Add comment about size calculations for converted serialized keys

src/key_io.cpp

@@ -92,6 +92,7 @@ public:
         // ConvertBits requires unsigned char, but CDataStream uses char
         std::vector<unsigned char> seraddr(ss.begin(), ss.end());
         std::vector<unsigned char> data;
+        // See calculation comment below
         data.reserve((seraddr.size() * 8 + 4) / 5);
         ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, seraddr.begin(), seraddr.end());
         return bech32::Encode(m_params.Bech32HRP(CChainParams::SAPLING_PAYMENT_ADDRESS), data);
@@ -148,6 +149,7 @@ public:
         // ConvertBits requires unsigned char, but CDataStream uses char
         std::vector<unsigned char> serkey(ss.begin(), ss.end());
         std::vector<unsigned char> data;
+        // See calculation comment below
         data.reserve((serkey.size() * 8 + 4) / 5);
         ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, serkey.begin(), serkey.end());
         std::string ret = bech32::Encode(m_params.Bech32HRP(CChainParams::SAPLING_SPENDING_KEY), data);
@@ -159,6 +161,10 @@ public:
     std::string operator()(const libzcash::InvalidEncoding& no) const { return {}; }
 };
 
+// Sizes of SaplingPaymentAddress and SaplingSpendingKey after
+// ConvertBits<8, 5, true>(). The calculations below take the
+// regular serialized size in bytes, convert to bits, and then
+// perform ceiling division to get the number of 5-bit clusters.
 const size_t ConvertedSaplingPaymentAddressSize = ((32 + 11) * 8 + 4) / 5;
 const size_t ConvertedSaplingSpendingKeySize = (32 * 8 + 4) / 5;
 } // namespace