[all-commits] [llvm/llvm-project] f36331: [APFloat] Add support for f8E4M3 IEEE 754 type (#9...

[Alexander Pivovarov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f36331770267501e157ac34afc3ca7d7a0bfb52c
      https://github.com/llvm/llvm-project/commit/f36331770267501e157ac34afc3ca7d7a0bfb52c
  Author: Alexander Pivovarov <pivovaa at amazon.com>
  Date:   2024-07-17 (Wed, 17 Jul 2024)

  Changed paths:
    M clang/include/clang/AST/Stmt.h
    M clang/lib/AST/MicrosoftMangle.cpp
    M llvm/include/llvm/ADT/APFloat.h
    M llvm/lib/Support/APFloat.cpp
    M llvm/unittests/ADT/APFloatTest.cpp

  Log Message:
  -----------
  [APFloat] Add support for f8E4M3 IEEE 754 type (#97179)

This PR adds `f8E4M3` type to APFloat.

`f8E4M3` type  follows IEEE 754 convention

```c
f8E4M3 (IEEE 754)
- Exponent bias: 7
- Maximum stored exponent value: 14 (binary 1110)
- Maximum unbiased exponent value: 14 - 7 = 7
- Minimum stored exponent value: 1 (binary 0001)
- Minimum unbiased exponent value: 1 − 7 = −6
- Precision specifies the total number of bits used for the significand (mantisa), 
    including implicit leading integer bit = 3 + 1 = 4
- Follows IEEE 754 conventions for representation of special values
- Has Positive and Negative zero
- Has Positive and Negative infinity
- Has NaNs

Additional details:
- Max exp (unbiased): 7
- Min exp (unbiased): -6
- Infinities (+/-): S.1111.000
- Zeros (+/-): S.0000.000
- NaNs: S.1111.{001, 010, 011, 100, 101, 110, 111}
- Max normal number: S.1110.111 = +/-2^(7) x (1 + 0.875) = +/-240
- Min normal number: S.0001.000 = +/-2^(-6)
- Max subnormal number: S.0000.111 = +/-2^(-6) x 0.875 = +/-2^(-9) x 7
- Min subnormal number: S.0000.001 = +/-2^(-6) x 0.125 = +/-2^(-9)
```

Related PRs:
- [PR-97118](https://github.com/llvm/llvm-project/pull/97118) Add f8E4M3
IEEE 754 type to mlir



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