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This PR adds `f4E2M1FN` type to mlir. `f4E2M1FN` type is proposed in [OpenCompute MX Specification](https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf). It defines a 4-bit floating point number with bit layout S1E2M1. Unlike IEEE-754 types, there are no infinity or NaN values. ```c f4E2M1FN - Exponent bias: 1 - Maximum stored exponent value: 3 (binary 11) - Maximum unbiased exponent value: 3 - 1 = 2 - Minimum stored exponent value: 1 (binary 01) - Minimum unbiased exponent value: 1 − 1 = 0 - Has Positive and Negative zero - Doesn't have infinity - Doesn't have NaNs Additional details: - Zeros (+/-): S.00.0 - Max normal number: S.11.1 = ±2^(2) x (1 + 0.5) = ±6.0 - Min normal number: S.01.0 = ±2^(0) = ±1.0 - Min subnormal number: S.00.1 = ±2^(0) x 0.5 = ±0.5 ``` Related PRs: - [PR-95392](https://github.com/llvm/llvm-project/pull/95392) [APFloat] Add APFloat support for FP4 data type - [PR-105573](https://github.com/llvm/llvm-project/pull/105573) [MLIR] Add f6E3M2FN type - was used as a template for this PR - [PR-107999](https://github.com/llvm/llvm-project/pull/107999) [MLIR] Add f6E2M3FN type