Q.COS is v3's q48_cos_approx: on |(Q.REDUCE) x|, the even Taylor series
to n = 10. It sets term and sum to 1.0, n to 2 and the sign cell to 0,
then jumps into Q.SIN's loop, so it adds no call level.
Checked bit for bit against v3's q48_cos_approx (ported into the test)
on the same 33 edge angles and 3000 pseudo-random angles as Q.SIN, at
32- and 64-bit cells, optimised and ASan+UBSan (`make test`,
`make sanitize`). Mutating the start index, the start sum, the
alternation or the sign cell each fails 2500+ cosine checks and no sine
checks.
Headroom (data under arg / return): Q.COS 3/2.
Test results on the amd64 host only. This is a development check, not
acceptance (JUSTIFICATION.md section 16).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
