Document powf and powi values that are always 1.0 #136012

hkBst · 2025-01-24T17:03:07Z

fixes bug #90429

rustbot · 2025-01-24T17:03:16Z

rustbot has assigned @ibraheemdev.
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compiler-errors · 2025-01-24T20:08:57Z

Like @matthiaskrgr noted in the other PR, please merge these into one. I'm gonna leave this one open and close the rest.

compiler-errors · 2025-01-24T20:11:14Z

Also regarding this and those other PRs, please squash them into a single commit. A commit named "Add semicolon", "add space", etc is not adding much value to a 1 file change PR -- if you need help learning how to squash commits into one, I think any of us can point you how to do that :)

workingjubilee · 2025-01-24T20:16:20Z

@hkBst While we will not necessarily refuse PRs that have a remunerative motivation, we will definitely not accept degrading the quality of PRs to do so. I will accept this when you push an actual fix and it passes the standard of my review, and no sooner.

hkBst · 2025-01-25T00:31:18Z

@workingjubilee no remunerative motivation I can assure you. Apologies for any confusion arising from my use of the word "payout".

EDIT: I meant "payoff" when I used "payout" (in the other comment), so I guess I was unidiomatic. Again, apologies for the confusion.

workingjubilee · 2025-01-27T22:40:49Z

Thank you.

Yes, idiomatic English can be somewhat challenging, so I understand the slip. I also understand why you think it would be more efficient (or otherwise better) to send 4 PRs. It's just actually worse to have 4 people look at basically the same diff and have to individually activate their neurons to decide if the change is okay.

Most importantly, they might decide differently, which is very bad. This documentation should absolutely be consistent between types (modulo where it needs to deviate, like value ranges).

workingjubilee

Much better, thank you.

workingjubilee · 2025-01-27T22:43:09Z

@bors r+ rollup

bors · 2025-01-27T22:43:11Z

📌 Commit 5297fc1 has been approved by workingjubilee

It is now in the queue for this repository.

hkBst · 2025-01-28T06:58:59Z

@tgross35 Ah, I wondered what those were for, but could not find anywhere that explained them... Now added.

tgross35 · 2025-01-28T07:17:19Z

library/std/src/f128.rs

+    /// ```
+    /// #![feature(f128)]
+    /// # #[cfg(reliable_f128_math)] {
+    ///
+    /// let x = 2.0_f128;
+    /// let abs_difference = (x.powi(2) - (x * x)).abs();
+    /// assert!(abs_difference <= f128::EPSILON);
+    ///
+    /// assert_eq!(f128::powi(f128::NAN, 0), 1.0);
+    /// ```


These need the trailing # } to match the opening # #[cfg(...)] {

Right, of course... done now.

hkBst · 2025-01-28T07:36:34Z

@rustbot ready

tgross35

Thanks for the changes, LGTM but I'll wait for PR CI to pass.

@tgross35 Ah, I wondered what those were for, but could not find anywhere that explained them... Now added.

For reference, these get set here and the reasons are reasonably well documented

rust/library/std/build.rs

Lines 82 to 186 in 2f348cb

    
           // Emit these on platforms that have no known ABI bugs, LLVM selection bugs, lowering bugs, 
        
           // missing symbols, or other problems, to determine when tests get run. 
        
           // If more broken platforms are found, please update the tracking issue at 
        
           // <https://github.com/rust-lang/rust/issues/116909> 
        
           // 
        
           // Some of these match arms are redundant; the goal is to separate reasons that the type is 
        
           // unreliable, even when multiple reasons might fail the same platform. 
        
           println!("cargo:rustc-check-cfg=cfg(reliable_f16)"); 
        
           println!("cargo:rustc-check-cfg=cfg(reliable_f128)"); 
        
           // This is a step beyond only having the types and basic functions available. Math functions 
        
           // aren't consistently available or correct. 
        
           println!("cargo:rustc-check-cfg=cfg(reliable_f16_math)"); 
        
           println!("cargo:rustc-check-cfg=cfg(reliable_f128_math)"); 
        
           let has_reliable_f16 = match (target_arch.as_str(), target_os.as_str()) { 
        
               // We can always enable these in Miri as that is not affected by codegen bugs. 
        
