Mantissa Zero Strip

The MantissaZeroStrip transform right-shifts every byte in a plane by k bits, safely removing uninformative trailing zeros.

Theory

GPTQ and AWQ-style quantized checkpoints store weights with rounded mantissas. When you dequantize an INT4-quantized weight back into BF16 or FP16, the low bits of its mantissa are exactly zero.

After PTWM runs the standard bit-reorder and byte-split chain, the resulting mantissa plane consists entirely of bytes sharing this uniform run of trailing zeros. Downstream entropy coders cannot automatically exploit this structure; they see an alphabet artificially inflated by a factor of 2^k, which wastes roughly k bits per element.

By shifting the bytes right by k, MantissaZeroStrip shrinks the apparent alphabet, allowing the entropy coder to compress the plane efficiently. The inverse transform left-shifts the bytes by k to reconstruct the exact original values.

Usage

The transform requires a single wire-format parameter k (between 1 and 7) representing the shift width.

At encode time, the transform verifies that every input byte has at least k trailing zeros. If any byte contains non-zero data in those low bits, the transform returns an error and the trial-encoder skips this chain. This protects against information loss on unquantized data.

References

• IEEE Standard for Floating-Point Arithmetic (IEEE 754).