Additional float types #3451

ecnelises · 2023-06-28T17:45:07Z

text/3451-additional-float-types.md

aaronfranke · 2023-06-28T18:22:32Z

text/3451-additional-float-types.md

+# Drawbacks
+[drawbacks]: #drawbacks
+
+Unlike f32 and f64, although there are platform independent implementation of supplementary intrinsics on these types, not every target support the two types natively, with regards to the ABI. Adding them will be a challenge for handling different cases.


Not every platform supports f32 and f64 natively either. For example, RISC-V without the F or D extensions (ex: ISA string of rv64i). This should be mentioned.

Whatever emulation Rust already does to support f32 and f64 on systems without native support should similarly happen to emulate f128 on systems without native quadruple-precision support.

For riscv without hardware float support there is a defined soft-float ABI. There is not for f16/bf16. Same for x86_64. Many other architectures likely don't have a defined soft-float abi for f128 either. And as I understand it AArch64 doesn't have a soft-float abi at all as Neon support is mandatory and floats are even allowed inside the kernel unlike eg x86_64 where floats are disabled in the kernel to avoid having to save them on syscalls.

text/3451-additional-float-types.md

clarfonthey · 2023-06-28T18:36:11Z

I'm okay with this for the most part, except that I disagree that f16 and f128 should only be limited to targets that support them natively. I think that having target features for float support is a good idea, especially considering how it would help the current situation with floating-point operations in libcore, but I don't think that actually using these types should be gated behind hardware support.

A good example of this is u128, which is not natively supported on many platforms, but still available regardless of target. We can still emulate it, and we can still use it, therefore we can define methods for it. IMHO, gating these types behind target features just adds unnecessary boilerplate for libraries wanting to implement methods for them, and people who are writing performance-sensitive code will already take into account whether these types are fast on the relevant targets before using them.

Additionally, while I don't feel too strongly about it, I don't like the idea of naming the x86 "long double" type f80, since it implies that it's also part of the IEEE 754 standard when it's not. I'm not too against it, though, since it is specific to std::arch.

lygstate · 2023-06-28T18:38:43Z

I'm okay with this for the most part, except that I disagree that f16 and f128 should only be limited to targets that support them natively. I think that having target features for float support is a good idea, especially considering how it would help the current situation with floating-point operations in libcore, but I don't think that actually using these types should be gated behind hardware support.

A good example of this is u128, which is not natively supported on many platforms, but still available regardless of target. We can still emulate it, and we can still use it, therefore we can define methods for it. IMHO, gating these types behind target features just adds unnecessary boilerplate for libraries wanting to implement methods for them, and people who are writing performance-sensitive code will already take into account whether these types are fast on the relevant targets before using them.

Additionally, while I don't feel too strongly about it, I don't like the idea of naming the x86 "long double" type f80, since it implies that it's also part of the IEEE 754 standard when it's not. I'm not too against it, though, since it is specific to std::arch.

f80 is a lot shorter, easy for literal, we can clarify that only f16 f32 f64 f128 are IEEE 754 standard.

tgross35

I added some more detail in various places, and added core::ffi::c_longdouble (which I'm fairly certain we would want)

text/3451-additional-float-types.md

tgross35 · 2023-06-28T19:03:27Z

text/3451-additional-float-types.md

+# Summary
+[summary]: #summary
+
+This RFC proposes new floating point types `f16` and `f128` into core language and standard library. Also this RFC introduces `f80`, `doubledouble`, `bf16` into `core::arch` for inter-op with existing native code.


Suggested change

This RFC proposes new floating point types `f16` and `f128` into core language and standard library. Also this RFC introduces `f80`, `doubledouble`, `bf16` into `core::arch` for inter-op with existing native code.

This RFC proposes new floating point types `f16` and `f128` into core language and standard

library. Also, this RFC introduces `f80`, `doubledouble`, and `bf16` into `core::arch` for

target-specific support, and `core::ffi::c_longdouble` for FFI interop.

