[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal

MitchAlsup MitchAlsup at aol.com
Thu Aug 8 16:58:16 BST 2019

We are talking about all of this without a point of reference.

Here is what I do know about correctly rounded transcendentals::

My technology for performing transcendentals in an FMAC unit performs a 
power series polynomial calculation.

I can achieve 14 cycle LN2, EXP2 and 19 cycle SIN, COS faithfully rounded 
with coefficient tables which are (essentially) the same size as the 
FDIV/FSQRT seed tables for Newton-Raphson (or Goldschmidt) iterations. FDIV 
will end up at 17 cycles and FSQRT at 23 cycles. This is exactly what 
Opteron FDIV/FSQRT performance was (oh so onog ago). 

If you impose the correctly rounded requirement:: 
a) the size of the coefficient tables grows by 3.5× and 
b) the number of cycles to compute grows by 1.8×
c) the power to compute grows by 2.5×
For a gain of accuracy of about 0.005 ULP

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