The "nth" element can be confusing. In an array context, we know indexes
start from 0 but one may believe this is not the case with "nth". For
example, would `.nth(1)` return the first (1th/1st) or the second
element? Rephrase a bit to be less confusing.
r? @steveklabnik
The replacements are functions that usually use a single `mem::transmute` in
their body and restrict input and output via more concrete types than `T` and
`U`. Worth noting are the `transmute` functions for slices and the `from_utf8*`
family for mutable slices. Additionally, `mem::transmute` was often used for
casting raw pointers, when you can already cast raw pointers just fine with
`as`.
The "nth" element can be confusing. In an array context, we know indexes
start from 0 but one may believe this is not the case with "nth". For
example, would `.nth(1)` return the first (1th/1st) or the second
element? Rephrase a bit to be less confusing.
We were burying the reason to use this function below a bunch of caveats about
its usage. That's backwards. Why a function should be used belongs at the top of
the docs, not the bottom.
Also, add some extra links to related functions mentioned in the body.
/cc @abhijeetbhagat who pointed this out on IRC
This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.
[rfc]: https://github.com/rust-lang/rfcs/pull/1184Closes#27394
We were burying the reason to use this function below a bunch of caveats about
its usage. That's backwards. Why a function should be used belongs at the top of
the docs, not the bottom.
Also, add some extra links to related functions mentioned in the body.
This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.
[rfc]: https://github.com/rust-lang/rfcs/pull/1184
There are still problems in both the design and implementation of this, so we don't want it landing in 1.2.
cc @arielb1 @nikomatsakis
cc #27364
r? @alexcrichton
The following APIs were all marked with a `#[stable]` tag:
* process::Child::id
* error::Error::is
* error::Error::downcast
* error::Error::downcast_ref
* error::Error::downcast_mut
* io::Error::get_ref
* io::Error::get_mut
* io::Error::into_inner
* hash::Hash::hash_slice
* hash::Hasher::write_{i,u}{8,16,32,64,size}
This isn't actually necessary any more with the advent of `$crate` and changes
in the compiler to expand macros to `::core::$foo` in the context of a
`#![no_std]` crate.
The libcore inner module was also trimmed down a bit to the bare bones.
I think this was just missed when `Send` and `Sync` were redone, since it seems odd to not be able to use things like `Arc<AtomicPtr>`. If it was intentional feel free to just close this.
I used another test as a template for writing mine, so I hope I got all the headers and stuff right.
This isn't actually necessary any more with the advent of `$crate` and changes
in the compiler to expand macros to `::core::$foo` in the context of a
`#![no_std]` crate.
The libcore inner module was also trimmed down a bit to the bare bones.
As described in the module documentation, the memory orderings in Rust
are the same with that of LLVM. However, the documentation for the
memory orderings enum says the memory orderings are the same of that of
C++. Note that they differ in that C++'s support the consume reads,
while LLVM's does not. Hence this commit fixes the bug in the
documentation for the enum.
As described in the module documentation, the memory orderings in Rust
are the same with that of LLVM. However, the documentation for the
memory orderings enum says the memory orderings are the same of that of
C++. Note that they differ in that C++'s support the consume reads,
while LLVM's does not. Hence this commit fixes the bug in the
documentation for the enum.
The following APIs were all marked with a `#[stable]` tag:
* process::Child::id
* error::Error::is
* error::Error::downcast
* error::Error::downcast_ref
* error::Error::downcast_mut
* io::Error::get_ref
* io::Error::get_mut
* io::Error::into_inner
* hash::Hash::hash_slice
* hash::Hasher::write_{i,u}{8,16,32,64,size}
I had to modify some tests : since `wtf8buf_show` and `wtf8_show` were doing the exact same thing, I repurposed `wtf8_show` to `wtf8buf_show_str` which ensures `Wtf8Buf` `Debug`-formats the same as `str`.
`write_str_escaped` might also be shared amongst other `fmt` but I just left it there within `Wtf8::fmt` for review.
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
```
Many of these have long since reached their stage of being obsolete, so this
commit starts the removal process for all of them. The unstable features that
were deprecated are:
* box_heap
* cmp_partial
* fs_time
* hash_default
* int_slice
* iter_min_max
* iter_reset_fuse
* iter_to_vec
* map_in_place
* move_from
* owned_ascii_ext
* page_size
* read_and_zero
* scan_state
* slice_chars
* slice_position_elem
* subslice_offset
Many of these have long since reached their stage of being obsolete, so this
commit starts the removal process for all of them. The unstable features that
were deprecated are:
* cmp_partial
* fs_time
* hash_default
* int_slice
* iter_min_max
* iter_reset_fuse
* iter_to_vec
* map_in_place
* move_from
* owned_ascii_ext
* page_size
* read_and_zero
* scan_state
* slice_chars
* slice_position_elem
* subslice_offset
If they are ordered v0, v2, v1, v3, the compiler can find just a few
simd optimizations itself.
The new optimization I could observe on x86-64 was using 128 bit
registers for the v = key ^ constant operations in new / reset.
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.
Use unchecked indexing.
This results in a large improvement of throughput (hashed bytes
/ second) for long data. Maximum improvement benches at a 70% increase
in throughput for large values (> 256 bytes) but already values of 16
bytes or larger improve.
Introducing unchecked indexing is motivated to reach as good throughput
as possible. Using ptr::copy_nonoverlapping without unchecked indexing
would land the improvement some 20-30 pct units lower.
We use a debug assertion so that the test suite checks our use of
unchecked indexing.
Macro desugaring of `in PLACE { BLOCK }` into "simpler" expressions following the in-development "Placer" protocol.
Includes Placer API that one can override to integrate support for `in` into one's own type. (See [RFC 809].)
[RFC 809]: https://github.com/rust-lang/rfcs/blob/master/text/0809-box-and-in-for-stdlib.md
Part of #22181
Replaced PR #26180.
Turns on the `in PLACE { BLOCK }` syntax, while leaving in support for the old `box (PLACE) EXPR` syntax (since we need to support that at least until we have a snapshot with support for `in PLACE { BLOCK }`.
(Note that we are not 100% committed to the `in PLACE { BLOCK }` syntax. In particular I still want to play around with some other alternatives. Still, I want to get the fundamental framework for the protocol landed so we can play with implementing it for non `Box` types.)
----
Also, this PR leaves out support for desugaring-based `box EXPR`. We will hopefully land that in the future, but for the short term there are type-inference issues injected by that change that we want to resolve separately.
