Tracking issue for #![feature(const_float_bits_conv)]
#72447
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ecstatic-morse
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… r=RalfJung,oli-obk Const floating point bitcasts and classification Makes the `f32` and `f64` methods described in rust-lang#72447 and rust-lang#72505 unstably const. r? @RalfJung
KodrAus
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…=RalfJung Const floating point bitcasts and classification Makes the `f32` and `f64` methods described in rust-lang#72447 and rust-lang#72505 unstably const. r? @RalfJung
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Is there anyway to hard-code this without nightly? |
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pub const NA_REAL: f64 = unsafe {
std::mem::transmute(u64::from_le_bytes([
0xa2, 0x07, 0x00, 0x00, 0x00, 0x00, 0xf0, 0x7f,
]))
};This works for me now. |
Does that issue need to be a blocker for this? The functions in question aren't doing arithmetic on floats, they're just casting bit representations. AIUI while float arithmetic might be nonportable, bit representations are well-specified, yes? |
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Actually, I take that back after looking at #73288 . |
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Is there any reason It might not seem useful to provide just
The 2nd is what I was poking around with, when I realized that I can't actually turn the result into a user-friendly |
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per @burrbull in #57241 (comment) This allows routing around these using |
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With rust-lang/rfcs#3514 having been accepted, I think this is unblocked. I am working on stabilizing |
Rollup merge of rust-lang#129555 - RalfJung:const_float_bits_conv, r=dtolnay stabilize const_float_bits_conv This stabilizes `const_float_bits_conv`, and thus fixes rust-lang#72447. With rust-lang#128596 having landed, this is entirely a libs-only question now. ```rust impl f32 { pub const fn to_bits(self) -> u32; pub const fn from_bits(v: u32) -> Self; pub const fn to_be_bytes(self) -> [u8; 4]; pub const fn to_le_bytes(self) -> [u8; 4] pub const fn to_ne_bytes(self) -> [u8; 4]; pub const fn from_be_bytes(bytes: [u8; 4]) -> Self; pub const fn from_le_bytes(bytes: [u8; 4]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self; } impl f64 { pub const fn to_bits(self) -> u64; pub const fn from_bits(v: u64) -> Self; pub const fn to_be_bytes(self) -> [u8; 8]; pub const fn to_le_bytes(self) -> [u8; 8] pub const fn to_ne_bytes(self) -> [u8; 8]; pub const fn from_be_bytes(bytes: [u8; 8]) -> Self; pub const fn from_le_bytes(bytes: [u8; 8]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self; } ```` Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
stabilize const_float_bits_conv This stabilizes `const_float_bits_conv`, and thus fixes rust-lang/rust#72447. With rust-lang/rust#128596 having landed, this is entirely a libs-only question now. ```rust impl f32 { pub const fn to_bits(self) -> u32; pub const fn from_bits(v: u32) -> Self; pub const fn to_be_bytes(self) -> [u8; 4]; pub const fn to_le_bytes(self) -> [u8; 4] pub const fn to_ne_bytes(self) -> [u8; 4]; pub const fn from_be_bytes(bytes: [u8; 4]) -> Self; pub const fn from_le_bytes(bytes: [u8; 4]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self; } impl f64 { pub const fn to_bits(self) -> u64; pub const fn from_bits(v: u64) -> Self; pub const fn to_be_bytes(self) -> [u8; 8]; pub const fn to_le_bytes(self) -> [u8; 8] pub const fn to_ne_bytes(self) -> [u8; 8]; pub const fn from_be_bytes(bytes: [u8; 8]) -> Self; pub const fn from_le_bytes(bytes: [u8; 8]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self; } ```` Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
stabilize const_float_bits_conv This stabilizes `const_float_bits_conv`, and thus fixes rust-lang/rust#72447. With rust-lang/rust#128596 having landed, this is entirely a libs-only question now. ```rust impl f32 { pub const fn to_bits(self) -> u32; pub const fn from_bits(v: u32) -> Self; pub const fn to_be_bytes(self) -> [u8; 4]; pub const fn to_le_bytes(self) -> [u8; 4] pub const fn to_ne_bytes(self) -> [u8; 4]; pub const fn from_be_bytes(bytes: [u8; 4]) -> Self; pub const fn from_le_bytes(bytes: [u8; 4]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self; } impl f64 { pub const fn to_bits(self) -> u64; pub const fn from_bits(v: u64) -> Self; pub const fn to_be_bytes(self) -> [u8; 8]; pub const fn to_le_bytes(self) -> [u8; 8] pub const fn to_ne_bytes(self) -> [u8; 8]; pub const fn from_be_bytes(bytes: [u8; 8]) -> Self; pub const fn from_le_bytes(bytes: [u8; 8]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self; } ```` Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
stabilize const_float_bits_conv This stabilizes `const_float_bits_conv`, and thus fixes rust-lang/rust#72447. With rust-lang/rust#128596 having landed, this is entirely a libs-only question now. ```rust impl f32 { pub const fn to_bits(self) -> u32; pub const fn from_bits(v: u32) -> Self; pub const fn to_be_bytes(self) -> [u8; 4]; pub const fn to_le_bytes(self) -> [u8; 4] pub const fn to_ne_bytes(self) -> [u8; 4]; pub const fn from_be_bytes(bytes: [u8; 4]) -> Self; pub const fn from_le_bytes(bytes: [u8; 4]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self; } impl f64 { pub const fn to_bits(self) -> u64; pub const fn from_bits(v: u64) -> Self; pub const fn to_be_bytes(self) -> [u8; 8]; pub const fn to_le_bytes(self) -> [u8; 8] pub const fn to_ne_bytes(self) -> [u8; 8]; pub const fn from_be_bytes(bytes: [u8; 8]) -> Self; pub const fn from_le_bytes(bytes: [u8; 8]) -> Self; pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self; } ```` Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
Tracking issue for the
#![feature(const_float_bits_conv)]feature gate, which makes the following methods onf32andf64const fn:#![feature(float_bits_conv)]to_bitsfrom_bits#![feature(float_to_from_bytes)]to_bytes_beto_bytes_leto_bytes_nefrom_bytes_befrom_bytes_lefrom_bytes_neThese require
transmutewithin aconst fnto stabilize, and–unlike the recently stabilized#![feature(const_int_conversion)]–do not have a const-stable alternate implementation. Nevertheless, these may be useful for nightly users.Stabilization is blocked on #57241.
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