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我正在尝试编写一个程序，将数字从 ieee 转换为 TNS（大端），反之亦然。一般来说，我对 ARM 和汇编很陌生。我没有收到错误，它只是没有按预期工作，如果有人可以查看它，我将不胜感激。每一行都有注释，这里实际讨论的子程序是“unpack ieee”程序，它没有按预期工作，我不明白为什么。编辑：IEEE 和 TNS 号码有 3 个部分，我正在尝试使用掩码“抓取”或分离这 3 个部分。解包过程使用掩码将每个部分放入单独的寄存器中，以便我可以操作每个部分以进行转换。目前我正在尝试通过调用它来确认解包过程是否有效，然后打印寄存器。结束编辑我还没有编写转换例程，但是如果您愿意，我可以发布一个伪代码算法。如果您还有其他想知道的，请告诉我。编码：

AREA Conversion, CODE
SWI_WriteC  EQU &0          ;output character in r0 
SWI_WriteL  EQU &2          ;output String in r0
SWI_Exit    EQU &11         ;finish program
    ENTRY

    ADR r0, STRING  ;load string
    SWI SWI_WriteL  ;print string
    LDR r1, IEEE    ;load IEEE num into r0
    BL  Print       ;print number
    BL  UnpackIEEE  ;call UnpackIEEE subroutine
    ADR r1, r4      ;
    BL  Print
    SWI     SWI_Exit    ;finish

UnpackIEEE
    LDR r1, SMASK   ;load the sign bit mask into r1 
    LDR r2, EMASK   ;load the exponent mask into r2
    LDR r3, GMASK   ;load the significand mask into r3
    AND r4, r0, r1  ;apply sign mask to IEEE and save into r4
    AND r5, r0, r2  ;apply exponent mask to IEEE and save into r5
    AND r6, r0, r3  ;apply significand mask to IEEE and save into r6
    MOV     pc, r14     ;return

ConvToTNS


Print   MOV r2,#8       ;count of nibbles = 8
LOOP    MOV r0,r1,LSR #28   ;get top nibble
    CMP     r0, #9      ;hexanumber 0-9 or A-F
    ADDGT   r0,r0, #"A"-10  ;ASCII alphabetic
    ADDLE   r0,r0, #"0" ;ASCII numeric
    SWI     SWI_WriteC  ;print character
    MOV r1,r1,LSL #4    ;shift left one nibble
    SUBS    r2,r2, #1   ;decrement nibble count
    BNE LOOP        ;if more nibbles,loop back
    MOV     pc, r14     ;return


IEEE    DCD 0x40280000  ;2.75 or 40,280,000
TNS     DCD 0x28000101  ;2.75 or 28,000,101
SMASK   DCD 0x80000000  ;Sign bit mask
EMASK   DCD 0x7F800000  ;Exponent mask
GMASK   DCD     0x007FFFFF  ;Significand mask
STRING  DCB "HI THERE",0
    END
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1 回答 1

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我想我知道你想要达到的目标。

我编写了一个使用十进制数 15.75 的程序。
此编号以 IEEE754 格式存储。
它首先被转换为 TNS 格式，转换后的数字被打印到控制台。然后将数字转换回 IEEE745 格式。转换后的数字会打印到控制台，然后程序退出。

该程序是为 ARM7 编写的。

如果听起来这是您想要实现的目标，请查看代码：

ENTRY
        LDR r0, IEEE        ; Load IEEE formatted # into r0
        BL  ieeetotns       ; Branch to IEEE to TNS conversion subroutine
        BL  Print           ; Branch to print number to console
        BL  tnstoieee       ; Branch to TNS to IEEE conversion subroutine
        BL  Print           ; Branch to print number to console
        SWI     SWI_Exit    ; Exit Program

