Crockford32 decoding produces a value that encodes differently

[bradlarsen]

Description

The blockstack_lib::address::c32::c32_address_decode function sometimes successfully decodes its input into a (version, decoded) tuple that is encoded into something different by blockstack_lib::address::c32::c32_address.

It seems like these two functions should be inverses, but this is not the case.

Example

I added the following test case to my copy of src/address/c32.rs:

#[test]
fn test_roundtrip() {
    let s1 = "d9AK57BKNW";
    let (decoded_version, decoded_bytes) = c32_address_decode(s1).unwrap();
    let s2 = c32_address(decoded_version, &decoded_bytes).unwrap();
    assert_eq!(s1, s2);
}

Then, running that test case:

$ cargo test test_roundtrip
   Compiling blockstack-core v0.0.1 (/home/blarsen/audit-blockstack-core)
    Finished test [unoptimized + debuginfo] target(s) in 16.21s
     Running target/debug/deps/blockstack_lib-a4f91b892dca4f5f

running 1 test
test address::c32::test::test_roundtrip ... FAILED

failures:

---- address::c32::test::test_roundtrip stdout ----
thread 'address::c32::test::test_roundtrip' panicked at 'assertion failed: `(left == right)`
  left: `"d9AK57BKNW"`,
 right: `"S9AK57BKNW"`', src/address/c32.rs:404:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

failures:
    address::c32::test::test_roundtrip

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 933 filtered out

error: test failed, to rerun pass '--lib'