               _ if is_miri => true, 
        
               // Selection failure <https://github.com/llvm/llvm-project/issues/50374> 
        
               ("s390x", _) => false, 
        
               // Unsupported <https://github.com/llvm/llvm-project/issues/94434> 
        
               ("arm64ec", _) => false, 
        
               // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054> 
        
               ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false, 
        
               // Infinite recursion <https://github.com/llvm/llvm-project/issues/97981> 
        
               ("csky", _) => false, 
        
               ("hexagon", _) => false, 
        
               ("loongarch64", _) => false, 
        
               ("mips" | "mips64" | "mips32r6" | "mips64r6", _) => false, 
        
               ("powerpc" | "powerpc64", _) => false, 
        
               ("sparc" | "sparc64", _) => false, 
        
               ("wasm32" | "wasm64", _) => false, 
        
               // `f16` support only requires that symbols converting to and from `f32` are available. We 
        
               // provide these in `compiler-builtins`, so `f16` should be available on all platforms that 
        
               // do not have other ABI issues or LLVM crashes. 
        
               _ => true, 
        
           }; 
        
           let has_reliable_f128 = match (target_arch.as_str(), target_os.as_str()) { 
        
               // We can always enable these in Miri as that is not affected by codegen bugs. 
        
               _ if is_miri => true, 
        
               // Unsupported <https://github.com/llvm/llvm-project/issues/94434> 
        
               ("arm64ec", _) => false, 
        
               // Selection bug <https://github.com/llvm/llvm-project/issues/96432> 
        
               ("mips64" | "mips64r6", _) => false, 
        
               // Selection bug <https://github.com/llvm/llvm-project/issues/95471> 
        
               ("nvptx64", _) => false, 
        
               // ABI bugs <https://github.com/rust-lang/rust/issues/125109> et al. (full 
        
               // list at <https://github.com/rust-lang/rust/issues/116909>) 
        
               ("powerpc" | "powerpc64", _) => false, 
        
               // ABI unsupported  <https://github.com/llvm/llvm-project/issues/41838> 
        
               ("sparc", _) => false, 
        
               // Stack alignment bug <https://github.com/llvm/llvm-project/issues/77401>. NB: tests may 
        
               // not fail if our compiler-builtins is linked. 
        
               ("x86", _) => false, 
        
               // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054> 
        
               ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false, 
        
               // There are no known problems on other platforms, so the only requirement is that symbols 
        
               // are available. `compiler-builtins` provides all symbols required for core `f128` 
        
               // support, so this should work for everything else. 
        
               _ => true, 
        
           }; 
        
           // Configure platforms that have reliable basics but may have unreliable math. 
        
           // LLVM is currently adding missing routines, <https://github.com/llvm/llvm-project/issues/93566> 
        
           let has_reliable_f16_math = has_reliable_f16 
        
               && match (target_arch.as_str(), target_os.as_str()) { 
        
                   // FIXME: Disabled on Miri as the intrinsics are not implemented yet. 
        
                   _ if is_miri => false, 
        
                   // x86 has a crash for `powi`: <https://github.com/llvm/llvm-project/issues/105747> 
        
                   ("x86" | "x86_64", _) => false, 
        
                   // Assume that working `f16` means working `f16` math for most platforms, since 
        
                   // operations just go through `f32`. 
        
                   _ => true, 
        
               }; 
        
           let has_reliable_f128_math = has_reliable_f128 
        
               && match (target_arch.as_str(), target_os.as_str()) { 
        
                   // FIXME: Disabled on Miri as the intrinsics are not implemented yet. 
        
                   _ if is_miri => false, 
        
                   // LLVM lowers `fp128` math to `long double` symbols even on platforms where 
        
                   // `long double` is not IEEE binary128. See 
        
                   // <https://github.com/llvm/llvm-project/issues/44744>. 
        
