millfork/include/zp_reg.mfk

inline asm byte __mul_u8u8u8() {
    ? LDA #0
    ? JMP __mul_u8u8u8_start
__mul_u8u8u8_add:
    CLC
    ADC __reg.lo
__mul_u8u8u8_loop:
    ASL __reg.lo
__mul_u8u8u8_start:
    LSR __reg.hi
    BCS __mul_u8u8u8_add
    BNE __mul_u8u8u8_loop
    ? RTS
}