        ; Load IEEE Masks into registers
ieeetotns   LDR r1, SIGNMASK        ; Load sign mask into r1
            LDR r2, IEEEEXPMASK     ; Load IEEE exponent mask into r2
            LDR r3, IEEESIGMASK     ; Load IEEE significand mask into r3

            ; Convert from IEEE to TNS
            AND r4, r0, r1          ; unpack sign bit, store in R4
            AND r5, r2, r0          ; initial unpack of exponent, store in r5
            MOV r5, r5, LSR #23     ; shift exponent right 23 bits  
            ADD r5, r5, #129        ; add 129(10) to exponent to correct excess encoding for TNS
            AND r6, r3, r0          ; initial unpack of significand, store in r6
            ADD r6, r7, r6, LSL #8  ; shift significand left 8 bits, kill off LSB
            ORR r0, r4, r5          ; pack sign and exponent
            ORR r0, r0, r6          ; pack significand with sign and exponent, 
                                    ; r0 now holds IEEE to TNS converted word
            MOV PC, LR              ; Return to main subroutine 

        ; Load TNS Masks
tnstoieee   LDR r1, SIGNMASK        ; Load sign mask into r1
            LDR r2, TNSSIGMASK      ; Load TNS Significand mask into r2
            LDR r3, TNSEXPMASK      ; Load TNS Exponent mask into r3

        ; Convert back to IEEE
            AND r4, r0, r1          ; unpack sign bit
            AND r5, r2, r0          ; initial unpack of significand, store in r5
            MOV r5, r5, LSR #8      ; Shift significand right 8 bits
            AND r6, r3, r0          ; Initial unpack of exponent, store in r6
            SUB r6, r6, #129        ; Subtract 129 to correct excess encoding
            ADD r6, r7, r6, LSL #23 ; Shift exponent left 23 bits

        ; Pack the converted number into r0
            ORR r0, r4, r5          ; Pack sign and significand
            ORR r0, r0, r6          ; Pack exponent with sign and significand, 
                                    ; r0 now holds TNS to IEEE converted word
            MOV PC, LR              ; Return to main subroutine

Print       MOV r2, #8              ; Count of nibbles = 8
            MOV r1, r0              ; Move number to r1
            MOV r3, r0              ; Store converted number in r3 for later
LOOP        MOV r0, r1, LSR #28     ; Get top nibble
            CMP r0, #9              ; Hex number 0-9 or A-F?
            ADDGT   r0, r0, #"A"-10 ; ASCII A-F
            ADDLE   r0, r0, #"0"    ; ASCII 0-9
            SWI SWI_WriteC          ; Print character to console
            MOV r1, r1, LSL #4      ; Shift left one nibble
            SUBS    r2, r2, #1      ; Decrement nibble count
            BNE     LOOP            ; If more nibbles loop again
            MOV r0, #10             ; Load 10 into r0, ASCII code for carriage return
            SWI SWI_WriteC          ; Print carriage return to console
            MOV r0, r3              ; Move converted number back to r0
            MOV PC, LR              ; Return to main subroutine     


IEEE        DCW 0x0000, 0x417C  ; IEEE Representation of 15.75(10), 417C0000(16), 
                                ; 01000001011111000000000000000000(2)
TNS         DCW 0x0103, 0x7C00  ; TNS  Representation of 15.75(10), 7C000103(16), 
                                ; 01111100000000000000000100000011(2)
                                ; This is not used in program, simply here for comparison of conversions

SIGNMASK    DCW 0x0000, 0x8000  ; Mask for sign bit
IEEEEXPMASK DCW 0x0000, 0x7F80  ; Mask for IEEE Exponent
IEEESIGMASK DCW 0xFFFF, 0x007F  ; Mask for IEEE Significand
TNSSIGMASK  DCW 0xFE00, 0x7FFF  ; Mask for TNS Significand
TNSEXPMASK  DCW 0x01FF, 0x0000  ; Mask for TNS Exponent
END
于 2013-03-13T22:36:43.790 回答