                   // 
        
                   // This rules out anything that doesn't have `long double` = `binary128`; <= 32 bits 
        
                   // (ld is `f64`), anything other than Linux (Windows and MacOS use `f64`), and `x86` 
        
                   // (ld is 80-bit extended precision). 
        
                   ("x86_64", _) => false, 
        
                   (_, "linux") if target_pointer_width == 64 => true, 
        
                   _ => false, 
        
               }; 
        
           if has_reliable_f16 { 
        
               println!("cargo:rustc-cfg=reliable_f16"); 
        
           } 
        
           if has_reliable_f128 { 
        
               println!("cargo:rustc-cfg=reliable_f128"); 
        
           } 
        
           if has_reliable_f16_math { 
        
               println!("cargo:rustc-cfg=reliable_f16_math"); 
        
           } 
        
           if has_reliable_f128_math { 
        
               println!("cargo:rustc-cfg=reliable_f128_math"); 
        
           }

. Each LLVM bump makes a few more things work, but a few of the still-failing platforms do get tested in CI.

tgross35 · 2025-01-28T08:53:43Z

@bors r=workingjubilee,tgross35

bors · 2025-01-28T08:53:45Z

📌 Commit 3d6c6fa has been approved by workingjubilee,tgross35

It is now in the queue for this repository.

rustbot assigned ibraheemdev Jan 24, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 24, 2025

hkBst changed the title ~~Document powf and powi values that are always 1.0~~ Document powf and powi values that are always 1.0 (f64) Jan 24, 2025

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matthiaskrgr mentioned this pull request Jan 24, 2025

Document powf and powi values that are always 1.0 (f32) #136013

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Document powf and powi values that are always 1.0 (f16) #136014

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Document powf and powi values that are always 1.0 (f128) #136015

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workingjubilee assigned workingjubilee and unassigned ibraheemdev Jan 24, 2025

workingjubilee added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 24, 2025

workingjubilee changed the title ~~Document powf and powi values that are always 1.0 (f64)~~ Document powf and powi values that are always 1.0 Jan 24, 2025

hkBst force-pushed the patch-22 branch from 98ff927 to 5297fc1 Compare January 26, 2025 12:40

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Rollup of 9 pull requests #136165

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Rollup of 7 pull requests #136169

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hkBst force-pushed the patch-22 branch from 5297fc1 to a96f6db Compare January 28, 2025 06:58

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Document powf and powi calls that always return 1.0

3d6c6fa

hkBst force-pushed the patch-22 branch from a96f6db to 3d6c6fa Compare January 28, 2025 07:26

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 28, 2025

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Rollup of 9 pull requests #136184

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Rollup of 8 pull requests #136185

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bors merged commit 9a192b2 into rust-lang:master Jan 28, 2025
6 checks passed

rustbot added this to the 1.86.0 milestone Jan 28, 2025

hkBst deleted the patch-22 branch February 2, 2025 12:56

	// Emit these on platforms that have no known ABI bugs, LLVM selection bugs, lowering bugs,
	// missing symbols, or other problems, to determine when tests get run.
	// If more broken platforms are found, please update the tracking issue at
	// <https://github.com/rust-lang/rust/issues/116909>
	//
	// Some of these match arms are redundant; the goal is to separate reasons that the type is
	// unreliable, even when multiple reasons might fail the same platform.
	println!("cargo:rustc-check-cfg=cfg(reliable_f16)");
	println!("cargo:rustc-check-cfg=cfg(reliable_f128)");

