You want to copy more one byte at a time (unrolling by 4, 8 or more; and for memset, multiplying the stored value by 0x01010101...). In recent processors rep mo

You want to copy more one byte at a time (unrolling by 4, 8 or more; and for memset, multiplying the stored value by 0x01010101...). In recent processors rep movsb and rep stosb do all that in microcode, and are also able to copy or fill the destination one cache line at a time.