ref: 6c70026fa4b2ff235f60c883db15f55b4096bf6b
dir: /sys/src/libc/amd64/memchr.s/
TEXT memchr(SB),$0 MOVQ n+16(FP), CX CMPQ CX, $0 JEQ none MOVQ RARG, DI MOVBLZX c+8(FP), AX CLD /* * SCASB is memchr instruction */ REPN; SCASB JEQ found none: MOVL $0, AX RET found: MOVQ DI, AX SUBQ $1, AX RET