ref: 8b780e3e59ec287937c5754521329840a69b28ee dir: /builtins.arm64.s/
TEXT __builtin_ctz(SB),1,$0 RBITW R0, R0 CLZW R0, R0 RETURN TEXT __builtin_clz(SB),1,$0 CLZW R0, R0 RETURN TEXT __builtin_clzll(SB),1,$0 CLZ R0, R0 RETURN