CORDIC in table-look up implementation
Baykov Vladimir
The idea of unification of CORDIC and table-lookup is the follo-
wing: taking leftmost m bits of the argument X ( for example for fu-
nction sin X ) and using them as a input address of ROM with capacity
2**m words we can skip the first m iterations and begin from (m+1)-th
iteration taking the table values as the initial values of iterative
variables.
The total number of iterations in that case is (n-m) , where n - word
size. Correspondingly the number of table constants (arctan, ln) de-
creased on m.
We considered and verified that approach for trigonometric, hyperbolic,
and exp and log functions.
That approach can be completed by stopping of iterations on n/2-th
iteration, suggested by T.C.Chen in 1972, and consequent linear inter-
polation. In such case , unifiing that with table-lookup approach
the total number of iteration is (n/2-m).
If for example n=24, m=8 we should execute only 4 iterations.
All the detailed of the implementation of this approach you
can find in the book: Special-purpose processors:iterative algorithms
and structures" (coauthor Vladimir Smolov), Moscow, 1985 and in:
http://devil.ece.utexas.edu/cordic.html
Vladimir Baykov