ref: 0f58e47551345d7c48c9404bc4188f7fc195e51a dir: /sys/src/ape/lib/ap/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