benchmarks: add benchmarks for checksum param generation

Mainly to confirm that these are really expensive (on my system,
mulitple milliseconds for the descriptor checksum) and that we should
precompute these values rather than suggesting users compute them at
run-time whenever they want to do correction (which would result in a
simpler API).

Author: apoelstra

src/primitives/checksum.rs

@@ -588,3 +588,40 @@ mod tests {
         println!("{}", _s);
     }
 }
+
+#[cfg(bench)]
+mod benches {
+    use std::io::{sink, Write};
+
+    use test::{black_box, Bencher};
+
+    use crate::{Fe1024, Fe32, Fe32768, PrintImpl};
+
+    #[bench]
+    fn compute_bech32_params(bh: &mut Bencher) {
+        bh.iter(|| {
+            let im = PrintImpl::<Fe1024>::new(
+                "Bech32",
+                &[Fe32::A, Fe32::K, Fe32::_5, Fe32::_4, Fe32::A, Fe32::J],
+                &[Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::P],
+            );
+            let res = write!(sink(), "{}", im);
+            black_box(&im);
+            black_box(&res);
+        })
+    }
+
+    #[bench]
+    fn compute_descriptor_params(bh: &mut Bencher) {
+        bh.iter(|| {
+            let im = PrintImpl::<Fe32768>::new(
+                "DescriptorChecksum",
+                &[Fe32::_7, Fe32::H, Fe32::_0, Fe32::W, Fe32::_2, Fe32::X, Fe32::V, Fe32::F],
+                &[Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::Q, Fe32::P],
+            );
+            let res = write!(sink(), "{}", im);
+            black_box(&im);
+            black_box(&res);
+        })
+    }
+}