Test failures on Debian i386

Start with tests/iterators.rs, especially iter_quantiles_saturated_count_before_max_value and iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket at the reported lines. Reproduce both failures on Debian i386 and investigate the capacity overflow; done means the tests pass there while the existing test suite remains passing.

I recently updated the hdrhistogram package in Debian, and as part of that I resolved the issues that were blocking the tests from running on Debian's test infrastructure.

Unfortunately when running the CI tests on i386 two tests failed, I can also reproduce this locally.

failures:

---- iter_quantiles_saturated_count_before_max_value stdout ----
thread 'iter_quantiles_saturated_count_before_max_value' panicked at 'capacity overflow', library/alloc/src/raw_vec.rs:518:5
stack backtrace:
   0: rust_begin_unwind
             at /usr/src/rustc-1.59.0/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /usr/src/rustc-1.59.0/library/core/src/panicking.rs:116:14
   2: core::panicking::panic
             at /usr/src/rustc-1.59.0/library/core/src/panicking.rs:48:5
   3: alloc::raw_vec::capacity_overflow
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:518:5
   4: alloc::raw_vec::handle_reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:489:34
   5: alloc::raw_vec::RawVec<T,A>::reserve::do_reserve_and_handle
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:287:13
   6: alloc::raw_vec::RawVec<T,A>::reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:291:13
   7: alloc::vec::Vec<T,A>::reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:809:9
   8: alloc::vec::Vec<T,A>::extend_desugared
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:2642:17
   9: <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_extend.rs:18:9
  10: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_from_iter_nested.rs:37:9
  11: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_from_iter.rs:33:9
  12: <alloc::vec::Vec<T> as core::iter::traits::collect::FromIterator<T>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:2541:9
  13: core::iter::traits::iterator::Iterator::collect
             at /usr/src/rustc-1.59.0/library/core/src/iter/traits/iterator.rs:1745:9
  14: iterators::iter_quantiles_saturated_count_before_max_value
             at ./tests/iterators.rs:569:55
  15: iterators::iter_quantiles_saturated_count_before_max_value::{{closure}}
             at ./tests/iterators.rs:561:1
  16: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.59.0/library/core/src/ops/function.rs:227:5
  17: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.59.0/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

---- iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket stdout ----
thread 'iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket' panicked at 'capacity overflow', library/alloc/src/raw_vec.rs:518:5
stack backtrace:
   0: rust_begin_unwind
             at /usr/src/rustc-1.59.0/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /usr/src/rustc-1.59.0/library/core/src/panicking.rs:116:14
   2: core::panicking::panic
             at /usr/src/rustc-1.59.0/library/core/src/panicking.rs:48:5
   3: alloc::raw_vec::capacity_overflow
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:518:5
   4: alloc::raw_vec::handle_reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:489:34
   5: alloc::raw_vec::RawVec<T,A>::reserve::do_reserve_and_handle
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:287:13
   6: alloc::raw_vec::RawVec<T,A>::reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/raw_vec.rs:291:13
   7: alloc::vec::Vec<T,A>::reserve
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:809:9
   8: alloc::vec::Vec<T,A>::extend_desugared
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:2642:17
   9: <alloc::vec::Vec<T,A> as alloc::vec::spec_extend::SpecExtend<T,I>>::spec_extend
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_extend.rs:18:9
  10: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_from_iter_nested.rs:37:9
  11: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/spec_from_iter.rs:33:9
  12: <alloc::vec::Vec<T> as core::iter::traits::collect::FromIterator<T>>::from_iter
             at /usr/src/rustc-1.59.0/library/alloc/src/vec/mod.rs:2541:9
  13: core::iter::traits::iterator::Iterator::collect
             at /usr/src/rustc-1.59.0/library/core/src/iter/traits/iterator.rs:1745:9
  14: iterators::iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket
             at ./tests/iterators.rs:717:55
  15: iterators::iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket::{{closure}}
             at ./tests/iterators.rs:703:1
  16: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.59.0/library/core/src/ops/function.rs:227:5
  17: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.59.0/library/core/src/ops/function.rs:227:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    iter_quantiles_iterates_to_quantile_10_as_it_reaches_last_bucket
    iter_quantiles_saturated_count_before_max_value

test result: FAILED. 18 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 39.15s

Debian i386 uses the x87 FPU and I strongly suspect it's quirky floating point is involved in these failures, but I have no idea how to debug this further.