COMMENT compute |R1| ! and place the result in register R1.
ZERO? 1 R1=0
GOTO R1>0
COMMENT R1=0, we are done as 0 ! = 1.
LABEL R1=0
INC 1
GOTO done
COMMENT R1>0, use n ! = 1 x 2 x ... x n
LABEL R1>0
COPY 2 1
ZERO 1
INC 1
ZERO 3
INC 3
COMMENT main loop
LABEL loop
MULT 1 3
EQ? 2 3 done
INC 3
GOTO loop
COMMENT that’s all folks.
LABEL done
QUIT