min, max, abs and sgn

A pump accepts Setting from 0 to 10. If your program computes 14, that is pointless at best, at −3 maybe worse. Instead of catching every case with a jump, you simply limit the value.

min and max#

Sounds backwards but is logical: with min you set an upper limit, with max a lower limit.

min r0 r0 10         # at most 10
max r0 r0 0          # at least 0

After these two lines r0 is safely between 0 and 10. You find the smallest of three values in two steps: min r3 r0 r1, then min r3 r3 r2.

abs: the distance#

abs drops the sign. −3 becomes 3, 3 stays 3. That way you ask for the distance to the target, whatever the direction:

sub r1 r0 294.15     # deviation from 21 C
abs r2 r1            # how far off, without direction
slt r3 r2 2          # 1 = less than 2 degrees off

sgn: the direction#

sgn returns only the sign: −1 for negative, 1 for positive, 0 for exactly zero. On a display that becomes an arrow: −1 means “too cold”, 1 means “too warm”.

Together: a limited output#

sub r4 294.15 r0     # how much is missing to 21 C?
mul r4 r4 2          # 2 litres per degree
max r4 r4 0          # never negative
min r4 r4 10         # never above 10
s d3 Setting r4