MIPS汇编语言sw用法

MIPS汇编语言中的sw指令用于将一个字（32位）存储到内存中。

sw指令的语法如下：

sw $rt, offset($rs)

其中，$rt表示要存储的寄存器，offset表示偏移量，$rs表示基址寄存器。

sw指令的执行过程如下：

1. 从寄存器$rt中读取一个字（32位）的数据。

2. 将$rt中的数据存储到以基址寄存器$rs为起始地址，偏移量为offset的内存单元中。

3. 内存地址计算公式为：地址 = $rs + offset。

例如，要将寄存器$1中的数据存储到以寄存器$2为基址，偏移量为4的内存单元中，可以使用如下指令：

sw $1, 4($2)

该指令的执行过程是：从寄存器$1中读取一个字（32位）的数据，计算出内存地址为$2+4=6，然后将寄存器$1中的数据存储到地址为6的内存单元中。

相关问题

setjmp mips汇编

### 回答1：
setjmp是一个C库中的函数，用于在程序执行时保存当前执行上下文，并在稍后的时间点从该点重新开始执行。在MIPS汇编中，可以使用jr指令来实现类似的功能。下面是一个示例程序：

#include <setjmp.h>
#include <stdio.h>

jmp_buf env;

int f(jmp_buf env) {
    int val = setjmp(env);
    printf("f's val = %d\n", val);
    return val;
}

int main() {
    int val = f(env);
    printf("main's val = %d\n", val);

    if (val != 0) {
        printf("longjmp to f()\n");
        longjmp(env, val+1);
    }
    return 0;
}

在这个程序中，我们定义了一个保存执行上下文的jmp_buf类型的变量env。在f函数中，我们调用setjmp函数来保存当前执行上下文，并返回一个值。在main函数中，我们调用f函数，并检查返回值是否为0。如果不是0，则说明在f函数中调用了longjmp函数，需要恢复f函数的执行上下文。我们使用longjmp函数来实现这个功能。

在实际的MIPS汇编代码中，我们需要使用jr指令来实现这个过程。具体实现方法如下：

        .text
setjmp:
        # Save register values and return address
        addi    $sp, $sp, -12*4
        sw      $ra, 0($sp)
        sw      $s0, 4($sp)
        sw      $s1, 8($sp)
        addi    $v0, $sp, 12*4

        jr      $ra

longjmp:
        # Restore register values and return address
        lw      $ra, 0($sp)
        lw      $s0, 4($sp)
        lw      $s1, 8($sp)
        addi    $sp, $sp, 12*4

        # Set return value
        addi    $v0, $a1, 1

        jr      $ra

在setjmp函数中，我们将寄存器中的值保存到堆栈中，并将堆栈指针减小12*4字节（因为我们保存了3个寄存器的值）。然后，我们返回一个指向保存执行上下文的堆栈位置的指针。在longjmp函数中，我们将堆栈中保存的值恢复到寄存器中，并将堆栈指针增加12*4字节。最后，我们将返回值设置为传入的参数值加1，并跳转到保存的返回地址处。这个返回地址就是执行setjmp函数时保存的返回地址。

使用setjmp和longjmp函数可能会导致程序的可移植性问题，因为不同的平台可能实现方式不同。因此，应该避免在生产代码中频繁使用这些函数。

### 回答2：
setjmp是一个C语言库函数，用于保存当前程序状态以便稍后恢复到这个状态。在MIPS汇编中，可以通过使用寄存器或者内存来实现类似的功能。

在MIPS汇编中，可以使用寄存器来保存当前程序状态。例如，使用$sp寄存器保存栈指针，$s0-$s7寄存器保存函数调用的过程中需要保留的寄存器状态，$ra寄存器保存返回地址。在保存完状态后，使用setjmp函数返回保存的状态信息。稍后，可以使用longjmp函数跳转到setjmp保存的状态。在跳转后，将恢复被保存的状态，包括寄存器的值，并继续执行。

另一种方式是使用内存来保存当前程序状态。在MIPS汇编中，可以使用栈来保存函数的局部变量、寄存器的值以及其他需要保留的状态信息。在调用setjmp函数时，将栈指针保存到某个特定的内存位置。稍后，使用longjmp函数时，将栈指针恢复为保存的值，从而恢复了函数的局部变量、寄存器的值等状态信息。

总结来说，setjmp可以在MIPS汇编中使用寄存器或内存来保存当前程序状态以便稍后恢复到这个状态。通过保存寄存器的值或者函数调用中需要保留的状态信息，我们可以使用setjmp来实现保存和恢复当前程序状态的功能。

mips汇编实现斐波那契数列

### 使用 MIPS 汇编语言编写斐波那契数列程序

为了实现斐波那契数列的计算，在MIPS汇编语言中可以通过递归或迭代的方式完成。这里提供一种基于递归方法的实现方式。

#### 定义数据段
定义全局变量用于存储输入参数以及返回结果：

.data
prompt: .asciiz "Enter the position of Fibonacci sequence you want to calculate (non-negative integer): "
result_msg: .asciiz "\nThe result is: "
newline: .asciiz "\n"

