12 The optional Floating-Point word set

12.6.2.1554 FLNP1 f-l-n-p-one FLOATING EXT

( F: r1 -- r2 ) or ( r1 -- r2 )

r2 is the natural logarithm of the quantity r1 plus one. An ambiguous condition exists if r1 is less than or equal to negative one.

See:

Rationale:

This function allows accurate compilation when its arguments are close to zero, and provides a useful base for the standard logarithmic functions. For example, FLN can be implemented as:

: FLN 1.0E0 F- FLNP1 ;

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