ARM number conversion program

Question

I am trying to write a program that will convert a number from ieee to TNS (big endian), and vice versa. I\'m very new to ARM and assembly in general. I\'m not getting an erro

Answer 1

I think I know understand what you are trying to achieve.

I wrote up a program that uses the decimal number 15.75.
This number is stored in IEEE754 format.
It is first converted to TNS format the converted number is printed to the console. The number is then converted back to IEEE745 format. The converted number is printed to the console then the program exits.

This program is written for ARM7.

Take a look at the code if it sounds like that is what you are trying to achieve:

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