| Age | Commit message (Collapse) | Author | Lines |
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The check of the `exp` parameter seems useless if we execute the while-loop more than once.
The original implementation of `pow` function using one more comparison if the `exp==0` and may break the pipeline of the cpu, which may generate a slower code.
The performance gap between the old and the new implementation may be small, but IMO, at least the newer one looks more beautiful.
---
bench prog:
```
extern crate test;
($a:expr)=>{let time=std::time::Instant::now();{$a;}print!("{:?} ",time.elapsed())};
($a:expr,$b:literal)=>{let time=std::time::Instant::now();let mut a=0;for _ in 0..$b{a^=$a;}print!("{:?} {} ",time.elapsed(),a)}
}
pub fn pow_rust(x:i64, mut exp: u32) -> i64 {
let mut base = x;
let mut acc = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc * base;
}
exp /= 2;
base = base * base;
}
if exp == 1 {
acc = acc * base;
}
acc
}
pub fn pow_new(x:i64, mut exp: u32) -> i64 {
if exp==0{
1
}else{
let mut base = x;
let mut acc = 1;
while exp > 1 {
if (exp & 1) == 1 {
acc = acc * base;
}
exp >>= 1;
base = base * base;
}
acc * base
}
}
fn main(){
let a=2i64;
let b=1_u32;
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
timing!(test::black_box(a).pow(test::black_box(b)),100000000);
timing!(pow_new(test::black_box(a),test::black_box(b)),100000000);
timing!(pow_rust(test::black_box(a),test::black_box(b)),100000000);
println!();
}
```
bench in my laptop:
```
neutron@Neutron:/me/rust$ rc commit.rs
rustc commit.rs && ./commit
3.978419716s 0 4.079765171s 0 3.964630622s 0
3.997127013s 0 4.260304804s 0 3.997638211s 0
3.963195544s 0 4.11657718s 0 4.176054164s 0
3.830128579s 0 3.980396122s 0 3.937258567s 0
3.986055948s 0 4.127804162s 0 4.018943411s 0
4.185568857s 0 4.217512517s 0 3.98313603s 0
3.863018225s 0 4.030447988s 0 3.694878237s 0
4.206987927s 0 4.137608047s 0 4.115564664s 0
neutron@Neutron:/me/rust$ rc commit.rs -O
rustc commit.rs -O && ./commit
162.111993ms 0 165.107125ms 0 166.26924ms 0
175.20479ms 0 205.062565ms 0 176.278791ms 0
174.408975ms 0 166.526899ms 0 201.857604ms 0
146.190062ms 0 168.592821ms 0 154.61411ms 0
199.678912ms 0 168.411598ms 0 162.129996ms 0
147.420765ms 0 209.759326ms 0 154.807907ms 0
165.507134ms 0 188.476239ms 0 157.351524ms 0
121.320123ms 0 126.401229ms 0 114.86428ms 0
```
delete an unnecessary semicolon...
Sorry for the typo.
delete trailing whitespace
Sorry, too..
Sorry for the missing...
I checked all the implementations, and finally found that there is one function that does not check whether `exp == 0`
add extra tests
add extra tests.
finished adding the extra tests to prevent further typo
add pow(2) to negative exp
add whitespace.
add whitespace
add whitespace
delete extra line
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libstd miri tests: avoid warnings
Ignore tests in a way that all the code still gets compiled, to get rid of all the "unused" warnings that otherwise show up when running the test suite in Miri.
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These three lines are from c82da7a54b9efb1a0ccbe11de66c71f547bf7db9 in
2015.
They cause problems when applying rustfmt to the codebase, because
reordering wildcard imports can trigger new unused import warnings.
As a minimized example, the following program compiles successfully:
#![deny(unused_imports)]
use std::fmt::Debug;
use std::marker::Send;
pub mod repro {
use std::prelude::v1::*;
use super::*;
pub type D = dyn Debug;
pub type S = dyn Send;
}
pub type S = dyn Send;
but putting it through rustfmt produces a program that fails to compile:
#![deny(unused_imports)]
use std::fmt::Debug;
use std::marker::Send;
pub mod repro {
use super::*;
use std::prelude::v1::*;
pub type D = dyn Debug;
pub type S = dyn Send;
}
pub type S = dyn Send;
The error is:
error: unused import: `std::prelude::v1::*`
--> src/main.rs:8:9
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8 | use std::prelude::v1::*;
| ^^^^^^^^^^^^^^^^^^^
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Implement saturating_abs() and saturating_neg() functions for signed integer types
Similar to wrapping_abs() / wrapping_neg() functions but saturating at the numeric bounds instead of wrapping around. Complements the existing set of functions with saturation mechanics.
cc #59983
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Improved test output
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logic is written up in https://github.com/rust-lang/rust/issues/49048
Also, update the documentation slightly
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Ever since we added a Cargo-based build system for the compiler the
standard library has always been a little special, it's never been able
to depend on crates.io crates for runtime dependencies. This has been a
result of various limitations, namely that Cargo doesn't understand that
crates from crates.io depend on libcore, so Cargo tries to build crates
before libcore is finished.
