Comments and the three limits

A program you no longer understand after three weeks is a broken program. Comments help against that. But they cost space, and space on the chip is tight.

Comments#

The chip ignores everything from # to the end of the line. A comment may fill a whole line or sit behind an instruction:

# pressure in bar for the hallway display
div r1 r0 100   # 100 kPa = 1 bar

Good comments say why something is the way it is or what a number means. # r1 = r0 / 100 helps nobody, the instruction already says that.

The three limits#

More does not fit on the chip. There is no trick that makes a line “not count”.

Which limit breaks first?#

Do the math: 4096 characters divided by 128 lines is 32 characters per line. An instruction like add r1 r0 273.15 has 16 characters. With a comment behind it you quickly reach 45. That is why with commented programs the character limit is almost always the binding one, not the line count.

# --- conversion for the status panel ---
sub r1 r0 273.15   # Kelvin to degrees C
mul r2 r1 1.8      # Fahrenheit, step 1
add r2 r2 32       # Fahrenheit, step 2

Four lines, a good 140 characters. Only 44 of them are instructions.

When it gets tight#

• Shorten comments, cut filler words. “deg C” instead of “converted to degrees Celsius”.
• Use blank lines sparingly.
• The game version from the last lesson strips comments and blank lines for the chip. You keep the commented version for yourself.
• The IC10 coder always shows lines, characters and width in the bar at the top.