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change c_double to f32 on avr targets

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This commit is contained in:
Folkert de Vries
2026-03-31 21:49:46 +02:00
parent ba11b1e3f0
commit dc9836e29c
2 changed files with 25 additions and 7 deletions
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library/core/src/ffi/c_double.md
+1 -1
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@@ -1,6 +1,6 @@
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`]; some 16-bit systems use [`f32`], for example. Esoteric systems could use something entirely different from the IEEE-754 standard.
[IEEE 754 double-precision float]: https://en.wikipedia.org/wiki/IEEE_754
[`float`]: c_float
library/core/src/ffi/primitives.rs
+24 -6
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@@ -15,24 +15,27 @@ macro_rules! type_alias {
}
}
type_alias! { "c_char.md", c_char = c_char_definition::c_char; #[doc(cfg(all()))] }
// `#[doc(cfg(true))]` is used to prevent rustdoc from displaying a "Available on ..." box.
// The implementation of these constants is target-specific, but every target does define them.
type_alias! { "c_char.md", c_char = c_char_definition::c_char; #[doc(cfg(true))] }
type_alias! { "c_schar.md", c_schar = i8; }
type_alias! { "c_uchar.md", c_uchar = u8; }
type_alias! { "c_short.md", c_short = i16; }
type_alias! { "c_ushort.md", c_ushort = u16; }
type_alias! { "c_int.md", c_int = c_int_definition::c_int; #[doc(cfg(all()))] }
type_alias! { "c_uint.md", c_uint = c_int_definition::c_uint; #[doc(cfg(all()))] }
type_alias! { "c_int.md", c_int = c_int_definition::c_int; #[doc(cfg(true))] }
type_alias! { "c_uint.md", c_uint = c_int_definition::c_uint; #[doc(cfg(true))] }
type_alias! { "c_long.md", c_long = c_long_definition::c_long; #[doc(cfg(all()))] }
type_alias! { "c_ulong.md", c_ulong = c_long_definition::c_ulong; #[doc(cfg(all()))] }
type_alias! { "c_long.md", c_long = c_long_definition::c_long; #[doc(cfg(true))] }
type_alias! { "c_ulong.md", c_ulong = c_long_definition::c_ulong; #[doc(cfg(true))] }
type_alias! { "c_longlong.md", c_longlong = i64; }
type_alias! { "c_ulonglong.md", c_ulonglong = u64; }
type_alias! { "c_float.md", c_float = f32; }
type_alias! { "c_double.md", c_double = f64; }
type_alias! { "c_double.md", c_double= c_double_definition::c_double; #[doc(cfg(true))] }
mod c_char_definition {
crate::cfg_select! {
@@ -183,3 +186,18 @@ mod c_int_definition {
}
}
}
mod c_double_definition {
crate::cfg_select! {
target_arch = "avr" => {
// avr:
// Per https://gcc.gnu.org/wiki/avr-gcc#Type_Layout. The table says `4,8` because
// in C the width of `double` can be changed with the `-mdouble=32/64` setting. But
// 32-bits is the default for the rust avr target.
pub(super) type c_double = f32;
}
_ => {
pub(super) type c_double = f64;
}
}
}