.org 0x0
 	.global _start
_start:
    addi  zero, zero, 0x123
    addi  zero, zero, 0x456
    
    lui   sp, 0x00010
    ori   sp, sp, 0x400 # stack pointer=0x400, stack size = 256 dwords
    
    xori  t0, zero, 6   # t0 = 6
    jal   ra, fibonacci_recursive
    
    xori  a1, t1,   0   # 计算完成，结果在t1中，闲着没事干把它放到a1里好了
    jal   zero, program_end # 跳到死循环程序

fibonacci_recursive:    # 递归计算斐波那契数列的第n项，
                        # n放在t0寄存器中
                        # 结果放在t1寄存器中
                        # 使用ra作为返回地址，并使用堆栈，堆栈指针为sp
    
    ori   a0, zero, 3   # a0 = 3
    bgeu  t0, a0, tag   # if t0>=a0(3), jmp to tag
    ori   t1, t0,   0   # t1 = t0
    jalr  zero, ra, 0   # pc = ra
    
tag:
    addi  sp, sp, -4    # sp-=4        # push ra to stack
    sw    ra, (sp)      # mem[sp] = ra
    
    addi  t0, t0, -1    # t0-=1
    addi  sp, sp, -4    # sp-=4        # push t0 to stack
    sw    t0, (sp)      # mem[sp] = t0
    
    jal   ra, fibonacci_recursive      # fibonacci_recursive n-1
    
    lw    t0, 0(sp)     # t0=mem[sp]   # pop t0 from stack
    addi  sp, sp,  4    # sp+=4
    addi  t0, t0, -1    # t0-=1
    
    addi  sp, sp, -4    # sp-=4        # push t1 to stack
    sw    t1, (sp)      # mem[sp] = t1
    jal   ra, fibonacci_recursive      # fibonacci_recursive n-2
    lw    t2, 0(sp)     # ra=mem[sp]   # pop t2 from stack
    addi  sp, sp,  4    # sp+=4
    add   t1, t1, t2    # t1+=t2
    
    lw    ra, 0(sp)     # ra=mem[sp]   # pop ra from stack
    addi  sp, sp,  4    # sp+=4
    
    jalr  zero, ra,0    # pc = ra
    
program_end:
    jal   zero, program_end # infinity loop