<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def mix_wave(src, dst):
 """Mix two wave body into one."""

    if len(src) > len(dst):
        # output should be longer
        dst, src = src, dst

    for i, sv in enumerate(src):
        dv = dst[i]
        if sv < 128 and dv < 128:
            dst[i] = int(sv * dv / 128)
        else:
            dst[i] = int(2 * (sv + dv) - sv * dv / 128 - 256)
    return dst