WP 34S vs. DM42 decimal128 differences?

[Nigel (UK)]

This is addressed to Pauli:

I've noticed that sin (pi radians) in double-precision mode on the WP34S is only correct to 17 significant figures. This disturbs me more than I would have expected (given that I normally have the calculator set to give me answers to 4 sf only!).

If I change SINCOSDIGITS in decn.c to 69, all calculated digits are correct. Trig functions are slower (more so in double precision than in single precision).

If I use 69 digits in the function sincosTaylor() when the calculator is in double precision mode, but 39 digits in single precision, I seem to get the best of both worlds - correct answers in both single and double precision, with no slow-down in single-precision mode.

Is this a change worth making (once I've done some more extensive testing, and looked at the code for tan x as well)? Or is there a downside other than speed to using these extra digits?

Nigel (UK)