Merge bitcoin/bitcoin#24077: util: Make base_uint::GetHex() and base_uint::SetHex() not depend on uint256

a4f4f89 Replace uint256 specific implementations of base_uint::GetHex() and base_uint::SetHex() with proper ones that don't depend on uint256 and replace template methods instantiations of base_uint with template class instantiation (Samer Afach)

Pull request description:

  The current implementations of `SetHex()` and `GetHex()` in `base_uint` use `arith_uint256`'s implementations. Which means, any attempt to create anything other than `arith_uint256` (say `arith_uint512`) and using any of these functions (which is what I needed in my application) will just not work and will cause compilation errors (besides the immediate linking errors due to templates being in source files instantiated only for 256) because there's no viable conversion from `arith_uint256` and any of the other possible types. Besides that these function will yield wrong results even if the conversion is possible depending on the size. This is fixed in this PR.

ACKs for top commit:
  laanwj:
    re-ACK a4f4f89

Tree-SHA512: 92a930fb7ddec5a5565deae2386f7d2d84645f9e8532f8d0c0178367ae081019b32eedcb59cc11028bac0cb15d9883228e016a466b1ee8fc3c6377b4df1d4180

Author: laanwj

src/arith_uint256.cpp

@@ -146,13 +146,21 @@ double base_uint<BITS>::getdouble() const
 template <unsigned int BITS>
 std::string base_uint<BITS>::GetHex() const
 {
-    return ArithToUint256(*this).GetHex();
+    base_blob<BITS> b;
+    for (int x = 0; x < this->WIDTH; ++x) {
+        WriteLE32(b.begin() + x*4, this->pn[x]);
+    }
+    return b.GetHex();
 }
 
 template <unsigned int BITS>
 void base_uint<BITS>::SetHex(const char* psz)
 {
-    *this = UintToArith256(uint256S(psz));
+    base_blob<BITS> b;
+    b.SetHex(psz);
+    for (int x = 0; x < this->WIDTH; ++x) {
+        this->pn[x] = ReadLE32(b.begin() + x*4);
+    }
 }
 
 template <unsigned int BITS>
@@ -164,7 +172,7 @@ void base_uint<BITS>::SetHex(const std::string& str)
 template <unsigned int BITS>
 std::string base_uint<BITS>::ToString() const
 {
-    return (GetHex());
+    return GetHex();
 }
 
 template <unsigned int BITS>
@@ -183,20 +191,7 @@ unsigned int base_uint<BITS>::bits() const
 }
 
 // Explicit instantiations for base_uint<256>
-template base_uint<256>::base_uint(const std::string&);
-template base_uint<256>& base_uint<256>::operator<<=(unsigned int);
-template base_uint<256>& base_uint<256>::operator>>=(unsigned int);
-template base_uint<256>& base_uint<256>::operator*=(uint32_t b32);
-template base_uint<256>& base_uint<256>::operator*=(const base_uint<256>& b);
-template base_uint<256>& base_uint<256>::operator/=(const base_uint<256>& b);
-template int base_uint<256>::CompareTo(const base_uint<256>&) const;
-template bool base_uint<256>::EqualTo(uint64_t) const;
-template double base_uint<256>::getdouble() const;
-template std::string base_uint<256>::GetHex() const;
-template std::string base_uint<256>::ToString() const;
-template void base_uint<256>::SetHex(const char*);
-template void base_uint<256>::SetHex(const std::string&);
-template unsigned int base_uint<256>::bits() const;
+template class base_uint<256>;
 
 // This implementation directly uses shifts instead of going
 // through an intermediate MPI representation.

src/arith_uint256.h

@@ -284,4 +284,6 @@ class arith_uint256 : public base_uint<256> {
 uint256 ArithToUint256(const arith_uint256 &);
 arith_uint256 UintToArith256(const uint256 &);
 
+extern template class base_uint<256>;
+
 #endif // BITCOIN_ARITH_UINT256_H