Remove bounds check for NewAmount.

Amount should still be a usable type even if the monetary amount being
described is not an amount at a single instance in time, for example,
the total of all BTC received by an address.  Therefore, the bounds
checks that the amount is within the total amount of bitcoin ever
producable have been removed.

The checks for NaN and +-Infinity remain.

amount.go

@@ -54,20 +54,23 @@ func (u AmountUnit) String() string {
 type Amount int64
 
 // NewAmount creates an Amount from a floating point value representing
-// some value in bitcoin.
+// some value in bitcoin.  NewAmount errors if f is NaN or +-Infinity, but
+// does not check that the amount is within the total amount of bitcoin
+// producable as f may not refer to an amount at a single moment in time.
 func NewAmount(f float64) (Amount, error) {
-	a := f * float64(SatoshiPerBitcoin)
+	// The amount is only considered invalid if it cannot be represented
-
+	// as an integer type.  This may happen if f is NaN or +-Infinity.
-	// The amount is only valid if it does not exceed the total amount
+	switch {
-	// of bitcoin producable, and is not a floating point number that
+	case math.IsNaN(f):
-	// would otherwise fail that check such as NaN or +-Inf.
-	switch abs := math.Abs(a); {
-	case abs > float64(MaxSatoshi):
 		fallthrough
-	case math.IsNaN(abs) || math.IsInf(abs, 1):
+	case math.IsInf(f, 1):
+		fallthrough
+	case math.IsInf(f, -1):
 		return 0, errors.New("invalid bitcoin amount")
 	}
 
+	a := f * float64(SatoshiPerBitcoin)
+
 	// Depending on the sign, add or subtract 0.5 and rely on integer
 	// truncation to correctly round the value up or down.
 	if a < 0 {

amount_test.go

@@ -25,17 +25,29 @@ func TestAmountCreation(t *testing.T) {
 			expected: 0,
 		},
 		{
-			name:     "max",
+			name:     "max producable",
 			amount:   21e6,
 			valid:    true,
 			expected: Amount(MaxSatoshi),
 		},
 		{
-			name:     "min",
+			name:     "min producable",
 			amount:   -21e6,
 			valid:    true,
 			expected: Amount(-MaxSatoshi),
 		},
+		{
+			name:     "exceeds max producable",
+			amount:   21e6 + 1e-8,
+			valid:    true,
+			expected: Amount(MaxSatoshi + 1),
+		},
+		{
+			name:     "exceeds min producable",
+			amount:   -21e6 - 1e-8,
+			valid:    true,
+			expected: Amount(-MaxSatoshi - 1),
+		},
 		{
 			name:     "one hundred",
 			amount:   100,
@@ -62,16 +74,6 @@ func TestAmountCreation(t *testing.T) {
 		},
 
 		// Negative tests.
-		{
-			name:   "exceeds max",
-			amount: 21e6 + 1,
-			valid:  false,
-		},
-		{
-			name:   "exceeds min",
-			amount: -21e6 - 1,
-			valid:  false,
-		},
 		{
 			name:   "not-a-number",
 			amount: math.NaN(),

