Move ascii::escape_default to libcore
As requested in #46409, the `ascii::escape_default` method has been added to the core library. All I did was copy over the `std::ascii` module file, remove the (redundant) `AsciiExt` trait, and change some of the documentation to match. None of the tests were changed.
I wasn't sure how to handle the annotations. For `EscapeDefault` and `escape_default()`, I changed them to `#[unstable(feature = "core_ascii", issue = "46409")]`. Is that alright? Or should I leave them as they were?
Required moving all fulldeps tests depending on `rand` to different locations as
now there's multiple `rand` crates that can't be implicitly linked against.
Add functions for reversing the bit pattern in an integer
I'm reviving PR #32798 now that the LLVM issues have been resolved.
> This adds the bitreverse intrinsic and adds a reverse_bits function to all integer types.
Make ".e0" not parse as 0.0
This forces floats to have either a digit before the separating point, or after. Thus `".e0"` is invalid like `"."`, when using `parse()`. Fixes#40654. As mentioned in the issue, this is technically a breaking change... but clearly incorrect behaviour at present.
Add std/core::iter::repeat_with
Adds an iterator primitive `repeat_with` which is the "lazy" version of `repeat` but also more flexible since you can build up state with the `FnMut`. The design is mostly taken from `repeat`.
r? @rust-lang/libs
cc @withoutboats, @scottmcm
Add Range[Inclusive]::is_empty
During https://github.com/rust-lang/rfcs/pull/1980, it was discussed that figuring out whether a range is empty was subtle, and thus there should be a clear and obvious way to do it. It can't just be ExactSizeIterator::is_empty (also unstable) because not all ranges are ExactSize -- such as `Range<i64>` and `RangeInclusive<usize>`.
Things to ponder:
- Unless this is stabilized first, this makes stabilizing ExactSizeIterator::is_empty more icky, since this hides that.
- This is only on `Range` and `RangeInclusive`, as those are the only ones where it's interesting. But one could argue that it should be on more for consistency, or on RangeArgument instead.
- The bound on this is PartialOrd, since that works ok (see tests for float examples) and is consistent with `contains`. But ranges like `NAN..=NAN`_are_ kinda weird.
- [x] ~~There's not a real issue number on this yet~~
During the RFC, it was discussed that figuring out whether a range is empty was subtle, and thus there should be a clear and obvious way to do it. It can't just be ExactSizeIterator::is_empty (also unstable) because not all ranges are ExactSize -- not even Range<i32> or RangeInclusive<usize>.
`match`ing on an `Option<Ordering>` seems cause some confusion for LLVM; switching to just using comparison operators removes a few jumps from the simple `for` loops I was trying.
Implement TrustedLen for Take<Repeat> and Take<RangeFrom>
This will allow optimization of simple `repeat(x).take(n).collect()` iterators, which are currently not vectorized and have capacity checks.
This will only support a few aggregates on `Repeat` and `RangeFrom`, which might be enough for simple cases, but doesn't optimize more complex ones. Namely, Cycle, StepBy, Filter, FilterMap, Peekable, SkipWhile, Skip, FlatMap, Fuse and Inspect are not marked `TrustedLen` when the inner iterator is infinite.
Previous discussion can be found in #47082
r? @alexcrichton
Because the last item needs special handling, it seems that LLVM has trouble canonicalizing the loops in external iteration. With the override, it becomes obvious that the start==end case exits the loop (as opposed to the one *after* that exiting the loop in external iteration).
Add slice::ExactChunks and ::ExactChunksMut iterators
These guarantee that always the requested slice size will be returned
and any leftoever elements at the end will be ignored. It allows llvm to
get rid of bounds checks in the code using the iterator.
This is inspired by the same iterators provided by ndarray.
Fixes https://github.com/rust-lang/rust/issues/47115
I'll add unit tests for all this if the general idea and behaviour makes sense for everybody.
Also see https://github.com/rust-lang/rust/issues/47115#issuecomment-354715511 for an example what this improves.
Add iterator method specialisations to Range*
Add specialised implementations of `max` for `Range`, and `last`, `min` and `max` for `RangeInclusive`, all of which lead to significant advantages in the generated assembly on x86.
Note that adding specialisations of `min` and `last` for `Range` led to no benefit, and adding `sum` for `Range` and `RangeInclusive` led to type inference issues (though this is possibly still worthwhile considering the performance gain).
This addresses some of the concerns in #39975.
