ref: fa94532c0843b6f2b6e132b762f497b9cc4066f4 dir: /sys/src/libc/amd64/strlen.s/
TEXT strlen(SB),$0 MOVL $0, AX MOVQ $-1, CX CLD /* * look for end of string */ MOVQ RARG, DI REPN; SCASB MOVQ DI, AX SUBQ RARG, AX SUBQ $1, AX RET