体系结构实验-DLX指令集-输入

体系结构实验-DLX指令集-输入-伪汇编

;*********** WINDLX Ex.1: Read a positive integer number*************

;-----------------------------------------------------------------------------

;Subprogram call by symbol "InputUnsigned"

;expect the address of a zero-terminated prompt string inR1

;returns the read value in R1

;changes the contents of registers R1,R13,R14

;-----------------------------------------------------------------------------

.data

;*** Data for Read-Trap

ReadBuffer: .space 80

ReadPar: .word 0,ReadBuffer,80

;*** Data for Printf-Trap

PrintfPar: .space 4

SaveR2: .space 4

SaveR3: .space 4

SaveR4: .space 4

SaveR5: .space 4

.text

.global InputUnsigned

InputUnsigned:

;*** save register contents；（sw:存储字）

sw SaveR2,r2

sw SaveR3,r3

sw SaveR4,r4

sw SaveR5,r5

;*** Prompt

sw PrintfPar,r1

addi r14,r0,PrintfPar ；r14=r1

trap 5

;*** call Trap-3 to read line

addi r14,r0,ReadPar ；r14=ReadPar

trap 3

;*** determine value确定值

addi r2,r0,ReadBuffer ；r2=ReadBuffer

addi r1,r0,0 ；r1清零

addi r4,r0,10         ; Decimalsystem

Loop: ;*** reads digits to end of line

lbu r3,0(r2) ；加载

seqi r5,r3,10 ;LF -> Exit

subi r3,r3,48

              bnez r5,Finish

multu r1,r1,r4 ;Shift decimal改变小数

add r1,r1,r3

addi r2,r2,1 ;increment pointer增加指针

j Loop

Finish: ; restore old register contents

lw r2,SaveR2

lw r3,SaveR3

lw r4,SaveR4

lw r5,SaveR5

jr r31 ; Return