Suggest use these symbols, all start with f prefix that consistence

f128: C _Float128, LLVM fp128, GCC __float128

f16: C _Float16, LLVM half, GCC __fp16

f16b: C++ std::bfloat16_t, LLVM bfloat, GCC __bf16

f80e: LLVM x86_fp80, GCC __float80

f64f64: LLVM ppc_fp128, GCC __ibm128

e means extention, not standard IEEE,

f64f64 is shorter than doubledouble, or maybe f64f64e means not standard

@joshtriplett already proposed f16b a long time ago: https://github.com/joshtriplett/rfcs/blob/f16b/text/0000-f16b.md

And these symbols can be used as literal suffix as is

+1 for f16b in favor over bf16 for consistency, I liked that about @joshtriplett's original proposal.

I don't think we should introduce something like f128x - doubledouble or something like the GCC or LLVM types would be better IMO. Reason being, it's kind of ambiguous and specific to one architecture - PowerPC is even moving away from it. Better to give it an unambigous name since it will be used relatively rarely.

i think we should use bf16 rather than f16b since that is widely recognized whereas f16b isn't, and f64_f64 instead of f128x since it really is 2 f64 values and could be easily emulated on any other architecture (do not use f64x2 since that's already used by Simd<f64, 2>). also f<N>x names are more or less defined by IEEE 754 to be wider than N bits, so e.g. f64x would be approximately any type wider than f64 but less than f128 such as f80, f16x could be the f24 type used by some GPUs for depth buffers. so logically f80x would need to be more than 80 bits and f128x would need to be more than 128 bits.

+1 for f16b in favor over bf16 for consistency, I liked that about @joshtriplett's original proposal.

I don't think we should introduce something like f128x - doubledouble or something like the GCC or LLVM types would be better IMO. Reason being, it's kind of ambiguous and specific to one architecture - PowerPC is even moving away from it. Better to give it an unambigous name since it will be used relatively rarely.

f64f64 is OK, no need the underscore looks like doubledouble, f80e instead f80x if f80x is not acceptable

Still vote for f16b, It's rust specific, we can create relationship between bf16 and f16b in rust, that's won't be a burden.

~~What about f64x2 to indicate it's two f64 glued together?~~

do not use f64x2 since that's already used by Simd<f64, 2>

tgross35 · 2023-06-28T19:16:40Z

text/3451-additional-float-types.md

+
+All operators, constants and math functions defined for `f32` and `f64` in core, are also defined for `f16` and `f128`, and guarded by respective conditional guards.
+
+`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.


Suggested change

`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.

The `f80` type is defined in `core::arch::{x86, x86_64}` as 80-bit extended precision. The `doubledouble`

type is defined in `core::arch::{powerpc, powerpc64}` and represent's PowerPC's non-IEEE double-double

format (two `f64`s used to aproximate `f128`). `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}` and represents the "brain" float, a truncated `f32` with SIMD support on some hardware. These

types do not have literal representation.

When working with FFI, the `core::ffi::c_longdouble` type can be used to match whatever type

`long double` represents in C.

Thanks, I did not add the mention of longdouble yet. More things need to be clarified:

Is there always only 1 long double for each (arch, abi, os) tuple? For example, powerpc64le-unknown-linux-gnu can use either double or doubledouble or IEEE binary128 as long double by -mabi=(ieee|ibm)longdouble and -mlong-double-(64|128).

Is mangling of long double the same regardless of its underlying semantics?

Some targets (also powerpc64le for example) support .gnu_attribute, so that linker can differentiate objects compiled by different long double ABI. Should Rust programs using c_longdouble emit such attribute?

text/3451-additional-float-types.md

tgross35 · 2023-06-28T19:45:26Z

text/3451-additional-float-types.md

+
+`f128` is available for on targets having (1) hardware instructions or software emulation for 128-bit float type; (2) backend support for `f128` type on the target; (3) essential target features enabled (if any).
+
+The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.


Suggested change

The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.

The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.

