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Integer overflow

Hello to everyone.

When I have to calculate the average of two integer numbers, first i have to add them. Sometimes an overflow occurs. One technique maybe to compare the result to one of the numbers, if result is lower, an overflow is recognized.

Is this good style or better use Assembler?

Parents

0 Dieter Coba over 19 years ago in reply to Dieter Coba

Here's the corrected version, divided into average for signed / unsigned numbers.

//*********************************************************************
// Computing the average of Signed numbers in ARM Assembler
//*********************************************************************
AREA ?C?bla, CODE, READONLY, ALIGN=2

PUBLIC          my_signed_average?A
                        my_signed_average?A             PROC CODE32

        ADDS    R0,R0,R1                ;add and alter condition code
        MOVVS   R0,R0,RRX               ;if sign has moved to C rotate through Carry
        MOVVC   R0,R0,ASR #1    ;if sign not changed do arithmetic shift
        bx              lr                              ;return R0
        ENDP
//*********************************************************************
// Computing the average of Unsigned numbers in ARM Assembler
//*********************************************************************
PUBLIC          my_unsigned_average?A
                        my_unsigned_average?A   PROC CODE32

        ADDS    R0,R0,R1                ;add and alter condition code
        MOV             R0,R0,RRX               ;rotate through Carry
        bx              lr                              ;return R0
        ENDP

        END
//*********************************************************************

Reply

0 Dieter Coba over 19 years ago in reply to Dieter Coba

Here's the corrected version, divided into average for signed / unsigned numbers.

//*********************************************************************
// Computing the average of Signed numbers in ARM Assembler
//*********************************************************************
AREA ?C?bla, CODE, READONLY, ALIGN=2

PUBLIC          my_signed_average?A
                        my_signed_average?A             PROC CODE32

        ADDS    R0,R0,R1                ;add and alter condition code
        MOVVS   R0,R0,RRX               ;if sign has moved to C rotate through Carry
        MOVVC   R0,R0,ASR #1    ;if sign not changed do arithmetic shift
        bx              lr                              ;return R0
        ENDP
//*********************************************************************
// Computing the average of Unsigned numbers in ARM Assembler
//*********************************************************************
PUBLIC          my_unsigned_average?A
                        my_unsigned_average?A   PROC CODE32

        ADDS    R0,R0,R1                ;add and alter condition code
        MOV             R0,R0,RRX               ;rotate through Carry
        bx              lr                              ;return R0
        ENDP

        END
//*********************************************************************

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