Forth 2012: FTRUNC

( F: r₁ -- r₂ ) or ( r₁ -- r₂ )

Round r₁ to an integral value using the "round towards zero" rule, giving r₂.

See:

12.3.2 Floating-point operations, 12.6.1.1612 FROUND, 12.6.1.1558 FLOOR.

Implementation:

: FTRUNC ( r1 -- r2 )
         FDUP F0= 0=
   IF    FDUP F0<
   IF    FNEGATE FLOOR FNEGATE
   ELSE   FLOOR
   THEN
   THEN   ;

Testing:

SET-EXACT

T{ -0E          FTRUNC F0= -> <TRUE> }T
T{ -1E-9        FTRUNC F0= -> <TRUE> }T
T{ -0.9E        FTRUNC F0= -> <TRUE> }T
T{ -1E  1E-5 F+ FTRUNC F0= -> <TRUE> }T
T{ 0E           FTRUNC     -> 0E   R}T
T{ 1E-9         FTRUNC     -> 0E   R}T
T{ -1E -1E-5 F+ FTRUNC     -> -1E   R}T
T{ 3.14E        FTRUNC     -> 3E   R}T
T{ 3.99E        FTRUNC     -> 3E   R}T
T{ 4E           FTRUNC     -> 4E   R}T
T{ -4E          FTRUNC     -> -4E   R}T
T{ -4.1E        FTRUNC     -> -4E   R}T