riddle - replace 4 strokes of code in equivalent 2

Question

tst r0
blt label
cmp r0, #11
bgt label

As I understand this peace of code is a brench if r0 < 0 or r0 > 11.

How can I optimize it to only 2 strokes of code.

Answer 1

Try unsigned comparison:

cmp r0, #11
bhi label

Values below 0 are represented using two's complement. So, -1 represented as a 16-bit unsigned value is 1111111111111111, which is higher than 11 (which is 0000000000001011).