MIPS-阵列中的阵列索引 [英] MIPS - Array in array index

问题描述

MIPS中的以下C代码是什么?

What is the following C code in MIPS?

f = A[B[i]]

有人告诉我它可以用6行完成，但还不知道怎么做. f 位于 $ t0 中， i 位于 $ t3 中， A [] 在 $ s0 中，而 B [] 在 $ s1 中.所有类型都是整数.

I'm told it can be done in 6 lines but can't quite figure out how. f is in $t0, i is in $t3, A[] is in $s0, and B[] is in $s1. All types are integer.

我能想到的最好的是

lw $t5, $t3($s0);  # Doesn't work because lw syntax doesn't accept a register as an offset
lw $t6, $t5($s1);
sadd $t0, $t6, $zero

显然这是错误的.我将如何获得每行的正确偏移量?

Obviously this is wrong. How would i go about getting the correct offset for each line?

谢谢.

推荐答案

可能有更有效的方法，但这是6行中的一种方法:

There might be more efficient ways, but here's one way in 6 lines:

sll $t2,$t3,2    # t2 = i * sizeof(int)
addu $t2,$t2,$s1 # t2 = &B[i]
lw $t0,0($t2)    # t0 = B[i]
sll $t0,$t0,2    # t0 *= sizeof(int)
addu $s0,$s0,$t0 # s0 = &A[B[i]]
lw $t0,0($s0)    # t0 = A[B[i]]

阅读 MIPS指令集参考以获得有关各个说明的详细信息.

Read a MIPS instruction set reference to get more information about what individual instructions do.

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