This commit removes the previous mechanism of differentiating
between "Debug" and "Display" formattings for the sign of -0 so as
to comply with the IEEE 754 standard's requirements on external
character sequences preserving various attributes of a floating
point representation.
In addition, numerous tests are fixed.
Fix formatting specifiers doc links
d36e3e23a8 seems to have inadvertently changed many of these links to point to `core::fmt` instead of `std::fmt`. The information about formatting specifiers is only documented in [`std::fmt`](https://doc.rust-lang.org/std/fmt/); [`core::fmt`](https://doc.rust-lang.org/core/fmt/) is empty. 3baf6a4a74 seems to have already fixed a couple of these links to point back to `std::fmt`.
Avoid panic_bounds_check in fmt::write.
Writing any fmt::Arguments would trigger the inclusion of usize formatting and padding code in the resulting binary, because indexing used in fmt::write would generate code using panic_bounds_check, which prints the index and length.
These bounds checks are not necessary, as fmt::Arguments never contains any out-of-bounds indexes.
This change replaces them with unsafe get_unchecked, to reduce the amount of generated code, which is especially important for embedded targets.
---
Demonstration of the size of and the symbols in a 'hello world' no_std binary:
<details>
<summary>Source code</summary>
```rust
#![feature(lang_items)]
#![feature(start)]
#![no_std]
use core::fmt;
use core::fmt::Write;
#[link(name = "c")]
extern "C" {
#[allow(improper_ctypes)]
fn write(fd: i32, s: &str) -> isize;
fn exit(code: i32) -> !;
}
struct Stdout;
impl fmt::Write for Stdout {
fn write_str(&mut self, s: &str) -> fmt::Result {
unsafe { write(1, s) };
Ok(())
}
}
#[start]
fn main(_argc: isize, _argv: *const *const u8) -> isize {
let _ = writeln!(Stdout, "Hello World");
0
}
#[lang = "eh_personality"]
fn eh_personality() {}
#[panic_handler]
fn panic(_: &core::panic::PanicInfo) -> ! {
unsafe { exit(1) };
}
```
</details>
Before:
```
text data bss dec hex filename
6059 736 8 6803 1a93 before
```
```
0000000000001e00 T <T as core::any::Any>::type_id
0000000000003dd0 D core::fmt::num::DEC_DIGITS_LUT
0000000000001ce0 T core::fmt::num:👿:<impl core::fmt::Display for u64>::fmt
0000000000001ce0 T core::fmt::num:👿:<impl core::fmt::Display for usize>::fmt
0000000000001370 T core::fmt::write
0000000000001b30 t core::fmt::Formatter::pad_integral::write_prefix
0000000000001660 T core::fmt::Formatter::pad_integral
0000000000001350 T core::ops::function::FnOnce::call_once
0000000000001b80 t core::ptr::drop_in_place
0000000000001120 t core::ptr::drop_in_place
0000000000001c50 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001c90 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001b90 T core::panicking::panic_bounds_check
0000000000001c10 T core::panicking::panic_fmt
0000000000001130 t <&mut W as core::fmt::Write>::write_char
0000000000001200 t <&mut W as core::fmt::Write>::write_fmt
0000000000001250 t <&mut W as core::fmt::Write>::write_str
```
After:
```
text data bss dec hex filename
3068 600 8 3676 e5c after
```
```
0000000000001360 T core::fmt::write
0000000000001340 T core::ops::function::FnOnce::call_once
0000000000001120 t core::ptr::drop_in_place
0000000000001620 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001660 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001130 t <&mut W as core::fmt::Write>::write_char
0000000000001200 t <&mut W as core::fmt::Write>::write_fmt
0000000000001250 t <&mut W as core::fmt::Write>::write_str
```
The lint checks arguments in calls to `transmute` or functions that have
`Pointer` as a trait bound and displays a warning if the argument is a function
reference. Also checks for `std::fmt::Pointer::fmt` to handle formatting macros
although it doesn't depend on the exact expansion of the macro or formatting
internals. `std::fmt::Pointer` and `std::fmt::Pointer::fmt` were also added as
diagnostic items and symbols.
Writing any fmt::Arguments would trigger the inclusion of usize
formatting and padding code in the resulting binary, because indexing
used in fmt::write would generate code using panic_bounds_check, which
prints the index and length.
These bounds checks are not necessary, as fmt::Arguments never contains
any out-of-bounds indexes.
This change replaces them with unsafe get_unchecked, to reduce the
amount of generated code, which is especially important for embedded
targets.
Use less divisions in display u128/i128
This PR is an absolute mess, and I need to test if it improves the speed of fmt::Display for u128/i128, but I think it's correct.
It hopefully is more efficient by cutting u128 into at most 2 u64s, and also chunks by 1e16 instead of just 1e4.
Also I specialized the implementations for uints to always be non-false because it bothered me that it was checked at all
Do not merge until I benchmark it and also clean up the god awful mess of spaghetti.
Based on prior work in #44583
cc: `@Dylan-DPC`
Due to work on `itoa` and suggestion in original issue:
r? `@dtolnay`
Add zero padding
Add benchmarks for fmt u128
This tests both when there is the max amount of work(all characters used)
And least amount of work(1 character used)
rustdoc: do not use plain summary for trait impls
Fixes#38386.
Fixes#48332.
Fixes#49430.
Fixes#62741.
Fixes#73474.
Unfortunately this is not quite ready to go because the newly-working links trigger a bunch of linkcheck failures. The failures are tough to fix because the links are resolved relative to the implementor, which could be anywhere in the module hierarchy.
(In the current docs, these links end up rendering as uninterpreted markdown syntax, so I don't think these failures are any worse than the status quo. It might be acceptable to just add them to the linkchecker whitelist.)
Ideally this could be fixed with intra-doc links ~~but it isn't working for me: I am currently investigating if it's possible to solve it this way.~~ Opened #73829.
EDIT: This is now ready!
