MIPS I 指令立即域 [英] MIPS I instruction immediate field

问题描述

该字段由算术和条件分支指令使用.

The field is used by arithmetic and conditional branch instructions.

第一个问题是:

可以存储在立即算术指令和条件分支中的值的范围是多少?

What would be the range of values which can be stored in an immediate arithmetic instruction and conditional branch?

第二个是:

如果 MIPS 处理器有 64 个寄存器，您将如何更改立即指令格式以引用这些寄存器?我将如何绘制和标记格式?

if a MIPS processor has 64 registers, how would you change the immediate instruction format to reference these registers? How would I draw and label the format?

推荐答案

第 1 部分:

如下图所示:

I-Type 指令为立即数字段保留了 16 位.这当然意味着立即数字段可以采用 2¹⁶ 个可能的值.如果我们考虑立即数字段可以是正数或负数(1 位用于符号)，我们可以看到最大值为 2¹⁵ - 1，最小值为 -(2¹⁵ - 1).

The I-Type instruction has 16 bits reserved for the immediate field. This of course means that the immediate field can take on 2¹⁶ possible values. If we consider that the immediate field can be positive or negative (1 bit is used for the sign) we can see that the max would be 2¹⁵ - 1 and the min would be −(2¹⁵ - 1).

第 2 部分:

再一次，查看上图我们可以看到 rs 和 rt 寄存器被指定为 5 位.这是因为 mips 指令集中有 32 个寄存器——即 2⁵.如果有 64 个寄存器，那么 rs 和 rt 字段都需要 6 位长，因此立即字段只剩下 14 位.

Again, looking at the diagram above we can see that the rs and rt registers are specified with 5 bits. This is because there are 32 registers in the mips instruction set — i.e. 2⁵. If there were instead 64 registers, both the rs and rt fields would need to be 6 bits long, thus leaving only 14 bits for the immediate field.

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