I had an idea this afternoon, however, which lifts the strategy
from #52919 to directly depend on crates.io crates from the standard
library. After all is said and done this removes a whopping three
submodules that we need to manage!
The basic idea here is that for any crate `std` depends on it adds an
*optional* dependency on an empty crate on crates.io, in this case named
`rustc-std-workspace-core`. This crate is overridden via `[patch]` in
this repository to point to a local crate we write, and *that* has a
`path` dependency on libcore.
Note that all `no_std` crates also depend on `compiler_builtins`, but if
we're not using submodules we can publish `compiler_builtins` to
crates.io and all crates can depend on it anyway! The basic strategy
then looks like:
* The standard library (or some transitive dep) decides to depend on a
crate `foo`.
* The standard library adds
```toml
[dependencies]
foo = { version = "0.1", features = ['rustc-dep-of-std'] }
```
* The crate `foo` has an optional dependency on `rustc-std-workspace-core`
* The crate `foo` has an optional dependency on `compiler_builtins`
* The crate `foo` has a feature `rustc-dep-of-std` which activates these
crates and any other necessary infrastructure in the crate.
A sample commit for `dlmalloc` [turns out to be quite simple][commit].
After that all `no_std` crates should largely build "as is" and still be
publishable on crates.io! Notably they should be able to continue to use
stable Rust if necessary, since the `rename-dependency` feature of Cargo
is soon stabilizing.
As a proof of concept, this commit removes the `dlmalloc`,
`libcompiler_builtins`, and `libc` submodules from this repository. Long
thorns in our side these are now gone for good and we can directly
depend on crates.io! It's hoped that in the long term we can bring in
other crates as necessary, but for now this is largely intended to
simply make it easier to manage these crates and remove submodules.
This should be a transparent non-breaking change for all users, but one
possible stickler is that this almost for sure breaks out-of-tree
`std`-building tools like `xargo` and `cargo-xbuild`. I think it should
be relatively easy to get them working, however, as all that's needed is
an entry in the `[patch]` section used to build the standard library.
Hopefully we can work with these tools to solve this problem!
[commit]: https://github.com/alexcrichton/dlmalloc-rs/commit/28ee12db813a3b650a7c25d1c36d2c17dcb88ae3
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This commit changes the test code to compare against easier-to-read, static values instead of relying on the result of `wrapping_add()` which may or may not result in the value that we expect.
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Implement always-fallible TryFrom for usize/isize conversions that are infallible on some platforms
This reverts commit 837d6c70233715a0ae8e15c703d40e3046a2f36a "Remove TryFrom impls that might become conditionally-infallible with a portability lint".
This fixes #49415 by adding (restoring) missing `TryFrom` impls for integer conversions to or from `usize` or `isize`, by making them always fallible at the type system level (that is, with `Error=TryFromIntError`) even though they happen to be infallible on some platforms (for some values of `size_of::<usize>()`).
They had been removed to allow the possibility to conditionally having some of them be infallible `From` impls instead, depending on the platforms, and have the [portability lint](https://github.com/rust-lang/rfcs/pull/1868) warn when they are used in code that is not already opting into non-portability. For example `#[allow(some_lint)] usize::from(x: u64)` would be valid on code that only targets 64-bit platforms.
This PR gives up on this possiblity for two reasons:
* Based on discussion with @aturon, it seems that the portability lint is not happening any time soon. It’s better to have the conversions be available *at all* than keep blocking them for so long. Portability-lint-gated platform-specific APIs can always be added separately later.
* For code that is fine with fallibility, the alternative would force it to opt into "non-portability" even though there would be no real portability issue.
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a portability lint"
This reverts commit 837d6c70233715a0ae8e15c703d40e3046a2f36a.
Fixes https://github.com/rust-lang/rust/issues/49415
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Following up to #49896 and #50629. Fixes #32110.
E0689 is weird.
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Remove some transmutes
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portability lint
https://github.com/rust-lang/rust/pull/49305#issuecomment-376293243
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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.
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This forces floats to have either a digit before the separating point, or after. Thus ".e0" is invalid like ".", when using `parse()`.
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