util: Avoid invalid integer negation in ValueFromAmount: make ValueFromAmount(const CAmount& n) well-defined also when n is std::numeric_limits<CAmount>::min()

Author: practicalswift

src/core_io.h

@@ -40,7 +40,7 @@ std::vector<unsigned char> ParseHexUV(const UniValue& v, const std::string& strN
 int ParseSighashString(const UniValue& sighash);
 
 // core_write.cpp
-UniValue ValueFromAmount(const CAmount& amount);
+UniValue ValueFromAmount(const CAmount amount);
 std::string FormatScript(const CScript& script);
 std::string EncodeHexTx(const CTransaction& tx, const int serializeFlags = 0);
 std::string SighashToStr(unsigned char sighash_type);

src/core_write.cpp

@@ -14,17 +14,20 @@
 #include <undo.h>
 #include <univalue.h>
 #include <util/check.h>
-#include <util/system.h>
 #include <util/strencodings.h>
+#include <util/system.h>
 
-UniValue ValueFromAmount(const CAmount& amount)
+UniValue ValueFromAmount(const CAmount amount)
 {
-    bool sign = amount < 0;
-    int64_t n_abs = (sign ? -amount : amount);
-    int64_t quotient = n_abs / COIN;
-    int64_t remainder = n_abs % COIN;
+    static_assert(COIN > 1);
+    int64_t quotient = amount / COIN;
+    int64_t remainder = amount % COIN;
+    if (amount < 0) {
+        quotient = -quotient;
+        remainder = -remainder;
+    }
     return UniValue(UniValue::VNUM,
-            strprintf("%s%d.%08d", sign ? "-" : "", quotient, remainder));
+            strprintf("%s%d.%08d", amount < 0 ? "-" : "", quotient, remainder));
 }
 
 std::string FormatScript(const CScript& script)

src/test/fuzz/integer.cpp

@@ -131,8 +131,7 @@ FUZZ_TARGET_INIT(integer, initialize_integer)
     (void)SipHashUint256Extra(u64, u64, u256, u32);
     (void)ToLower(ch);
     (void)ToUpper(ch);
-    // ValueFromAmount(i) not defined when i == std::numeric_limits<int64_t>::min()
-    if (i64 != std::numeric_limits<int64_t>::min()) {
+    {
         int64_t parsed_money;
         if (ParseMoney(ValueFromAmount(i64).getValStr(), parsed_money)) {
             assert(parsed_money == i64);

src/test/fuzz/transaction.cpp

@@ -100,16 +100,7 @@ FUZZ_TARGET_INIT(transaction, initialize_transaction)
     (void)IsWitnessStandard(tx, coins_view_cache);
 
     UniValue u(UniValue::VOBJ);
-    // ValueFromAmount(i) not defined when i == std::numeric_limits<int64_t>::min()
-    bool skip_tx_to_univ = false;
-    for (const CTxOut& txout : tx.vout) {
-        if (txout.nValue == std::numeric_limits<int64_t>::min()) {
-            skip_tx_to_univ = true;
-        }
-    }
-    if (!skip_tx_to_univ) {
-        TxToUniv(tx, /* hashBlock */ {}, u);
-        static const uint256 u256_max(uint256S("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"));
-        TxToUniv(tx, u256_max, u);
-    }
+    TxToUniv(tx, /* hashBlock */ {}, u);
+    static const uint256 u256_max(uint256S("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"));
+    TxToUniv(tx, u256_max, u);
 }

src/test/rpc_tests.cpp

@@ -174,6 +174,16 @@ BOOST_AUTO_TEST_CASE(rpc_format_monetary_values)
     BOOST_CHECK_EQUAL(ValueFromAmount(COIN/1000000).write(), "0.00000100");
     BOOST_CHECK_EQUAL(ValueFromAmount(COIN/10000000).write(), "0.00000010");
     BOOST_CHECK_EQUAL(ValueFromAmount(COIN/100000000).write(), "0.00000001");
+
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::max()).write(), "92233720368.54775807");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::max() - 1).write(), "92233720368.54775806");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::max() - 2).write(), "92233720368.54775805");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::max() - 3).write(), "92233720368.54775804");
+    // ...
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::min() + 3).write(), "-92233720368.54775805");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::min() + 2).write(), "-92233720368.54775806");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::min() + 1).write(), "-92233720368.54775807");
+    BOOST_CHECK_EQUAL(ValueFromAmount(std::numeric_limits<CAmount>::min()).write(), "-92233720368.54775808");
 }
 
 static UniValue ValueFromString(const std::string &str)