Delta Transforms

The XorDelta and FloatDelta transforms perform cross-tensor residual encoding. They subtract a reference plane (from a dependency tensor) from the current plane to produce a highly compressible residual.

XorDelta

XorDelta computes a byte-level XOR residual (residual[i] = current[i] ^ reference[i]).

Because XOR is involutive, the forward and inverse operations are identical. XorDelta is guaranteed to be byte-exact and lossless for all inputs.

FloatDelta

!WARNINGFloatDelta is marked as DONE_WITH_CONCERNS because it violates PTWM's byte-exact round-trip invariant.

FloatDelta performs an element-wise float subtraction (current - reference).

IEEE 754 floating-point arithmetic does not guarantee that (a - b) + b == a bit-exactly when a - b introduces a rounding error. Therefore, FloatDelta may be slightly lossy (by ~1 ULP). It exists for opportunistic delta encoding where near-identical tensors yield a residual so small that the coding gain outweighs the slight approximation.

References

• Generic Delta Encoding. Wikipedia