	// This is a step beyond only having the types and basic functions available. Math functions
	// aren't consistently available or correct.
	println!("cargo:rustc-check-cfg=cfg(reliable_f16_math)");
	println!("cargo:rustc-check-cfg=cfg(reliable_f128_math)");

	let has_reliable_f16 = match (target_arch.as_str(), target_os.as_str()) {
	// We can always enable these in Miri as that is not affected by codegen bugs.
	_ if is_miri => true,
	// Selection failure <https://github.com/llvm/llvm-project/issues/50374>
	("s390x", _) => false,
	// Unsupported <https://github.com/llvm/llvm-project/issues/94434>
	("arm64ec", _) => false,
	// MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
	("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
	// Infinite recursion <https://github.com/llvm/llvm-project/issues/97981>
	("csky", _) => false,
	("hexagon", _) => false,
	("loongarch64", _) => false,
	("mips" \| "mips64" \| "mips32r6" \| "mips64r6", _) => false,
	("powerpc" \| "powerpc64", _) => false,
	("sparc" \| "sparc64", _) => false,
	("wasm32" \| "wasm64", _) => false,
	// `f16` support only requires that symbols converting to and from `f32` are available. We
	// provide these in `compiler-builtins`, so `f16` should be available on all platforms that
	// do not have other ABI issues or LLVM crashes.
	_ => true,
	};

	let has_reliable_f128 = match (target_arch.as_str(), target_os.as_str()) {
	// We can always enable these in Miri as that is not affected by codegen bugs.
	_ if is_miri => true,
	// Unsupported <https://github.com/llvm/llvm-project/issues/94434>
	("arm64ec", _) => false,
	// Selection bug <https://github.com/llvm/llvm-project/issues/96432>
	("mips64" \| "mips64r6", _) => false,
	// Selection bug <https://github.com/llvm/llvm-project/issues/95471>
	("nvptx64", _) => false,
	// ABI bugs <https://github.com/rust-lang/rust/issues/125109> et al. (full
	// list at <https://github.com/rust-lang/rust/issues/116909>)
	("powerpc" \| "powerpc64", _) => false,
	// ABI unsupported <https://github.com/llvm/llvm-project/issues/41838>
	("sparc", _) => false,
	// Stack alignment bug <https://github.com/llvm/llvm-project/issues/77401>. NB: tests may
	// not fail if our compiler-builtins is linked.
	("x86", _) => false,
	// MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
	("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
	// There are no known problems on other platforms, so the only requirement is that symbols
	// are available. `compiler-builtins` provides all symbols required for core `f128`
	// support, so this should work for everything else.
	_ => true,
	};

	// Configure platforms that have reliable basics but may have unreliable math.

	// LLVM is currently adding missing routines, <https://github.com/llvm/llvm-project/issues/93566>
	let has_reliable_f16_math = has_reliable_f16
	&& match (target_arch.as_str(), target_os.as_str()) {
	// FIXME: Disabled on Miri as the intrinsics are not implemented yet.
	_ if is_miri => false,
	// x86 has a crash for `powi`: <https://github.com/llvm/llvm-project/issues/105747>
	("x86" \| "x86_64", _) => false,
	// Assume that working `f16` means working `f16` math for most platforms, since
	// operations just go through `f32`.
	_ => true,
	};

	let has_reliable_f128_math = has_reliable_f128
	&& match (target_arch.as_str(), target_os.as_str()) {
	// FIXME: Disabled on Miri as the intrinsics are not implemented yet.
	_ if is_miri => false,
	// LLVM lowers `fp128` math to `long double` symbols even on platforms where
	// `long double` is not IEEE binary128. See
	// <https://github.com/llvm/llvm-project/issues/44744>.
	//
	// This rules out anything that doesn't have `long double` = `binary128`; <= 32 bits
	// (ld is `f64`), anything other than Linux (Windows and MacOS use `f64`), and `x86`
	// (ld is 80-bit extended precision).
	("x86_64", _) => false,
	(_, "linux") if target_pointer_width == 64 => true,
	_ => false,
	};

	if has_reliable_f16 {
	println!("cargo:rustc-cfg=reliable_f16");
	}
	if has_reliable_f128 {
	println!("cargo:rustc-cfg=reliable_f128");
	}
	if has_reliable_f16_math {
	println!("cargo:rustc-cfg=reliable_f16_math");
	}
	if has_reliable_f128_math {
	println!("cargo:rustc-cfg=reliable_f128_math");
	}

Document powf and powi values that are always 1.0 #136012

Document powf and powi values that are always 1.0 #136012

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