The secret handshake

Two friends send each other a secret handshake as a number. Only the low five bits count:

• bit 0 (1): wave
• bit 1 (2): nod
• bit 2 (4): wink
• bit 3 (8): clap
• bit 4 (16): do the actions in reverse order

The starter reads the number into code_r and holds the five strings. Print the action for each set bit among bits 0 to 3, one per line, lowest bit first. When bit 4 is set, print them highest bit first instead. Bits above bit 4 mean nothing. When none of bits 0 to 3 is set, print no handshake.

tstTests bits: ANDs Rn with op2, sets the NZCV flags and throws the result away. Same as ANDS with the zero register as the destination; takes bitmask immediates. works out the AND of two values and sets the flags from it without keeping the result, so tst code_r, 4 then b.neConditional branch (write as B.EQ, B.NE, B.LT, ...). jumps when bit 2 is set. A mask (a value with only the bits you care about set) that walks through 1, 2, 4, 8, or 8, 4, 2, 1, lets one loop test every bit.

With the sample input 11 (binary 01011) the output is:

wave
nod
clap

What is checked

• the actions for the sample input, one per line
• the program exits cleanly
• the bits are tested with tstTests bits: ANDs Rn with op2, sets the NZCV flags and throws the result away. Same as ANDS with the zero register as the destination; takes bitmask immediates.
• the same program gives the right handshake for other numbers, including 0, reversed codes, and a negative number