MxFp4 Deinterleave

The MxFp4Deinterleave transform explicitly unpacks interleaved microscaled formats (specifically OCP MXFP4).

Theory

The OCP MXFP4 format typically packs data in 32-element blocks consisting of 17 bytes: 16 bytes of packed nibbles (containing 32 4-bit values) and 1 byte of E8M0 scale data.

To effectively compress this layout, the transform deinterleaves the block into two distinct planes:

graph LR
    A[17-byte MXFP4 Block] --> B[16 Bytes<br/>Packed Nibbles]
    A --> C[1 Byte<br/>E8M0 Scale]
    B --> D[VALUE Plane<br/>32 x 4-bit elements]
    C --> E[SCALE Plane<br/>1 x 8-bit element]

Splitting these planes is critical because the nearly uniform random VALUE nibbles require different codecs (like Per-Group Codebook) than the highly correlated SCALE bytes.

Inverse

The inverse operation recombines the two planes, packing every 32 nibbles and 1 scale byte back into the rigid 17-byte interleaved MXFP4 block format.

References

• OCP Microscaling Formats (MX) Specification v1.0. Link