[llvm] [APFloat] Add APFloat support for E8M0 type (PR #107127)

[Sergey Kozub via llvm-commits]

sergey-kozub wrote:

Note that the Numpy E8M0 dtype (in the JAX repo) is named `float8_e8m0_fnu`
PR link: https://github.com/jax-ml/ml_dtypes/pull/166

Should we also add the `U` suffix (which stands for "unsigned") to the LLVM type name, for consistency?

https://github.com/llvm/llvm-project/pull/107127