`x86_64-*` and `aarch64-*`

I don't know for sure what targets support it, but we should aim to at least support the major 64-bit CPUs
here at first

There is also a risc target per @aaronfranke here #2629 (comment) but I'm not sure how rv64gQc maps to our riscv64gc

text/3451-additional-float-types.md

tgross35 · 2023-06-28T19:53:47Z

I agree with the comments about f80; I think I would rather see it named x86_fp80 (to match the LLVM intrinsic) to make it clear that it is not a standard type and to discourage use.

A good comment from the issue thread that summed this up: #2629 (comment)

programmerjake · 2023-06-28T19:56:10Z

text/3451-additional-float-types.md

+
+All operators, constants and math functions defined for `f32` and `f64` in core, are also defined for `f16` and `f128`, and guarded by respective conditional guards.
+
+`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.


bf16 is supported on a wide range of newer architectures, such as powerpc, x86, arm, and (WIP) risc-v. imho it should not be classified as architecture-specific but instead more like f16

Yeap bf16 should be simulated when target arch is not supported

thomcc · 2023-06-28T20:16:57Z

Note that supporting 80-bit floats (at all) might complicate the situation being discussed in rust-lang/rust#113053, which suggests that we might be able to manipulate the control word (to set a 53 bit mantissa) in order to get more consistent behavior for f64.

the8472 · 2023-06-28T20:24:27Z

Would it make sense to consider a subset? Especially the 16bit floats are a growing field compared to the legacy types.

tgross35 · 2023-06-29T00:13:49Z

I started trying to get together a better collection of what platforms & features support the different types to serve as a reference when implementing and help steer choices for this RFC (we can pull the contents in at some point). The doc is editable (if logged in), please add info & links if you know of any: https://hackmd.io/@8W5l8q6-Qyyn_vKh2-L0RQ/rJpZsmcdh/edit

Also, zulip thread for this RFC: https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/f16.20.26.20f128.20RFC

programmerjake · 2023-06-29T00:56:16Z

note that PowerISA's BFP128 extension has a specific instruction to aid emulation of f80: xsrqpxp

kpreid · 2023-06-29T18:17:37Z

I'm okay with this for the most part, except that I disagree that f16 and f128 should only be limited to targets that support them natively.

+1 — GPU programming may involve storing and copying f16s without necessarily performing any arithmetic on them except possibly a final conversion to/from f32. Therefore it will be useful to be able to have the guaranteed type even if it has no supported arithmetic operations, simply for interoperability between crates that interact with [f16] slices copied or mapped from the GPU.

Muon · 2023-06-29T18:48:06Z

Note that supporting 80-bit floats (at all) might complicate the situation being discussed in rust-lang/rust#113053, which suggests that we might be able to manipulate the control word (to set a 53 bit mantissa) in order to get more consistent behavior for f64.

I would not say that it complicates anything. It's just another setting of the control word. In any case, such concerns are to be addressed in LLVM, not rustc. If my suggested changes are implemented and accepted, rustc doesn't need to change anything.

Also I wholeheartedly support the 80 bit support. It makes life a lot nicer working with the x87. Though I agree that the name should make clear that it's not an IEEE format.

I also agree that f16 and f128 should be emulated if necessary. Consistent universal support is invaluable.

aaronfranke · 2023-06-29T21:55:46Z

@the8472 If it helped with acceptance, I think splitting f16 and f128 to get those merged in faster would be very welcome. There is less to be debated with those, their behavior is highly standardized by IEEE, they are desired on all platforms, and their names are obvious, so the main challenge is implementation. The others have complexity that needs debate including interop with other languages and if they should be available on all platforms.

joshtriplett · 2023-06-29T22:19:09Z

Also I wholeheartedly support the 80 bit support. It makes life a lot nicer working with the x87. Though I agree that the name should make clear that it's not an IEEE format.

Agreed, though I definitely think it should stay in arch as a target-specific type.

