Merge rust-bitcoin/rust-bitcoin#1870: Add from_int_btc method to Amount

9f7449b572 Use from_int_btc function for const context (yancy)
f93e67977a Add from_int_btc function to Amount (yancy)

Pull request description:

  Followup PR from https://github.com/rust-bitcoin/rust-bitcoin/pull/1811

  Added a `const` associated function `from_int_btc()` for Amount.  `panic()` in const context is only available after 1.57+ so a work around is provided.

ACKs for top commit:
  tcharding:
    ACK 9f7449b572
  apoelstra:
    ACK 9f7449b572

Tree-SHA512: 7755234f2e573577d754f0224083cb7acc059e58833790fe344b0d9bad0acd89b0f74054d9efcba2133576222c7e9ab8dc3d81ddc10fbdcd4f83638d697118c4

bitcoin/examples/taproot-psbt.rs

@@ -49,7 +49,7 @@ const UTXO_1: P2trUtxo = P2trUtxo {
     script_pubkey: UTXO_SCRIPT_PUBKEY,
     pubkey: UTXO_PUBKEY,
     master_fingerprint: UTXO_MASTER_FINGERPRINT,
-    amount_in_sats: Amount::from_sat(50 * 100_000_000), // 50 BTC
+    amount_in_sats: Amount::from_int_btc(50),
     derivation_path: BIP86_DERIVATION_PATH,
 };
 
@@ -60,7 +60,7 @@ const UTXO_2: P2trUtxo = P2trUtxo {
     script_pubkey: UTXO_SCRIPT_PUBKEY,
     pubkey: UTXO_PUBKEY,
     master_fingerprint: UTXO_MASTER_FINGERPRINT,
-    amount_in_sats: Amount::from_sat(50 * 100_000_000), // 50 BTC
+    amount_in_sats: Amount::from_int_btc(50),
     derivation_path: BIP86_DERIVATION_PATH,
 };
 
@@ -71,7 +71,7 @@ const UTXO_3: P2trUtxo = P2trUtxo {
     script_pubkey: UTXO_SCRIPT_PUBKEY,
     pubkey: UTXO_PUBKEY,
     master_fingerprint: UTXO_MASTER_FINGERPRINT,
-    amount_in_sats: Amount::from_sat(50 * 100_000_000), // 50 BTC
+    amount_in_sats: Amount::from_int_btc(50),
     derivation_path: BIP86_DERIVATION_PATH,
 };
 

bitcoin/src/amount.rs

@@ -502,9 +502,9 @@ impl Amount {
     /// Exactly one satoshi.
     pub const ONE_SAT: Amount = Amount(1);
     /// Exactly one bitcoin.
-    pub const ONE_BTC: Amount = Amount(100_000_000);
+    pub const ONE_BTC: Amount = Self::from_int_btc(1);
     /// The maximum value allowed as an amount. Useful for sanity checking.
-    pub const MAX_MONEY: Amount = Amount(21_000_000 * 100_000_000);
+    pub const MAX_MONEY: Amount = Self::from_int_btc(21_000_000);
     /// The minimum value of an amount.
     pub const MIN: Amount = Amount::ZERO;
     /// The maximum value of an amount.
@@ -529,6 +529,28 @@ impl Amount {
         Amount::from_float_in(btc, Denomination::Bitcoin)
     }
 
+    /// Convert from a value expressing integer values of bitcoins to an [Amount]
+    /// in const context.
+    ///
+    /// ## Panics
+    ///
+    /// The function panics if the argument multiplied by the number of sats
+    /// per bitcoin overflows a u64 type.
+    pub const fn from_int_btc(btc: u64) -> Amount {
+        // TODO replace whith unwrap() when available in const context.
+        match btc.checked_mul(100_000_000) {
+            Some(amount) => Amount::from_sat(amount),
+            None => {
+                // TODO replace with panic!() when MSRV = 1.57+
+                #[allow(unconditional_panic)]
+                // disabling this lint until panic!() can be used.
+                #[allow(clippy::let_unit_value)]
+                let _int_overflow_converting_btc_to_sats = [(); 0][1];
+                Amount(0)
+            }
+        }
+    }
+
     /// Parse a decimal string as a value in the given denomination.
     ///
     /// Note: This only parses the value string.  If you want to parse a value
@@ -1589,6 +1611,16 @@ mod tests {
         }
     }
 
+    #[test]
+    fn from_int_btc() {
+        let amt = Amount::from_int_btc(2);
+        assert_eq!(Amount::from_sat(200_000_000), amt);
+    }
+
+    #[should_panic]
+    #[test]
+    fn from_int_btc_panic() { Amount::from_int_btc(u64::MAX); }
+
     #[test]
     fn mul_div() {
         let sat = Amount::from_sat;