Returns pi (3.14159265...) at the specified precision.
If the precision is less than or equal to a prior precision,
the earlier calculated value is returned (rounded if needed).
If the specified precision is higher than any previously calculated
precision, then the constant is recalculated and the higher value
is retained for subsequent use.
Repeated calls to the function at the same precision perform no rounding
or calculation.
Returns pi (3.14159265...) at the specified precision. If the precision is less than or equal to a prior precision, the earlier calculated value is returned (rounded if needed). If the specified precision is higher than any previously calculated precision, then the constant is recalculated and the higher value is retained for subsequent use. Repeated calls to the function at the same precision perform no rounding or calculation.