Generalize ConvertBits

Author: sipa

src/key_io.cpp

@@ -43,14 +43,14 @@ class DestinationEncoder : public boost::static_visitor<std::string>
     std::string operator()(const WitnessV0KeyHash& id) const
     {
         std::vector<unsigned char> data = {0};
-        ConvertBits<8, 5, true>(data, id.begin(), id.end());
+        ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, id.begin(), id.end());
         return bech32::Encode(m_params.Bech32HRP(), data);
     }
 
     std::string operator()(const WitnessV0ScriptHash& id) const
     {
         std::vector<unsigned char> data = {0};
-        ConvertBits<8, 5, true>(data, id.begin(), id.end());
+        ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, id.begin(), id.end());
         return bech32::Encode(m_params.Bech32HRP(), data);
     }
 
@@ -60,7 +60,7 @@ class DestinationEncoder : public boost::static_visitor<std::string>
             return {};
         }
         std::vector<unsigned char> data = {(unsigned char)id.version};
-        ConvertBits<8, 5, true>(data, id.program, id.program + id.length);
+        ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, id.program, id.program + id.length);
         return bech32::Encode(m_params.Bech32HRP(), data);
     }
 
@@ -94,7 +94,7 @@ CTxDestination DecodeDestination(const std::string& str, const CChainParams& par
         // Bech32 decoding
         int version = bech.second[0]; // The first 5 bit symbol is the witness version (0-16)
         // The rest of the symbols are converted witness program bytes.
-        if (ConvertBits<5, 8, false>(data, bech.second.begin() + 1, bech.second.end())) {
+        if (ConvertBits<5, 8, false>([&](unsigned char c) { data.push_back(c); }, bech.second.begin() + 1, bech.second.end())) {
             if (version == 0) {
                 {
                     WitnessV0KeyHash keyid;

src/utilstrencodings.h

@@ -151,7 +151,7 @@ bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out);
 
 /** Convert from one power-of-2 number base to another. */
 template<int frombits, int tobits, bool pad, typename O, typename I>
-bool ConvertBits(O& out, I it, I end) {
+bool ConvertBits(const O& outfn, I it, I end) {
     size_t acc = 0;
     size_t bits = 0;
     constexpr size_t maxv = (1 << tobits) - 1;
@@ -161,12 +161,12 @@ bool ConvertBits(O& out, I it, I end) {
         bits += frombits;
         while (bits >= tobits) {
             bits -= tobits;
-            out.push_back((acc >> bits) & maxv);
+            outfn((acc >> bits) & maxv);
         }
         ++it;
     }
     if (pad) {
-        if (bits) out.push_back((acc << (tobits - bits)) & maxv);
+        if (bits) outfn((acc << (tobits - bits)) & maxv);
     } else if (bits >= frombits || ((acc << (tobits - bits)) & maxv)) {
         return false;
     }