金星RISC-V如何循环，比较和打印? [英] Venus RISC-V how to loop, compare, and print?

问题描述

我正在尝试遍历数组，如果数字大于X，则打印.

I am trying to loop through an array and if the number is larger than X then print.

我试图在线查找教程，但是我只是停留在为什么它不起作用/没有输出任何东西的问题上.我的评论有点解释我的尝试.

I've tried to find tutorials online but I'm just stuck on why it is not working/outputting anything. My comments kind of explain what i tried to do.

.data
arrayOfNums:
.word 0
.word 1
.word 122
.word 1112
.word 4294967295
.word 22
.word 234234
.word 23332
.word 42
.word 23423

K: .word 2237

.text
.globl main

main:
####   *** vv My problem starts here vv ***   ####
la t0 K             #set t0 to K
la t1 arrayOfNums   #set t1 pointer to array
addi a1 t0 0        #add t0 deallocated to a1
addi a2 t1 0        #add t1 deallocated to a2

loop: 
    addi a0 x0 1        # print_int ecall
    addi a1 t1 0        # add t1 value to print
    ecall
    addi t1, t1, 4      # Increments t1 to move to the next element
    jal x0, loop

exit:
####Exit using environmental calls####
addi a1 x0 0         # random exit 0 
addi a0 x0 17        # print_int ecall
ecall

谢谢！

推荐答案

您发布的代码存在一些问题.

There are some issues with the code you have posted.

我正在尝试遍历数组，如果数字大于X，则打印.

I am trying to loop through an array and if the number is larger than X then print.

我在您的代码中找不到任何X符号.你是说K吗?

I can't find any X symbol in your code. Do you mean K?

la t0 K             #set t0 to K

该评论是错误的.您将K的地址加载到t0中.如果要将存储在该地址的值保存到t0中，则必须将该地址加载到另一个寄存器中，然后将该地址取消引用到t0中，即用lw或lwu指令加载它./p>

The comment is wrong. You load the address of K into t0. If you want to get the value that is stored at that address into t0 you have to load the address into another register and dereference that address into t0, i.e. load it with the lw or lwu instruction.

addi a1 t0 0        #add t0 deallocated to a1
addi a2 t1 0        #add t1 deallocated to a2

分配给"是什么意思?您将t0复制到a1，并且将t1复制到a2.可以使用mv伪指令归档相同的内容.但是，当您立即覆盖下面几行中的a1和a2寄存器时，这两行是多余的.

What do you mean with 'deallocated to'? You copy t0 to a1 and t1 to a2. The same could be archieved with the mv pseudo instruction. However, those 2 lines are superfluous as you immediately overwrite the a1 and a2 registers in the following lines.

    addi a0 x0 1        # print_int ecall
    addi a1 t1 0        # add t1 value to print
    ecall

您可以在此处使用li/mv伪指令.这将无条件打印t1的值-这是一个地址.如果要打印实际的数组元素，则必须使用t1-cf中存储的地址加载它. lw/lwu说明.

You could use the li/mv pseudo instructions here. This unconditionally prints the value of t1 - which is an address. If you want to print an actual array element you would have to load it using the address stored in t1 - cf. the lw/lwu instructions.

addi t1, t1, 4      # Increments t1 to move to the next element
jal x0, loop

这样一来，您将无条件跳到循环的开头(使用伪指令:j loop)，即，这意味着您读取了数组的末尾，并且永不退出循环.要解决此问题，您必须使用条件分支指令，例如bnez.意思是你将一个寄存器(作为计数器)设置为数组大小，并将其递减至零.或者将寄存器设置为最后一个数组元素之后的地址并分支，直到t1等于它.

With that you unconditionally jump to the head of the loop (with pseudo instruction: j loop), i.e. that means that you read over the end of your array and never quit the loop. To fix this you have to use a conditional branch instruction such as bnez. Meaning that you e.g. set a register (as counter) to the array size and decrement it until zero. Or set a register to the address after the last array element and branch until t1 is equal to it.

addi a1 x0 0         # random exit 0 
addi a0 x0 17        # print_int ecall
ecall

除了随机之外什么都没有.注释不正确，您正在调用Venus exit2系统调用，而不是print_int.此外，Venus还提供了不需要参数的退出系统调用(10).

It's anything but random. The comment is incorrect, you are calling the Venus exit2 syscall, not print_int. Besides, Venus also provides an exit syscall (10) that doesn't require an argument.

您的代码中完全缺少的是实际尝试比较数字，然后根据该比较结果打印它们的位置.

What is completely missing from your code is a location where you are actually trying to compare numbers and then print them based on that comparison.

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