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HELP MOD A. Sloman March 1987 <number> mod <number> -> <number> MOD is an infix operator (precedence 2) which returns the "modulus" of the first number with respect to the second. It is partly similar to REM, which returns the remainder. REM is guaranteed to produce a result with the same sign as its first argument, MOD with the same sign as its second argument. So MOD and REM can give different results for negative arguments: 10 mod 3 = 1 (= 10 rem 3) -10 mod 3 = 2 -10 rem 3 = -1 10 mod -3 = -2 10 rem -3 = 1 -10 mod -3 = -1 (= -10 rem -3) 15 mod -5 = -5 15 rem -5 = 0 REM will never return a negative result when its first argument is positive or a positive (non-zero) result when its first argument is negative. MOD returns a result in the interval between its second argument and 0. It can return the lower but not the upper bound of this interval. The definition of mod is, in effect: define 2 x mod y -> result; lvars x y result; x // y -> -> result; if result < 0 then if y >= 0 then y + result else result endif elseif y < 0 then y + result else result endif; enddefine; MOD can now be applied to all non-complex number types i.e. it is not restricted to integers. So: 67.8 mod 11.1 => ** 1.2 33_/8 mod 2 => ** 1_/8 REM but not MOD can be applied to complex numbers. sqrt(-1) mod 5 => ;;; MISHAP - REAL NUMBER(S) NEEDED ;;; INVOLVING: 0 0.0_+:1.0 ;;; DOING : < mod compile MOD needs to check its arguments. If you know they are going to be integers, you can use the fast_integer version FI_MOD instead. See REF * FASTPROCS and HELP * EFFICIENCY. See REF * NUMBERS for details of POP-11 number types and mathematical operations. See also HELP * MATH - for a summary of mathematical operations POP-11 * DIV - division operator for integers only * REM - remainder -----<Copyright University of Sussex 1987. All rights reserved.>-------