Bug 239 - FP16 (and FP128) POWER Formal Standard proposal
Summary: FP16 (and FP128) POWER Formal Standard proposal
Status: RESOLVED FIXED
Alias: None
Product: Libre-SOC's first SoC
Classification: Unclassified
Component: Specification (show other bugs)
Version: unspecified
Hardware: PC Linux
: --- enhancement
Assignee: Alain D D Williams
URL: https://libre-soc.org/openpower/sv/sv...
Depends on:
Blocks: 174
  Show dependency tree / graph
 
Reported: 2020-03-13 12:54 GMT by Luke Kenneth Casson Leighton
Modified: 2022-09-30 21:04 BST (History)
1 user (show)

See Also:
NLnet milestone: NLNet.2019.10.046.Standards
total budget (EUR) for completion of task and all subtasks: 2500
budget (EUR) for this task, excluding subtasks' budget: 2500
parent task for budget allocation: 174
child tasks for budget allocation:
The table of payments (in EUR) for this task; TOML format:
addw = {amount=1250, submitted=2022-08-18, paid=2022-08-25} lkcl = { amount = 1250, submitted = 2022-06-25, paid = 2022-07-21 }

Attachments
Add an attachment (proposed patch, testcase, etc.)

Note You need to log in before you can comment on or make changes to this bug.
Description Luke Kenneth Casson Leighton 2020-03-13 12:54:52 GMT 
A formal write-up of the augmentation of POWER ISA to switch on IEEE754 FP16 (also useable for  FP128) is needed, to be proposed to the OpenPOWER Foundation at a later date.
Comment 1 Luke Kenneth Casson Leighton 2020-12-02 15:13:22 GMT 
we may actually do BF16 rather than FP128
Comment 2 Luke Kenneth Casson Leighton 2022-06-25 10:15:20 BST 
this is done, the decision was to go with:

* default: FP64
* 0b01   : FP32
* 0b10   : FP16
* 0b11   : BF16

as part of the element-width overrides in SVP64

## Elwidth for FP Registers:

| Value | Mnemonic       | Description                        |
|-------|----------------|------------------------------------|
| 00    | DEFAULT        | default behaviour for FP operation     |
| 01    | `ELWIDTH=f32`  | 32-bit IEEE 754 Single floating-point  |
| 10    | `ELWIDTH=f16`  | 16-bit IEEE 754 Half floating-point   |
| 11    | `ELWIDTH=bf16` | Reserved for `bf16` |