The problem is that the result of a multiply instruction can be twice as long as its operands. 问题在于乘法指令的结果可能会有其操作数的两倍之长。
Some special instructions added in to enhance the capability of processing complex calculation in embedded CPU were MAC ( multiply accumulate) instruction, PERM ( permutation) instruction, and four transport instructions to transport data. 为了增强嵌入式CPU处理复杂运算的能力,加入特殊指令&乘积累加指令MAC和置换指令PERM。