Comment by swiftcoder

> things still work if 4-bit floating point is used, though that is 4-bits including the exponent?

It is generally 4 bits amortised across an entire block. This works more like block-based mage compression schemes - you put a bunch of statistically-similar floats into the same block, and use your handful of bits to index into a codebook containing the deltas from a 16/32 bit reference value for the whole block