This is necessary for decimal-to-float code (in a later commit) to handle
inputs such as 4.9406564584124654e-324 (the smallest subnormal f64).
According to the benchmarks for flt2dec::dragon, this does not
affect performance measurably. It probably uses slightly more stack
space though.
Improve siphash performance for longer data
Use `ptr::copy_nonoverlapping` (aka memcpy) to load an u64 from the
byte stream. This is correct for any alignment, and the compiler will
use the appropriate instruction to load the data.
Also contains small tweaks that should benefit hashing short data too,
both the commit that removes a variable and the autovectorization of
the hash state initialization (in SipHash::reset).
Benchmarks show that hashing longer data benefits for the improved word loading.
Before (using benchmarks from the first commit in the PR):
The before benchmark is a bit noisy.
```
test hash::sip::bench_bytes_4 ... bench: 41 ns/iter (+/- 0) = 97 MB/s
test hash::sip::bench_bytes_7 ... bench: 49 ns/iter (+/- 2) = 142 MB/s
test hash::sip::bench_bytes_8 ... bench: 42 ns/iter (+/- 4) = 190 MB/s
test hash::sip::bench_bytes_a_16 ... bench: 57 ns/iter (+/- 14) = 280 MB/s
test hash::sip::bench_bytes_b_32 ... bench: 85 ns/iter (+/- 74) = 376 MB/s
test hash::sip::bench_bytes_c_128 ... bench: 278 ns/iter (+/- 33) = 460 MB/s
test hash::sip::bench_long_str ... bench: 825 ns/iter (+/- 103)
test hash::sip::bench_str_of_8_bytes ... bench: 151 ns/iter (+/- 66)
test hash::sip::bench_str_over_8_bytes ... bench: 59 ns/iter (+/- 3)
test hash::sip::bench_str_under_8_bytes ... bench: 47 ns/iter (+/- 56)
test hash::sip::bench_u32 ... bench: 39 ns/iter (+/- 93) = 205 MB/s
test hash::sip::bench_u32_keyed ... bench: 40 ns/iter (+/- 88) = 200 MB/s
test hash::sip::bench_u64 ... bench: 54 ns/iter (+/- 96) = 148 MB/s
```
After:
```
test hash::sip::bench_bytes_4 ... bench: 41 ns/iter (+/- 3) = 97 MB/s
test hash::sip::bench_bytes_7 ... bench: 48 ns/iter (+/- 0) = 145 MB/s
test hash::sip::bench_bytes_8 ... bench: 35 ns/iter (+/- 1) = 228 MB/s
test hash::sip::bench_bytes_a_16 ... bench: 45 ns/iter (+/- 1) = 355 MB/s
test hash::sip::bench_bytes_b_32 ... bench: 60 ns/iter (+/- 0) = 533 MB/s
test hash::sip::bench_bytes_c_128 ... bench: 161 ns/iter (+/- 5) = 795 MB/s
test hash::sip::bench_long_str ... bench: 514 ns/iter (+/- 5)
test hash::sip::bench_str_of_8_bytes ... bench: 44 ns/iter (+/- 0)
test hash::sip::bench_str_over_8_bytes ... bench: 51 ns/iter (+/- 0)
test hash::sip::bench_str_under_8_bytes ... bench: 52 ns/iter (+/- 6)
test hash::sip::bench_u32 ... bench: 40 ns/iter (+/- 2) = 200 MB/s
test hash::sip::bench_u32_keyed ... bench: 39 ns/iter (+/- 1) = 205 MB/s
test hash::sip::bench_u64 ... bench: 36 ns/iter (+/- 1) = 222 MB/s
```
The common pattern `iter::repeat(elt).take(n).collect::<Vec<_>>()` is
exactly equivalent to `vec![elt; n]`, do this replacement in the whole
tree.
(Actually, vec![] is smart enough to only call clone n - 1 times, while
the former solution would call clone n times, and this fact is
virtually irrelevant in practice.)
I added it because it was easy (same a `char::to_lowercase`,
just a different table), but it doesn’t make sense to have this
in std but not str::to_titlecase, which would require
https://github.com/unicode-rs/unicode-segmentation
At some point in the future this feature will be available
(both on char and str) in a crates.io crate.
As it says in the title. I've added an `expect` method to `Result` that allows printing both an error message (e.g. what operation was attempted), and the error value. This is separate from the `unwrap` and `ok().expect("message")` behaviours.
This is a direct port of my prior work on the float formatting. The detailed description is available [here](https://github.com/lifthrasiir/rust-strconv#flt2dec). In brief,
* This adds a new hidden module `core::num::flt2dec` for testing from `libcoretest`. Why is it in `core::num` instead of `core::fmt`? Because I envision that the table used by `flt2dec` is directly applicable to `dec2flt` (cf. #24557) as well, which exceeds the realm of "formatting".
* This contains both Dragon4 algorithm (exact, complete but slow) and Grisu3 algorithm (exact, fast but incomplete).
