ref: bcfca7787fbf3907569fd35e0785e0030fe5388d dir: /sys/src/libc/68020/tas.s/
TEXT _tas(SB), $0 MOVL $0, R0 MOVL a+0(FP), A0 TAS (A0) BEQ tas_1 MOVL $1, R0 tas_1: RTS