# Lab1: RV32I Simulator
###### tags: `Computer Architecture 2021`
## Single number
This problem is based on [LeetCode 344](https://leetcode.com/problems/reverse-string/). Write a function that reverses a string. The input string is given as an array of characters s

## C Code

void reverseString(char* s, int sSize){
    char tem;
    for(int i=0;i<=sSize/2-1;i++)
    {
        tem=s[i];
        s[i]=s[sSize-i-1];
        s[sSize-i-1]=tem;
        
    }
    
}

## Assembly code
### 1.use address

#use address
.data
arr: .word 104,101,108,108,111 #hello in AscII
space: .string " "
len: .word 5
.text
main:
    
    la s1,arr     #load the array
    lw s2, len    #load the length of array
    li s5,4       #define the unit offset
    mul s6,s2,s5  #get the size of byte of array
    sub,s6,s6,s5  #get the end of array address
    add,s1,s6,s1  #get the address of last item of array
    jal ra, loop1 #jump to loop1
    ecall
loop1:
    addi t0,t0,1  #i++
    lw a0, (0)s1  #get the item at the address
    li a7,1       #print the item
    ecall
    la a0,space
    li a7,4       #print space
    ecall
    sub s1,s1,s5  #get the pre address of array
    blt t0,s2,loop1 #if i<len jump to loop
 

### 2.two arrays

.data
arr: .word  104,101,108,108,111 #hello in AscII
arr2: .word 11,12,12,16,17,15 #nums[5]={1,2,3,4,5}

len: .word 6
.text
main:
    la s1,arr
    la s7,arr2
    lw s2, len
    li s5,4
    mul s6,s2,s5
    sub,s6,s6,s5
    add,s1,s6,s1
    jal ra, loop1
   
    jal ra, out
    ecall
loop1: 
    addi t0,t0,1
    lw a0,0(s1)
    add t2,a0,x0
    lw a0,0(s7)
    sw a0,0(s1)
    add a0,t2,x0
    sw a0,0(s7)
    
    add s7,s7,s5
    
    sub s1,s1,s5
    blt t0,s2,loop1
out:
  
    
    sub s7,s7,s6
    sub s7,s7,s5
    loop2:
        addi t1,t1,1
        lw a0, (0)s7
        add s7,s7,s5
    
        li a7,1
        ecall
    
        blt t1,s2,loop2
    
    

### 3.One array

.data
arr: .word  104,101,108,108,111 #hello in AscII
output: .string "  output is"
space: .string "  " 

len: .word 5
.text
main:
    la s1 arr
    lw s2, len
    li s5,4
    li s7,1
    li s8,2
    slli s8,s2,2 #max end address gap
    sub,s8,s8,s5 #max end item address gap
    jal ra, reverse
    jal ra, out
    ecall
    
reverse: 
   div s9,s8,s2   #size/2
   sub s9,s9,s7   #size/2-1

    loop1:
        
        addi t0,t0,1   #i++
        sub t3,t0,s7   #i-1
        add t4,t3,t3   #2(i-1)
        slli t4,t4,2   #2(i-1)*4(bytes)
        sub t6,s8,t4   #gap for exchange item
        lw a0,0(s1)    
        add t2,a0,x0   #temp=x[i]
        add,s1,t6,s1   #x[max-i]
        lw a0,0(s1)    #a0=x[max-i]
        sub s1,s1,t6   #x[i]
        sw a0,0(s1)    #x[i]=a0
        add s1,s1,t6   #x[max-i]
        add a0,t2,x0   
        sw a0,0(s1)    #x[max-i]=temp
        sub s1,s1,t6   #x[i]
        add s1,s1,s5   #x[i+1]
        
        blt t0,s9,loop1 #if i<(size/2-1) jump to loop
        
out:
    la a0 ,output
    li a7,4
    slli s10,t0,2      #get the final address gap of s1 in loop1
    sub s1,s1,s10      #minus offset
    ecall
    loop2:
        addi t1,t1,1   #i++
        lw a0, (0)s1   #a0=x[i]
        add s1,s1,s5   #x[i+1]
        li a7,1
        ecall
        la a0,space
        li a7,4
        ecall
    
        blt t1,s2,loop2 # if i<len go to loop2

## Pipeline feature in Ripes

## Hazard issue
I haven't found out how to initialize the start address of array

## Reference
[hrh47's computer organization note](https://hackmd.io/@8bFA57f7SRG-K7AAT8s62g/ryv1NT3S#%E7%AC%AC18%EF%BD%9E21%E8%AC%9B-Pipelining-75)