MIPS ADDIU混乱 [英] MIPS ADDIU confusion

问题描述

我正在单周期MIPS处理器上做作业，对addiu指令有些困惑.

I am doing an assignment on single cycle MIPS processor and I am a little confused on the addiu instruction.

在此网站上，作为我的参考作者指出立即数将被扩展符号

On this website, as my reference the author states that the immediate will be sign extened

Description:
   Adds a register and a sign-extended immediate value and stores the result
   in a register
Operation:
   $t = $s + imm; advance_pc (4);
Syntax:
   addiu $t, $s, imm
Encoding:
   0010 01ss ssst tttt iiii iiii iiii iiii

如果我有以下说明

   lui      $3,0x1001
   addiu    $3,$3,0x8010

然后创建我的数据路径，使符号扩展我会得到的

and I create my data path that sign extends addiu I would get

$3 := 0x1001_0000
$3 := 0x1001_0000 + 0x1111_8010 = 0x1000_8010

但是根据PCSpim的说法，这是不正确的，我应该得到

But it is incorrect according to PCSpim and I should get

$3 := 0x1001_8010  

我感到困惑，为什么我需要对扩展addiu进行签名，据我了解，如果我执行addiu $1, $1, -10之类的操作，则应将其视为addiu $1, $1, 10，因为它是未签名的.

I am confused why I need to sign extend addiu, from what I understand if I do something like addiu $1, $1, -10 it should be treated as addiu $1, $1, 10 because it is unsigned.

那么为什么说我应该对立即数进行符号扩展?

So why does it say I should sign-extend the immediate value?

推荐答案

在spim中，

addiu    $3,$3,0x8010

是伪操作，并且由于addiu 指令不能[通过0x]被识别为对 unsigned 的渴望.因为符号扩展名].

is a pseudo-op and recognized as a desire for unsigned addition [by virtue of the 0x] which the addiu instruction can't do [because of the sign extension].

因此，spim生成:

ori    $1,$0,0x8010
addu   $3,$3,$1

在mars中，顺序为:

lui    $1,0
ori    $1,$1,0x8010
addu   $3,$3,$1

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