Merge bitcoin/bitcoin#21848: refactor: Make CFeeRate constructor architecture-independent

fafd121026 refactor: Make CFeeRate constructor architecture-independent (MarcoFalke)

Pull request description:

  Currently the constructor is architecture dependent. This is confusing for several reasons:

  * It is impossible to create a transaction larger than the max value of `uint32_t`, so a 64-bit `size_t` is not needed
  * Policy (and consensus) code should be arch-independent
  * The current code will print spurious compile errors when compiled on 32-bit systems:

  ```
  policy/feerate.cpp:23:22: warning: result of comparison of constant 9223372036854775807 with expression of type 'size_t' (aka 'unsigned int') is always true [-Wtautological-constant-out-of-range-compare]
      assert(nBytes_ <= uint64_t(std::numeric_limits<int64_t>::max()));
  ```

  Fix all issues by making it arch-independent. Also, fix `{}` style according to dev notes.

ACKs for top commit:
  theStack:
    re-ACK fafd121026
  promag:
    Code review ACK fafd121026.

Tree-SHA512: e16f75bad9ee8088b87e873906d9b5633449417a6996a226a2f37d33a2b7d4f2fd91df68998a77e52163de20b40c57fadabe7fe3502e599cbb98494178591833

src/policy/feerate.cpp

@@ -7,29 +7,26 @@
 
 #include <tinyformat.h>
 
-CFeeRate::CFeeRate(const CAmount& nFeePaid, size_t nBytes_)
+CFeeRate::CFeeRate(const CAmount& nFeePaid, uint32_t num_bytes)
 {
-    assert(nBytes_ <= uint64_t(std::numeric_limits<int64_t>::max()));
-    int64_t nSize = int64_t(nBytes_);
+    const int64_t nSize{num_bytes};
 
-    if (nSize > 0)
+    if (nSize > 0) {
         nSatoshisPerK = nFeePaid * 1000 / nSize;
-    else
+    } else {
         nSatoshisPerK = 0;
+    }
 }
 
-CAmount CFeeRate::GetFee(size_t nBytes_) const
+CAmount CFeeRate::GetFee(uint32_t num_bytes) const
 {
-    assert(nBytes_ <= uint64_t(std::numeric_limits<int64_t>::max()));
-    int64_t nSize = int64_t(nBytes_);
+    const int64_t nSize{num_bytes};
 
     CAmount nFee = nSatoshisPerK * nSize / 1000;
 
     if (nFee == 0 && nSize != 0) {
-        if (nSatoshisPerK > 0)
-            nFee = CAmount(1);
-        if (nSatoshisPerK < 0)
-            nFee = CAmount(-1);
+        if (nSatoshisPerK > 0) nFee = CAmount(1);
+        if (nSatoshisPerK < 0) nFee = CAmount(-1);
     }
 
     return nFee;

src/policy/feerate.h

@@ -39,20 +39,17 @@ public:
         // We've previously had bugs creep in from silent double->int conversion...
         static_assert(std::is_integral<I>::value, "CFeeRate should be used without floats");
     }
-    /** Constructor for a fee rate in satoshis per kvB (sat/kvB). The size in bytes must not exceed (2^63 - 1).
+    /** Constructor for a fee rate in satoshis per kvB (sat/kvB).
      *
-     *  Passing an nBytes value of COIN (1e8) returns a fee rate in satoshis per vB (sat/vB),
+     *  Passing a num_bytes value of COIN (1e8) returns a fee rate in satoshis per vB (sat/vB),
      *  e.g. (nFeePaid * 1e8 / 1e3) == (nFeePaid / 1e5),
      *  where 1e5 is the ratio to convert from BTC/kvB to sat/vB.
-     *
-     *  @param[in] nFeePaid  CAmount fee rate to construct with
-     *  @param[in] nBytes    size_t bytes (units) to construct with
      */
-    CFeeRate(const CAmount& nFeePaid, size_t nBytes);
+    CFeeRate(const CAmount& nFeePaid, uint32_t num_bytes);
     /**
      * Return the fee in satoshis for the given size in bytes.
      */
-    CAmount GetFee(size_t nBytes) const;
+    CAmount GetFee(uint32_t num_bytes) const;
     /**
      * Return the fee in satoshis for a size of 1000 bytes
      */

src/test/amount_tests.cpp

@@ -83,7 +83,7 @@ BOOST_AUTO_TEST_CASE(GetFeeTest)
     BOOST_CHECK(CFeeRate(CAmount(26), 789) == CFeeRate(32));
     BOOST_CHECK(CFeeRate(CAmount(27), 789) == CFeeRate(34));
     // Maximum size in bytes, should not crash
-    CFeeRate(MAX_MONEY, std::numeric_limits<size_t>::max() >> 1).GetFeePerK();
+    CFeeRate(MAX_MONEY, std::numeric_limits<uint32_t>::max()).GetFeePerK();
 }
 
 BOOST_AUTO_TEST_CASE(BinaryOperatorTest)

src/test/fuzz/fee_rate.cpp

@@ -20,8 +20,8 @@ FUZZ_TARGET(fee_rate)
     const CFeeRate fee_rate{satoshis_per_k};
 
     (void)fee_rate.GetFeePerK();
-    const size_t bytes = fuzzed_data_provider.ConsumeIntegral<size_t>();
-    if (!MultiplicationOverflow(static_cast<int64_t>(bytes), satoshis_per_k) && bytes <= static_cast<uint64_t>(std::numeric_limits<int64_t>::max())) {
+    const auto bytes = fuzzed_data_provider.ConsumeIntegral<uint32_t>();
+    if (!MultiplicationOverflow(int64_t{bytes}, satoshis_per_k)) {
         (void)fee_rate.GetFee(bytes);
     }
     (void)fee_rate.ToString();