By contrast, I think f16b (or whatever we end up calling it) should be available on all targets, like f16 and f128.

workingjubilee · 2023-06-30T05:53:04Z

I agree that we should basically consider f128 and f16 separately from the rest, especially as "long double" has a bunch of thorny "gotchas" around its repr, e.g. on systems with the x87 FPU it is not guaranteed that C's "long double" is indeed the fully extended 80-bit float.

RalfJung · 2023-06-30T12:16:15Z

text/3451-additional-float-types.md

+
+All operators, constants and math functions defined for `f32` and `f64` in core, are also defined for `f16` and `f128`, and guarded by respective conditional guards.
+
+`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.


For people that have never heard of bf16 or doubledouble (which I assume are 16 and 128 bits in size, respectively), it would be good to link to some sort of document explaining them, and how they differ from f16 and f128, respectively.

Also the RFC needs to say what their semantics are, if IEEE doesn't specify them.

nobody seems to agree on bf16 semantics:
arm has both round as normal with subnormals supported and round to odd with subnormals not supported.
x86 has round to nearest with subnormals not supported.
powerpc has round as normal with subnormals supported.
all isas have round towards zero with subnormals supported (just f32::to_bits(v) >> 16).

clarfonthey · 2023-06-30T19:35:21Z

Since a lot of people are sort of dancing around it, here's my take on a precise proposal for how to modify the RFC:

f16 and f128 should be unconditionally added to the language with the same semantics as existing f32 and f64.
There should be a minimal alias for c_longdouble in the core::ffi module, but its semantics should be explicitly dialed back for the time being.

For f16 and f128 semantics, it should support the generic {float} literals as well as explicit suffixes. They should support basic arithmetic operations via core, and advanced arithmetic operations via std. This can be tweaked as the semantics for f32 and f64 are further refined.

For c_longdouble, we should ensure that From conversions always exist from f16, f32, and f64, which will always happen for f128 but might additionally be required for things like the non-standard 80-bit floats. However, beyond that and ABI compatibility, I don't think anything else should be offered initially. We can eventually export all possible versions of this in core::arch, but for now, the only cases where it should work perfectly should be when it corresponds to f64 or f128; all other cases should be effectively an opaque type as far as most users are concerned.

It should be relatively easy to add in other non-standard float types as experimental in the meantime. My proposal is that these should work very similarly to how I present c_longdouble here: they should have some sense of ABI compatibility with C, and From conversions should be added whenever possible, but no arithmetic until we nail down the semantics. People can implement their own versions with inline assembly and other unsafe code in the meantime, but at least crates can all agree on what the types are.

My suspicion for something like bf16 is that it would be already quite useful if people just had methods to truncate f32 values into it, since this is very fast and it's what bf16 was designed for. This would require some sense of how we want to do "truncating conversion" in general (right now as is the only reasonable method, but we want to generalise that to a trait), but deciding on how those conversions work isn't necessary to simply add the type in an unstable way.

EDIT: Since it's worth adding this after the fact, I wanted to explain a little bit more on why I think these dialed-back semantics are important. Right now, the biggest issue with floating-point semantics is how values are affected by arithmetic operations, like whether NaN payloads are preserved or how rounding is done. However, the one thing we do know about these formats is how you interpret a single value in memory, and that's why we can easily convert to and from these formats to IEEE 754, either exactly or by truncating. This should let us still create a standard type that is ABI-compatible with C (± any nonstandard extensions for particularly weird formats) without actually taking a firm stance on the semantics quite yet.

The other big question about semantics is how the exact values in memory are preserved between operations, particularly the NaN payloads, although that has largely been decided with the stabilisation of total_cmp and from_bits/to_bits on the existing float types. So, it wouldn't be that out of the question to simply support storing these types to their exact specs, quirky payloads and all, while letting end users decide how the actual arithmetic operations behave.

