jump.s

wARM兼容ARM7TDMI指令集

        AREA    Jump, CODE, READONLY    ; name this block of code

num     EQU     2                       ; Number of entries in jump table

        ENTRY                           ; mark the first instruction to call

start
        MOV     r0, #0                  ; set up the three parameters
        MOV     r1, #3
        MOV     r2, #2
        BL      arithfunc               ; call the function

stop
        MOV     r0, #0x18               ; angel_SWIreason_ReportException
        LDR     r1, =0x20026            ; ADP_Stopped_ApplicationExit
        SWI     0x123456                ; Angel semihosting ARM SWI

arithfunc                               ; label the function
        CMP     r0, #num                ; Treat function code as unsigned integer
        BHS     DoAdd                   ; If code is >=2 then do operation 0.

        ADR     r3, JumpTable           ; Load address of jump table
        LDR     pc, [r3,r0,LSL#2]       ; Jump to the appropriate routine

JumpTable
        DCD     DoAdd
        DCD     DoSub

DoAdd
        ADD     r0, r1, r2              ; Operation 0, >1
        MOV     pc, lr                  ; Return

DoSub
        SUB     r0, r1, r2              ; Operation 1
        MOV     pc,lr                   ; Return

        END                             ; mark the end of this file