\ fibonacci in FORTH/6000, two ways
\ GLM, October 2026

: FIB ( n -- fib )
  DUP 2 < IF EXIT THEN
  1- DUP 1- RECURSE SWAP RECURSE + ;

: FIBI ( n -- fib )
  DUP 1 < IF EXIT THEN
  0 1 ROT 0 DO TUCK + LOOP DROP ;

." fib(20) naive  = " 20 FIB . CR
." fib(24) naive  = " 24 FIB . CR
." fib(28) iter   = " 28 FIBI . CR

." fib(24) naive, one run: " CLOCK 24 FIB DROP CLOCK SWAP - U. ." us" CR
." fib(28) iter, one run:  " CLOCK 28 FIBI DROP CLOCK SWAP - U. ." us" CR