Larsouille25 · 2023-07-01T15:16:11Z

is there a real demand for f16 ? Because, yes there just 2 bytes long but f16 are not very precise

aaronfranke · 2023-07-01T17:49:14Z

@Larsouille25 f16 is useful when you want to store a lot of float data with minimal size, and don't need much precision. For example, floating-point HDR images can be stored in f16, the 10-bit mantissa being more precision bits than the standard 8-bit 0-255 range, and the 5-bit exponent being more than enough. See EXR and formats RGBAh, RGh, Rh.

Another example, quantized mesh data, for some use cases of meshes you really don't care if a vertex is a fraction of a millimeter off, and meshes have a lot of vertices, so using f16 can half the required memory size.

clarfonthey · 2023-07-01T23:21:56Z

Also adding onto what @aaronfranke said, in general, values between 0 and 1 are quite precise for f16s, since they have a 10-bit significand. These values not only are useful for colour, but loads of different things only need to store a float in this range and using up half the memory is quite a benefit.

aaronfranke · 2023-07-02T06:42:03Z

I opened #3453 which is mostly a subset of this RFC, a lot of text was copied from here. It only includes f16 and f128, and changes them to be available on all targets instead of conditionally available.

Nemo157 · 2023-07-02T10:33:27Z

Prior art should also mention https://crates.io/crates/half, which is at ~2million downloads/month, showing there is a lot of demand for f16 (I'm not sure if there's a similar crate for f128).

aaronfranke · 2023-07-02T16:53:15Z

@Nemo157 There is already a link to https://github.com/starkat99/half-rs but a crate link may be better.

Nemo157 · 2023-07-02T17:23:44Z

Ah, under alternatives. I only checked the prior art section (and I think highlighting the wide usage in the RFC would be useful).

tgross35 · 2023-07-02T23:21:47Z

I opened #3453 which is mostly a subset of this RFC, a lot of text was copied from here. It only includes f16 and f128, and changes them to be available on all targets instead of conditionally available.

With this in mind, it would probably be good to shave f16 and f128 out of this RFC and make this only about the compatibility types in core::arch / core::ffi. And bf16, wherever that may end up (side note: the link to Josh's bf16 proposal in this RFC should go to the PR #2690 and not to the file on the branch).

lygstate · 2023-07-03T05:28:14Z

@tgross35 Your link is broken, I updated a new one https://hackmd.io/8Ptau058RmGqV0ZYJ49S9A

tgross35 · 2023-07-03T05:31:05Z

Thank you, formatting fixed: https://hackmd.io/@8W5l8q6-Qyyn_vKh2-L0RQ/rJpZsmcdh

ecnelises · 2023-07-03T16:24:13Z

I opened #3453 which is mostly a subset of this RFC, a lot of text was copied from here. It only includes f16 and f128, and changes them to be available on all targets instead of conditionally available.

I'm still doubting if it's feasible to support it on all platforms. From the view of backend (LLVM, more especially), half and fp128 are not always 'implemented' or even 'defined'.

(let F be either f16 and f128)

If target supports instructions for F, everything is okay.
If target ABI supports software emulation for F, everything is okay.
If target ABI does NOT support software emulation for F, but there's another type with same storage (size/alignment), could it be used as storage type of F (and sure, F is storage-only in such case)? This may cause ABI compatibility issue.
If target ABI does NOT support emulation for F, and no such type exists as storage-only equivalent. We can do nothing here.
If target ABI supports F, but backend (LLVM, etc.) does not implemented the feature, should compiler also have some guard about it?

lygstate · 2023-07-03T16:28:45Z

I opened #3453 which is mostly a subset of this RFC, a lot of text was copied from here. It only includes f16 and f128, and changes them to be available on all targets instead of conditionally available.

I'm still doubting if it's feasible to support it on all platforms. From the view of backend (LLVM, more especially), half and fp128 are not always 'implemented' or even 'defined'.

(let F be either f16 and f128)

If target supports instructions for F, everything is okay.

If target ABI supports software emulation for F, everything is okay.

If target ABI does NOT support software emulation for F, but there's another type with same storage (size/alignment), could it be used as storage type of F (and sure, F is storage-only in such case)? This may cause ABI compatibility issue.

