MIPS实现Code 128解码器：数组读取整数异常问题求助

Hey Rozek, let's break down the problem you're facing—when reading array elements, $t4 isn't grabbing the expected 0x6CC for code_0, and incrementing $t5 by 4 makes $t4 increase by 4 instead of matching your actual array values. This almost always traces back to memory address mismanagement or incorrect array/instruction usage. Let's walk through the most likely fixes:

1. Double-Check How You're Loading the Array Base Address #

This is the most common culprit. In MIPS, to get your array's starting memory address, you need to use the la (load address) instruction—not lw (load word).

If you wrote something like this:

lw $t5, code_array  # WRONG! This loads the FIRST VALUE of code_array into $t5, not the address

Then $t5 will hold 0x6CC (your first element) instead of the actual array location. When you increment $t5 by 4, you're pointing to a random memory spot (0x6CC + 4 = 0x6D0) instead of the next array element. Reading from there will give unpredictable values that might coincidentally increase by 4 each time.

The correct way to load the array's base address is:

la $t5, code_array  # CORRECT! Loads the starting memory address of code_array into $t5

2. Verify Your Array Definition in the .data Section #

Make sure you're declaring your array with .word (since you're storing 32-bit integers). If you accidentally used .byte or .half, your elements won't be aligned as 4-byte words, leading to mangled values when you read with lw.

Correct array definition example:

.data
code_array: .word 0x6CC, 0xXXXX, 0xYYYY, ...  # Each element is a 4-byte integer

If you used .byte, each "element" would only take 1 byte, so lw $t4, ($t5) would read 4 consecutive bytes as a single word—completely breaking your intended Code 128 values.

3. Confirm You're Using the Right Load Instruction #

Since you're storing 32-bit integers, you must use lw (load word) to read elements. If you mistakenly used lb (load byte) or lh (load halfword), you'd only get a portion of the integer, and incrementing the address by 4 would skip 4 elements instead of moving to the next integer.

Correct read operation example:

lw $t4, ($t5)       # Reads the 4-byte integer at address $t5 into $t4
addi $t5, $t5, 4    # Moves to the next integer (4 bytes ahead)

4. Check for Address Alignment #

MIPS requires word-aligned memory accesses (addresses must be divisible by 4, ending in 00 in binary). If your array's base address isn't aligned, lw might cause exceptions or read incorrect data. Using la and .word should handle alignment automatically, but if you manually calculated the base address, double-check it's divisible by 4.

Start with verifying the la instruction first—it's the most frequent mistake here. Let me know if you still hit snags after checking these steps!

内容的提问来源于stack exchange，提问作者Rozek