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change c_double to f32 on avr targets - #154647

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folkertdev:avr-c_double-f32
Apr 1, 2026
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change c_double to f32 on avr targets#154647
rust-bors[bot] merged 1 commit into
rust-lang:mainfrom
folkertdev:avr-c_double-f32

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@folkertdevfolkertdev commented Mar 31, 2026

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Extracted from #152980. That version also makes this change for msp430 but that is actually incorrect based on https://www.ti.com/lit/ug/slau132r/slau132r.pdf table 5-1 that specifies double as f64.

r? tgross35
cc @Patryk27@workingjubilee

@rustbotrustbot 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 Mar 31, 2026
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tgross35 approved these changes Mar 31, 2026
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This has been on my todo list for a while, thanks!

Note that there are some LLVM bugs related to this. IIRC LLVM's double type (always double precision) will emit calls like sqrt which are of course single precision when it needs to use sqrtf64. Not that many people are running complicated float math on AVR, and that doesn't affect this change in any case.

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@bors r+ rollup

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📌 Commit 2e4c5ca has been approved by tgross35

It is now in the queue for this repository.

@rust-borsrust-borsBot 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 Mar 31, 2026
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⚠️ A new commit de0c9f0df6f0af2600e6fca1b62976dac38ec360 was pushed.

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folkertdev
folkertdev commented Mar 31, 2026
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Comment threadlibrary/core/src/ffi/c_double.md Outdated
Equivalent to C's `double` type.

This type will almost always be [`f64`], which is guaranteed to be an [IEEE 754 double-precision float] in Rust. That said, the standard technically only guarantees that it be a floating-point number with at least the precision of a [`float`], and it may be `f32` or something entirely different from the IEEE-754 standard.
This type will almost always be [`f64`], which is guaranteed to be an [IEEE 754 double-precision float] in Rust. That said, the standard technically only guarantees that it be a floating-point number with at least the precision of a [`float`], and it may be [`f32`] or something entirely different from the IEEE-754 standard.

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should we expclicitly mention avr here? https://doc.rust-lang.org/std/ffi/type.c_int.html does not name specific platforms.

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If anything maybe just say "on some 16-bit targets"? r=me either way

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After discussion in #t-compiler/help > what is `#[doc(cfg(all()))]` I changed this implementation to be more consistent.

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@bors r=tgross35 rollup

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📌 Commit dc9836e has been approved by tgross35

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@rust-borsrust-borsBot 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 31, 2026
@jhprattjhpratt mentioned this pull request Apr 1, 2026
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Auto merge of#154668- jhpratt:rollup-ePnl7Di, r=jhpratt
2bd7a97
Rollup of 4 pull requests
Successful merges:
- #154356 ( Add integer truncation and extension methods)
- #154641 (build_helper: fix yarn locking, add check, and bump lockfile)
- #154647 (change `c_double` to `f32` on `avr` targets)
- #154655 (Fix associated type bound suggestion span issue)
chenyukang added a commit to chenyukang/rust that referenced this pull request Apr 1, 2026
@chenyukang
Rollup merge ofrust-lang#154647- folkertdev:avr-c_double-f32, r=tgr…
735edd8
…oss35
change `c_double` to `f32` on `avr` targets
Extracted from rust-lang#152980. That version also makes this change for `msp430` but that is actually incorrect based on https://www.ti.com/lit/ug/slau132r/slau132r.pdf table 5-1 that specifies `double` as `f64`.
r? tgross35
cc @Patryk27@workingjubilee
@chenyukangchenyukang mentioned this pull request Apr 1, 2026
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rust-borsBot merged commit 1fb655c into rust-lang:mainApr 1, 2026
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@rustbotrustbot added this to the 1.96.0 milestone Apr 1, 2026
rust-timer added a commit that referenced this pull request Apr 1, 2026
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Unrolled build for#154647
3fcd941
Rollup merge of #154647 - folkertdev:avr-c_double-f32, r=tgross35
change `c_double` to `f32` on `avr` targets
Extracted from #152980. That version also makes this change for `msp430` but that is actually incorrect based on https://www.ti.com/lit/ug/slau132r/slau132r.pdf table 5-1 that specifies `double` as `f64`.
r? tgross35
cc @Patryk27@workingjubilee
@Mark-SimulacrumMark-Simulacrum added the relnotes Marks issues that should be documented in the release notes of the next release. label May 11, 2026
@rustbotrustbot mentioned this pull request May 11, 2026
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@BoxyUwUBoxyUwU mentioned this pull request May 12, 2026
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