If target ABI does NOT support emulation for F, and no such type exists as storage-only equivalent. We can do nothing here.

If target ABI supports F, but backend (LLVM, etc.) does not implemented the feature, should compiler also have some guard about it?

don't worry, C++ already have both f16 and f128, that is std::float16_t, std::float32_t, std::float64_t, std::float128_t, std::bfloat16_t

aaronfranke · 2023-07-03T16:30:42Z

@ecnelises This is a good question, but I disagree about this point:

If target ABI does NOT support emulation for F, and no such type exists as storage-only equivalent. We can do nothing here.

Yes, we can do something here. There is no reason we can't support our own emulation. Any calculation can be performed on a turing-complete computer. The specific details may be a challenge to implementers in some cases, but it is not impossible to support these types everywhere, therefore they should be supported everywhere.

- Rename doubledouble to f64f64 - Add architecture info about x86 and arm (as suggested) - Add description to target related types (as suggested) - Add link to IEEE-754 and LLVM LangRef

ecnelises · 2023-07-03T17:28:58Z

@ecnelises This is a good question, but I disagree about this point:

If target ABI does NOT support emulation for F, and no such type exists as storage-only equivalent. We can do nothing here.

Yes, we can do something here. There is no reason we can't support our own emulation. Any calculation can be performed on a turing-complete computer. The specific details may be a challenge to implementers in some cases, but it is not impossible to support these types everywhere, therefore they should be supported everywhere.

If we do plan to implement the types everywhere, the 4 becomes 5. Even no has_f128 guards need to exist, compiler should still provide useful diagnostics if the types are used but not implemented by backend yet.

don't worry, C++ already have both f16 and f128, that is std::float16_t, std::float32_t, std::float64_t, std::float128_t, std::bfloat16_t

I think they're optional? https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1467r4.html

scottmcm · 2023-07-06T06:16:23Z

Overall, I like the idea of separating out the real IEEE types from the random stuff, and making f16 and f128 not arch-specific.

f80 is a lot shorter, easy for literal, we can clarify that only f16 f32 f64 f128 are IEEE 754 standard.

I don't think that's important for a niche type, though. It doesn't need a name any nicer than __m512i and friends get.

For that matter, what's the goal of having a type for x87's weird things? It's mentioned in neither the Motivation nor the Rationale sections. How much new Rust code is going to be written targeting those types specifically instead of normal doubles? What's the size and alignment of such a type in memory? Are modern chips putting any effort into making it work efficiently, when x87 (and MMX) tend to be avoided by modern compilers?

bf16 [...] These types do not have literal representation.

Why not? It seems odd to me that f16 would support literals but bf16 wouldn't.

Unless "these types" is supposed to be after a newline so it refers to all the arch-specific ones, maybe?

Jules-Bertholet · 2023-07-07T15:59:58Z

For that matter, what's the goal of having a type for x87's weird things?

One possibility I could see, is that if Rust some day decides to accept the performance hit and make f64 fully IEEE-compliant on no-SSE x86-32, f80 would allow code that doesn't need full compliance to recover some performance on these platforms.

tgross35 · 2023-07-07T17:28:03Z

@ecnelises would you be able to update this RFC to be about bf16, ppc_fp128 and x86_fp80, and reference #3453 as a subset that should be developed first? Specifically, update the PR title to specifically mention those types, and add a link to the other RFC.

We can work on both RFCs in parallel but readers need to be clear about what the relationship between the two is - it's currently ambiguous.

This revision also contains comments addressed from reviewers in RFC rust-lang#3451.

ecnelises · 2023-07-10T16:49:17Z

@ecnelises would you be able to update this RFC to be about bf16, ppc_fp128 and x86_fp80, and reference #3453 as a subset that should be developed first? Specifically, update the PR title to specifically mention those types, and add a link to the other RFC.

We can work on both RFCs in parallel but readers need to be clear about what the relationship between the two is - it's currently ambiguous.

