Skip to main content
← Lab

gelufloor

mixedC++ · CPUSystems & data structuresJuly 9, 2026

the question

Is GELU's tanh approximation actually an approximation, in practice?

what came out

It depends on your precision. Its error is 7x below the bf16 rounding floor (free there) but level with the fp16 floor (not free), and it peaks in the shoulder, not the tails. A precision accounting, not a benchmark.

method & receipts

  • Result: mixed
  • Pre-registered the prediction was written down and committed before the run.

→ read the code and re-run it

github.com/v-code01/gelufloor