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C51 - Calculating the parity

Chris s

Has someone a good hint how to implement a parity-calculation of a byte in the most efficient way on an C51-device?

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  • 0 in reply to Jonny Doin

    Another use of the comma operator: you can get the 16bit result from the multiplication of 2 unsigned char without any call to the math clib:

        unsigned char data a, b;
    unsigned int data x;

    a = 36;
    b = 130;

    // this is 400% faster than a x = (unsigned int) a * b
    *(unsigned char*)&x = ((((unsigned char*)&x)[1] = a * b), B);

    I am just too lazy: you can make the int variable a union to access the msb and lsb parts, to improve readability, but the generated code is the same: 11 instruction cycles against 40 cycles using a 16bit cast.

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  • 0 in reply to Jonny Doin

    Another use of the comma operator: you can get the 16bit result from the multiplication of 2 unsigned char without any call to the math clib:

        unsigned char data a, b;
    unsigned int data x;

    a = 36;
    b = 130;

    // this is 400% faster than a x = (unsigned int) a * b
    *(unsigned char*)&x = ((((unsigned char*)&x)[1] = a * b), B);

    I am just too lazy: you can make the int variable a union to access the msb and lsb parts, to improve readability, but the generated code is the same: 11 instruction cycles against 40 cycles using a 16bit cast.

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