Thanks for your and other's comments. I generally agree that a proposal for IEEE-754 compliant f16/f128 and for target specific types are quite different. So I created another one #3456, focusing on bf16, f64f64, f80 and c_longdouble types.

I'm not familiar with Rust community's RFC policy. So I'm in doubt whether kicking off new post directly from another people without previous commit/author information shows enough respect to the original author.

tgross35 · 2023-07-11T20:31:21Z

Thanks for your and other's comments. I generally agree that a proposal for IEEE-754 compliant f16/f128 and for target specific types are quite different. So I created another one #3456, focusing on bf16, f64f64, f80 and c_longdouble types.

I'm not familiar with Rust community's RFC policy. So I'm in doubt whether kicking off new post directly from another people without previous commit/author information shows enough respect to the original author.

There is no policy on this, but consulting before splitting off your PR would have been, well, nice. It would probably be good for the two RFC authors to come to consensus on Zulip about what the relationship among these RFCs should be, and how to harmonize them a bit (or even figure out coauthoring) to help give the community a better picture of what exactly is being proposed. There is an existing floats rfc topic that can be used for discussion https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/f16.20.26.20f128.20RFC

ecnelises · 2023-08-08T07:09:35Z

I think we can close this since #3456 and #3453 were splitted.

ecnelises added 2 commits June 29, 2023 01:41

Create 0000-additional-float-types.md

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Give RFC number

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ecnelises mentioned this pull request Jun 28, 2023

Suggestions for additional floating-point types #2629

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ehuss added the T-lang Relevant to the language team, which will review and decide on the RFC. label Jun 28, 2023

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aaronfranke mentioned this pull request Jul 2, 2023

Add f16 and f128 float types #3453

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Format and update description

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- Rename doubledouble to f64f64 - Add architecture info about x86 and arm (as suggested) - Add description to target related types (as suggested) - Add link to IEEE-754 and LLVM LangRef

Narsil mentioned this pull request Jul 6, 2023

[Tentative] Adding new intrinsics for gemm. starkat99/half-rs#98

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ecnelises added a commit to ecnelises/rust-rfcs that referenced this pull request Jul 10, 2023

Initial draft from rust-lang#3451

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This revision also contains comments addressed from reviewers in RFC rust-lang#3451.

ecnelises mentioned this pull request Jul 10, 2023

Add bf16, f64f64 and f80 types #3456

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ecnelises closed this Aug 8, 2023

Nicceboy mentioned this pull request Aug 20, 2023

REAL type support librasn/rasn#145

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MarkReedZ mentioned this pull request May 31, 2024

Rust has an f16 and bf16 type ashvardanian/SimSIMD#124

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		All operators, constants and math functions defined for `f32` and `f64` in core, are also defined for `f16` and `f128`, and guarded by respective conditional guards.

		`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.

-`f80` type is defined in `core::arch::{x86, x86_64}`. `doubledouble` type is defined in `core::arch::{powerpc, powerpc64}`. `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}`. They do not have literal representation.
+The `f80` type is defined in `core::arch::{x86, x86_64}` as 80-bit extended precision. The `doubledouble`
+type is defined in `core::arch::{powerpc, powerpc64}` and represent's PowerPC's non-IEEE double-double
+format (two `f64`s used to aproximate `f128`). `bf16` type is defined in `core::arch::{arm, aarch64, x86, x86_64}` and  represents the "brain" float, a truncated `f32` with SIMD support on some hardware. These
+types do not have literal representation.
+When working with FFI, the `core::ffi::c_longdouble` type can be used to match whatever type
+`long double` represents in C.


		`f128` is available for on targets having (1) hardware instructions or software emulation for 128-bit float type; (2) backend support for `f128` type on the target; (3) essential target features enabled (if any).

		The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.

	The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.
	The list of targets supporting `f128` type may change over time. Initially, it includes `powerpc64le-*`.
	`x86_64-` and `aarch64-`

Additional float types #3451

Additional float types #3451

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