+@ +1 should remain +1
+SSSTN | PUSH +1
+NSTTSSSTN | JSR > 10001 (abs)
+NSTTSSTN | JSR > 1001 (print number from stack)
+
+@ -1 should become +1
+SSTTN | PUSH -1
+NSTTSSSTN | JSR > 10001 (abs)
+NSTTSSTN | JSR > 1001 (print number from stack)
+
+@ 0 should remain 0
+SSSSN | PUSH 0
+NSTTSSSTN | JSR > 10001 (abs)
+NSTTSSTN | JSR > 1001 (print number from stack)
+
+@ Test the most negative number.
+@ It is impossible to return the true absolute value but should return zero.
+SSSTN | PUSH +1
+SSSTTTTTTN | PUSH +63
+NSTTSTTSTN | JSR > 101101 (lshift)
+NSTTSSSTN | JSR > 10001 (abs)
+NSTTSSTN | JSR > 1001 (print number from stack)
+NNN | DIE
+
+#include <logic.pvvs>
+#include <stdio.pvvs>