ref: 31e59bb74dcaa3273e93a6585e902df407f17ac6 dir: /src/plan9/clz_amd64.s/
TEXT fl_clz(SB),1,$0 BYTE $0x0F; BYTE $0xBD; BYTE $0xC5 /* BSRL RARG, AX */ XORL $31, AX RET