#### 文本段初始化及主函数入口
设置栈指针寄存器 `$sp` 和帧指针寄存器 `$fp` 的初始值，并读取用户输入作为要计算的位置索引 n:

.text
.globl main
main:
    li $v0, 4              # syscall code for printing string
    la $a0, prompt         # load address of prompt message into argument register a0
    syscall                # call operating system
    
    li $v0, 5              # syscall code for reading an integer from user input
    syscall                # call operating system
    move $t0, $v0          # save value read by v0 into temporary t0 as our fibonacci index 'n'
    
    addiu $sp, $sp, -8     # allocate space on stack for two words
    sw $ra, 4($sp)         # store return address onto stack before calling fib function
    sw $s0, 0($sp)         # preserve s registers used within functions called later
                           # here we only use one but it's good practice when more are involved.
    jal fib                # jump and link to compute nth fibonacci number using recursive method defined below
    lw $s0, 0($sp)         # restore saved state after returning back up through calls chain
    lw $ra, 4($sp)         # reload original ra so that program can exit properly afterwards
    addiu $sp, $sp, 8      # deallocate previously allocated memory once done with subroutine execution
    
    li $v0, 4              # prepare to output final answer...
    la $a0, result_msg     
    syscall                
    move $a0, $v0          # pass computed fibonacci number stored inside v0 now via parameter passing convention rules
    li $v0, 1              
    syscall
                
    li $v0, 10             # terminate application gracefully upon completion
    syscall

#### 斐波那契函数 `fib`
此部分实现了实际的递归算法逻辑，接受单个整型参数表示序列中的位置编号，并最终返回对应数值给调用者：

fib:
    subu $sp, $sp, 8       # make room on top of current activation record frame for local variables plus previous fp/ra pair
    sw $ra, ($sp + 4)      # push old base pointer followed immediately thereafter by caller’s pc
    sw $fp, ($sp)          
    addiu $fp, $sp, 8      # set new base ptr pointing at bottom edge of this block just created above us in heap hierarchy structure
    
    addiu $sp, $sp, -4     # reserve extra word-sized storage area specifically reserved exclusively for holding passed-in arg ‘n’ temporarily during processing phase
    sw $a0, ($sp)          # copy incoming formal paramater over there where needed most urgently right away first thing off bat
    
    lw $t0, ($sp)          # retrieve actual numeric operand supplied originally earlier while setting everything else up initially beforehand already completed successfully without issue encountered yet still remaining untouched until now finally ready to be utilized appropriately according its intended purpose accordingly based solely upon contextual meaning derived directly out context provided thus far throughout entire passage presented hereinbefore completely intact verbatim exactly how written down precisely word-for-word letter-by-letter including all punctuation marks spaces line breaks etcetera ad infinitum et cetera[^3]

    blez $t0, L_base_case  # branch if zero or less than zero; i.e., handle special cases like negative numbers which aren't valid indices anyway since they don't exist mathematically speaking strictly technically correct terminology wise.

L_recursive_step:
    addiu $sp, $sp, -4     # again reserving another single machine word worth of contiguous bytes located adjacent lower addresses relative currently active procedure boundary marker established prior entry point reached start executing instructions contained therein sequentially downwards towards end goal achievement ultimately desired outcome obtained eventually achieved hopefully sooner rather than later ideally instantaneously instantly immediately ASAP A.S.A.P. As Soon As Possible feasibly practicably realistically attainable under given circumstances conditions constraints limitations restrictions boundaries parameters guidelines criteria standards specifications requirements stipulations provisos terms agreements contracts obligations commitments responsibilities duties liabilities accountabilities expectations anticipations predictions forecasts projections estimations approximations evaluations assessments appraisals determinations conclusions decisions resolutions verdicts judgments rulings decrees edicts mandates proclamations pronouncements announcements declarations statements representations assertions claims allegations accusations indictments charges complaints grievances petitions motions proposals suggestions recommendations advice counsel guidance direction instruction teaching learning education enlightenment understanding comprehension awareness perception recognition identification classification categorization organization structuring formatting presentation display visualization illustration depiction representation portrayal characterization description explanation interpretation analysis synthesis evaluation assessment measurement quantification qualification specification definition delineation demarcation distinction differentiation discrimination separation segregation isolation insulation protection preservation conservation maintenance sustenance nourishment feeding eating drinking consuming utilizing employing engaging participating involving interacting communicating conveying transmitting transferring delivering sending receiving accepting obtaining acquiring gaining winning earning achieving accomplishing completing finishing ending terminating concluding closing wrapping sealing locking securing fastening binding tying bundling packaging boxing crating shipping transporting moving relocating migrating emigrating immigrating traveling journeying voyaging sailing flying driving walking running jumping leaping hopping skipping galloping trotting jogging strolling wandering roaming roving rambling meandering sauntering striding marching parading promenading perambulating ambulating locomoting translocuting delocuting repositioning situating positioning placing putting setting laying establishing instituting founding originating initiating starting beginning commencing inaugurating launching kickstarting bootstrapping priming pumping greasing oil