ARMv7 程序集，我该如何改进这个伪随机数生成器？

Question

我有这个伪随机函数，它基于自 unix epotch 作为种子以来的时间，我需要得到 1-5 之间的 4 个数字，目前我所做的是一次获取一个数字并打印它。这最初是针对 0-9 之间的数字并将其更改为 1-5 我意识到数字 6-9 将始终导致为 5，这意味着 5 比任何其他数字具有更高的总体出现概率。

这只是一个简单的猜谜游戏，所以它没有做任何事情

timeofday:

    MOV r7, #78         @gettimeofday returns time
    LDR r0, =time       @address of holder for time_t
    MOV r1, #0          @timezone not needed
    SWI #0
    
    LDR r0, =time       @set r0 back to label addr
    LDRB r1, [r0, #4]   @load epotch value from r0 into r1
    
    MOV PC, LR          @back to calling location, Then it will branch to the function below.

fakemod:
    CMP r1, #10         @Ensuring we don't create a negative
    SUBGE r1, r1, #10   @decrease r1 by 10 until it's a single digit
    CMP r1, #10
    BGE fakemod         @if the number in r1 is still greater than 10 loop
    
singledigit:            @Need a value between 1-5
    CMP r1, #5          @Checks in r1 has a value larger than 5
    SUBGT r1, r1, #1    @subtracts if r1 is a integer greater than 5
    CMP r1, #5          @compares if the number is greater than 5 still
    BGT singledigit     @if greater than 5 go back to loop start.
    
    CMP r1, #0       @needs to be between 1-5, so if it's 0, just add 1
    ADDEQ r1, r1, #1
     
    MOV PC, LR          @once it's an integer between 1-5, go back to call location. 

我没有连续从大于 5 的值中减去 1 并将 1 加到 0 的值上，而是尝试了以下操作，得到了“垃圾”作为输出：

timeofday and fakemod loop are the same.

CMP r1, #5
BGT timeofday

CMP r1, #0
BEQ timeofday

Answer 1

我将 fakemod 函数更改为以下，并得到了我理想中想要的结果。在随机数生成器中将 1 添加到 0 并不理想，但它足以满足我的需求。几周前写的，所以我有点忘记了目的。

fakemod:
    CMP r1, #5       @Ensuring we don't create a negative
    SUBGT r1, r1, #5 @decrease r1 by 5 until it's a single digit
    CMP r1, #5
    BGT fakemod         @if the number in r1 is still greater than 10 loop

    CMP r1, #0
    ADDEQ r1, r1, #1

    MOV PC, LR          @once it's an integer less than 5, go to top.