,9 @@ class MuHash3072
     /* Divide (resulting in a hash for the difference of the sets) */
     MuHash3072& operator/=(const MuHash3072& div) noexcept;
 
+    /* Check if the set is empty. */
+    bool IsEmptySet() noexcept;
+
     /* Finalize into a 32-byte hash. Does not change this object's value. */
     void Finalize(uint256& out) noexcept;