ref: 00c2c84deabbed8dfe7ed1c5e25af4dd093d3755 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