Suspected regression in cc1930a

[Schuwi]

There seems to be some kind of regression in cc1930a. This library is used in https://github.com/feather-rs/feather (server/worldgen/src/density_map/) and from revision cc1930a onwards one of the tests in feather (server/worldgen/src/lib.rs) fails to complete:

assertion failed: y < CHUNK_HEIGHT
thread 'tests::test_reproducability' panicked at 'assertion failed: y < CHUNK_HEIGHT', core/chunk/src/lib.rs:401:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1052
   5: std::io::Write::write_fmt
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/libstd/io/mod.rs:1426
   6: std::io::impls::<impl std::io::Write for alloc::boxed::Box<W>>::write_fmt
             at src/libstd/io/impls.rs:156
   7: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   8: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   9: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:204
  10: std::panicking::default_hook
             at src/libstd/panicking.rs:221
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:472
  12: std::panicking::begin_panic
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/libstd/panicking.rs:399
  13: feather_chunk::Chunk::check_coords
             at core/chunk/src/lib.rs:401
  14: feather_chunk::Chunk::set_block_at
             at core/chunk/src/lib.rs:221
  15: <feather_server_worldgen::finishers::snow::SnowFinisher as feather_server_worldgen::FinishingGenerator>::generate_for_chunk
             at server/worldgen/src/finishers/snow.rs:24
  16: <feather_server_worldgen::ComposableGenerator as feather_server_worldgen::WorldGenerator>::generate_chunk
             at server/worldgen/src/lib.rs:180
  17: feather_server_worldgen::tests::test_reproducability
             at server/worldgen/src/lib.rs:422
  18: feather_server_worldgen::tests::test_reproducability::{{closure}}
             at server/worldgen/src/lib.rs:410
  19: core::ops::function::FnOnce::call_once
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/libcore/ops/function.rs:232
  20: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/liballoc/boxed.rs:1015
  21: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:86
  22: std::panicking::try
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/libstd/panicking.rs:281
  23: std::panic::catch_unwind
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447/src/libstd/panic.rs:394
  24: test::run_test_in_process
             at src/libtest/lib.rs:539
  25: test::run_test::run_test_inner::{{closure}}
             at src/libtest/lib.rs:452
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

I can't really give you more insight into what exactly went wrong here though, as I have no knowledge of this topic whatsoever, it's just something I noticed when incorporating #31 in feather and I wanted to let you know.

[Ralith]

To be clear, it does not occur in b8c864f0b96ad21c259971b757620aacb357fba4? That commit (and its immediate ancestors) changed the output range of everything, and that looks like the sort of failure you'd expect from that. I made an effort to avoid changing the results in #29, but it's possible I missed something.

[Schuwi]

f642fa7 and previous => works 580d123 and following => doesn't work Also noticed a stack overflow in our test when running with opt-level=0 with f642fa7, which wasn't there in 3.1.5 and doesn't occur with opt-level=1. Guess I'll have to investigate that further.

[Ralith]

580d123 and following => doesn't work

Yeah, that's 100% expected then. Noise amplitudes were mapped into a consistent range, so you'll need to update any scaling factors you used. Output should be otherwise unchanged. See discussion in #27 for details.

Also noticed a stack overflow in our test when running with opt-level=0 with f642fa7

Maybe a dupe of #25?

[Schuwi]

Yeah, I don't understand a word of the comments in that PR ^^ I'll open an issue in feather and leave it to someone who knows this stuff to implement the new version. Those changes to amplitude will require a MAJOR version bump though, right?

Maybe a dupe of #25?

Thanks, added a comment.

[jackmott]

definitely going to be a major version bump in the next version

[Schuwi]

Okay, so everything working as intended after all. Thanks for the help!