ref: 12c9d2fc728b51aa1eb9a70d0d331eb9464912d9 dir: /src/plan9/clz_amd64.s/
TEXT sl_clz(SB),1,$0 BYTE $0x0F; BYTE $0xBD; BYTE $0xC5 /* BSRL RARG, AX */ XORL $31, AX RET