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Implement useful steps_between for all integers
We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.
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Remove duplicated code from Iterator::{ne, lt, le, gt, ge}
This PR delegates `Iterator::ne` to `Iterator::eq` and `Iterator::{lt, le, gt, ge}` to `Iterator::partial_cmp`.
Oddly enough, this change actually simplifies the generated assembly [in some cases](https://rust.godbolt.org/z/riBtNe), although I don't understand assembly well enough to see if the longer assembly is doing something clever.
I also added two extremely simple benchmarks:
```
// before
test iter::bench_lt ... bench: 98,404 ns/iter (+/- 21,008)
test iter::bench_partial_cmp ... bench: 62,437 ns/iter (+/- 5,009)
// after
test iter::bench_lt ... bench: 61,757 ns/iter (+/- 8,770)
test iter::bench_partial_cmp ... bench: 62,151 ns/iter (+/- 13,753)
```
I have no idea why the current `lt`/`le`/`gt`/`ge` implementations don't seem to be compiled optimally, but simply having them call `partial_cmp` seems to be an improvement.
See #44729 for a previous discussion.
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This was incorrectly copypasta'd from RepeatWith.
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We can use `usize::try_from` to convert steps from any size of integer.
This enables a meaningful `size_hint()` for larger ranges, rather than
always just `(0, None)`. Now they return the true `(len, Some(len))`
when it fits, otherwise `(usize::MAX, None)` for overflow.
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in stdlib docs
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No old chestnuts in iter::repeat docs
The current language may be amusing, yet is just imprecise and most especially difficult to understand for someone who speaks English as a foreign language.
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A few improvements to comments in user-facing crates
Not too many this time, and all concern comments (almost all doc comments) in user-facing crates (libstd, libcore, liballoc).
r? @steveklabnik
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The current language may be amusing, yet is just imprecise and most especially difficult to understand for someone who speaks English as a foreign language.
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RangeInclusive internal iteration performance improvement.
Specialize `Iterator::try_fold` and `DoubleEndedIterator::try_rfold` to improve code generation in all internal iteration scenarios.
This changes brings the performance of internal iteration with `RangeInclusive` on par with the performance of iteration with `Range`:
- Single conditional jump in hot loop,
- Unrolling and vectorization,
- And even Closed Form substitution.
Unfortunately, it only applies to internal iteration. Despite various attempts at stream-lining the implementation of `next` and `next_back`, LLVM has stubbornly refused to optimize external iteration appropriately, leaving me with a choice between:
- The current implementation, for which Closed Form substitution is performed, but which uses 2 conditional jumps in the hot loop when optimization fail.
- An implementation using a `is_done` boolean, which uses 1 conditional jump in the hot loop when optimization fail, allowing unrolling and vectorization, but for which Closed Form substitution fails.
In the absence of any conclusive evidence as to which usecase matters most, and with no assurance that the lack of Closed Form substitution is not indicative of other optimizations being foiled, there is no way
to pick one implementation over the other, and thus I defer to the statu quo as far as `next` and `next_back` are concerned.
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FCP: https://github.com/rust-lang/rust/issues/55977#issuecomment-463964234
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FCP: https://github.com/rust-lang/rust/issues/58045#issuecomment-464674773
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The phrase "... or some similar thing." is very vague and contributes nothing to understanding the example. Simply removed.
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Specialize Iterator::try_fold and DoubleEndedIterator::try_rfold to
improve code generation in all internal iteration scenarios.
This changes brings the performance of internal iteration with
RangeInclusive on par with the performance of iteration with Range:
- Single conditional jump in hot loop,
- Unrolling and vectorization,
- And even Closed Form substitution.
Unfortunately, it only applies to internal iteration. Despite various
attempts at stream-lining the implementation of next and next_back,
LLVM has stubbornly refused to optimize external iteration
appropriately, leaving me with a choice between:
- The current implementation, for which Closed Form substitution is
performed, but which uses 2 conditional jumps in the hot loop when
optimization fail.
- An implementation using a "is_done" boolean, which uses 1
conditional jump in the hot loop when optimization fail, allowing
unrolling and vectorization, but for which Closed Form substitution
fails.
In the absence of any conclusive evidence as to which usecase matters
most, and with no assurance that the lack of Closed Form substitution
is not indicative of other optimizations being foiled, there is no way
to pick one implementation over the other, and thus I defer to the
statu quo as far as next and next_back are concerned.
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Update visibility of intermediate use items.
Fixes #57410 and fixes #53925 and fixes #47816.
Currently, the target of a use statement will be updated with
the visibility of the use statement itself (if the use statement was
visible).
This PR ensures that if the path to the target item is via another
use statement then that intermediate use statement will also have the
visibility updated like the target. This silences incorrect
`unreachable_pub` lints with inactionable suggestions.
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Currently, the target of a use statement will be updated with
the visibility of the use statement itself (if the use statement was
visible).
This commit ensures that if the path to the target item is via another
use statement then that intermediate use statement will also have the
visibility updated like the target. This silences incorrect
`unreachable_pub` lints with inactionable suggestions.
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This API is unstable.
CC https://github.com/rust-lang/rust/issues/55977#issuecomment-459657195
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