* The code is accompanied with a large amount of self-tests and some exhaustive tests. In particular, `libcoretest` gets a new dependency on `librand`. For the external interface it relies on the existing test suite.
* It is known that, in the best case, the entire formatting code has about 30 KBs of binary overhead (judged from strconv experiments). Not too bad but there might be a potential room for improvements.
This is rather large code. I did my best to comment and annotate the code, but you have been warned.
For the maximal availability the original code was licensed in CC0, but I've also dual-licensed it in MIT/Apache as well so there should be no licensing concern.
This is [breaking-change] as it changes the float output slightly (and it also affects the casing of `inf` and `nan`). I hope this is not a big deal though :)
Fixes#7030, #18038 and #24556. Also related to #6220 and #20870.
## Known Issues
- [x] I've yet to finish `make check-stage1`. It does pass main test suites including `run-pass` but there might be some unknown edges on the doctests.
- [ ] Figure out how this PR affects rustc.
- [ ] Determine which internal routine is mapped to the formatting specifier. Depending on the decision, some internal routine can be safely removed (for instance, currently `to_shortest_str` is unused).
For the shortest mode the IEEE 754 decoder already provides
an exact rounding range accounting for banker's rounding,
but it was not the case for the exact mode. This commit alters
the exact mode algorithm for Dragon so that any number ending at
`...x5000...` with even `x` and infinite zeroes will round to
`...x` instead of `...(x+1)` as it was. Grisu is not affected
by this change because this halfway case always results in
the failure for Grisu.
The bug involves the incorrect logic for `core::num::flt2dec::decoder`.
This makes some numbers in the form of 2^n missing one final digits,
which breaks the bijectivity criterion. The regression tests have been
added, and f32 exhaustive test is rerun to get the updated result.
This is a fork of the flt2dec portion of rust-strconv [1] with
a necessary relicensing (the original code was licensed CC0-1.0).
Each module is accompanied with large unit tests, integrated
in this commit as coretest::num::flt2dec. This module is added
in order to replace the existing core::fmt::float method.
The forked revision of rust-strconv is from 2015-04-20, with a commit ID
9adf6d3571c6764a6f240a740c823024f70dc1c7.
[1] https://github.com/lifthrasiir/rust-strconv/
Specifically, make count, nth, and last call the corresponding methods
on the underlying iterator where possible. This way, if the underlying
iterator has an optimized count, nth, or last implementations (e.g.
slice::Iter), these methods will propagate these optimizations.
Additionally, change Skip::next to take advantage of a potentially
optimized nth method on the underlying iterator.
These implementations were intended to be unstable, but currently the stability
attributes cannot handle a stable trait with an unstable `impl` block. This
commit also audits the rest of the standard library for explicitly-`#[unstable]`
impl blocks. No others were removed but some annotations were changed to
`#[stable]` as they're defacto stable anyway.
One particularly interesting `impl` marked `#[stable]` as part of this commit
is the `Add<&[T]>` impl for `Vec<T>`, which uses `push_all` and implicitly
clones all elements of the vector provided.
Closes#24791
[breaking-change]
These implementations were intended to be unstable, but currently the stability
attributes cannot handle a stable trait with an unstable `impl` block. This
commit also audits the rest of the standard library for explicitly-`#[unstable]`
impl blocks. No others were removed but some annotations were changed to
`#[stable]` as they're defacto stable anyway.
One particularly interesting `impl` marked `#[stable]` as part of this commit
is the `Add<&[T]>` impl for `Vec<T>`, which uses `push_all` and implicitly
clones all elements of the vector provided.
Closes#24791
core: Fix size_hint for signed integer `Range<T>` iterators
There was an overflow bug in .size_hint() for signed iterators, which
produced an hilariously incorrect size or an overflow panic.
Incorrect size is a serious bug since the iterators are marked
ExactSizeIterator. (And leads to abort() on (-1i8..127).collect() when
the collection tries to preallocate too much).
> (-1i8..127).size_hint()
(18446744073709551488, Some(18446744073709551488))
Bug found using quickcheck.
Fixes#24851
Instead of using the O(n) defaults, define O(1) shortcuts. I also copied (and slightly modified) the relevant tests from the iter tests into the slice tests just in case someone comes along and changes them in the future.
Partially implements #24214.
There was an overflow bug in .size_hint() for signed iterators, which
produced an hilariously incorrect size or an overflow panic.
Incorrect size is a serious bug since the iterators are marked
ExactSizeIterator. (And leads to abort() on (-1i8..127).collect() when
the collection tries to preallocate too much).
All signed range iterators were affected.
> (-1i8..127).size_hint()
(18446744073709551488, Some(18446744073709551488))
Bug found using quickcheck.
Fixes#24851
Changes the style guidelines regarding unit tests to recommend using a
sub-module named "tests" instead of "test" for unit tests as "test"
might clash with imports of libtest.
