ref: 2334c2bd4f8be1551f7b84d770d97ea4c087d2a3
dir: /sys/src/libc/amd64/memchr.s/
TEXT memchr(SB),$0 MOVL n+16(FP), CX CMPL 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