test_coverage.txt

@@ -3,20 +3,20 @@ github.com/conformal/btcutil/base58.go	 Base58Decode			 100.00% (20/20)
 github.com/conformal/btcutil/base58.go	 Base58Encode			 100.00% (15/15)
 github.com/conformal/btcutil/block.go	 Block.Tx			 100.00% (12/12)
 github.com/conformal/btcutil/block.go	 Block.Transactions		 100.00% (11/11)
+github.com/conformal/btcutil/amount.go	 NewAmount			 100.00% (9/9)
 github.com/conformal/btcutil/address.go	 encodeAddress			 100.00% (9/9)
 github.com/conformal/btcutil/amount.go	 AmountUnit.String		 100.00% (8/8)
-github.com/conformal/btcutil/amount.go	 NewAmount			 100.00% (8/8)
 github.com/conformal/btcutil/block.go	 NewBlockFromBytes		 100.00% (7/7)
 github.com/conformal/btcutil/tx.go	 NewTxFromBytes			 100.00% (7/7)
-github.com/conformal/btcutil/block.go	 Block.Sha			 100.00% (5/5)
 github.com/conformal/btcutil/tx.go	 Tx.Sha				 100.00% (5/5)
+github.com/conformal/btcutil/address.go	 checkBitcoinNet		 100.00% (5/5)
+github.com/conformal/btcutil/block.go	 Block.Sha			 100.00% (5/5)
 github.com/conformal/btcutil/amount.go	 Amount.Format			 100.00% (2/2)
 github.com/conformal/btcutil/address.go	 NewAddressScriptHash		 100.00% (2/2)
 github.com/conformal/btcutil/hash160.go	 calcHash			 100.00% (2/2)
 github.com/conformal/btcutil/block.go	 Block.MsgBlock			 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 AddressPubKeyHash.EncodeAddress 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 AddressPubKeyHash.ScriptAddress 100.00% (1/1)
-github.com/conformal/btcutil/address.go	 AddressPubKeyHash.String	 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 AddressScriptHash.EncodeAddress 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 AddressScriptHash.ScriptAddress 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 AddressScriptHash.String	 100.00% (1/1)
@@ -35,25 +35,25 @@ github.com/conformal/btcutil/tx.go	 Tx.MsgTx			 100.00% (1/1)
 github.com/conformal/btcutil/tx.go	 Tx.Index			 100.00% (1/1)
 github.com/conformal/btcutil/tx.go	 Tx.SetIndex			 100.00% (1/1)
 github.com/conformal/btcutil/tx.go	 NewTx				 100.00% (1/1)
+github.com/conformal/btcutil/address.go	 AddressPubKeyHash.String	 100.00% (1/1)
 github.com/conformal/btcutil/address.go	 DecodeAddress			 95.65% (22/23)
 github.com/conformal/btcutil/appdata.go	 appDataDir			 92.00% (23/25)
 github.com/conformal/btcutil/address.go	 NewAddressScriptHashFromHash	 91.67% (11/12)
 github.com/conformal/btcutil/address.go	 NewAddressPubKeyHash		 91.67% (11/12)
 github.com/conformal/btcutil/address.go	 EncodePrivateKey		 90.91% (20/22)
-github.com/conformal/btcutil/block.go	 Block.Bytes			 88.89% (8/9)
 github.com/conformal/btcutil/block.go	 Block.TxLoc			 88.89% (8/9)
+github.com/conformal/btcutil/block.go	 Block.Bytes			 88.89% (8/9)
 github.com/conformal/btcutil/address.go	 AddressPubKey.serialize	 85.71% (6/7)
 github.com/conformal/btcutil/address.go	 DecodePrivateKey		 83.33% (20/24)
 github.com/conformal/btcutil/address.go	 NewAddressPubKey		 83.33% (15/18)
-github.com/conformal/btcutil/address.go	 checkBitcoinNet		 83.33% (5/6)
 github.com/conformal/btcutil/block.go	 Block.TxSha			 75.00% (3/4)
-github.com/conformal/btcutil/address.go	 AddressScriptHash.IsForNet	 60.00% (3/5)
-github.com/conformal/btcutil/address.go	 AddressPubKeyHash.IsForNet	 60.00% (3/5)
 github.com/conformal/btcutil/address.go	 AddressPubKey.IsForNet		 60.00% (3/5)
+github.com/conformal/btcutil/address.go	 AddressPubKeyHash.IsForNet	 60.00% (3/5)
+github.com/conformal/btcutil/address.go	 AddressScriptHash.IsForNet	 60.00% (3/5)
 github.com/conformal/btcutil/certgen.go	 NewTLSCertPair			 0.00% (0/50)
 github.com/conformal/btcutil/address.go	 AddressPubKey.AddressPubKeyHash 0.00% (0/3)
 github.com/conformal/btcutil/appdata.go	 AppDataDir			 0.00% (0/1)
-github.com/conformal/btcutil/address.go	 AddressPubKey.Format		 0.00% (0/1)
 github.com/conformal/btcutil/address.go	 AddressPubKey.SetFormat	 0.00% (0/1)
-github.com/conformal/btcutil		 ------------------------------- 78.51% (296/377)
+github.com/conformal/btcutil/address.go	 AddressPubKey.Format		 0.00% (0/1)
+github.com/conformal/btcutil		 ------------------------------- 78.78% (297/377)