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LP-MSP430FR2476: uint left shift multiply truncating

Priya Nadathur
Intellectual 545 points
Part Number: LP-MSP430FR2476

I am trying to implement a multiplication with a scale factor. I am not seeing correct results in CCS. Is this type of multiplication possible to do?

uint16_t scaleFactorMult(uint16_t data){
uint64_t cellVolt = 0;
uint16_t channelVolt;
uint64_t xTwo12 = 0;
uint64_t xTwo9 = 0;
uint64_t xTwo7 = 0;
uint64_t xTwo5 = 0;

xTwo12 |= data << 12u;
xTwo9 |= data << 9u;
xTwo7 |= data << 7u;
xTwo5 |= data << 5u;
cellVolt |= xTwo12;
cellVolt |= xTwo9;
cellVolt |= xTwo7;
cellVolt |= xTwo5;

}

  • +1
    Guru 22685 points

    You are shifting a 16 bit integer and the result will always be 16 bits. If you what you want is a 64 bit result, you have to coerce the 16 bit integer into a 64 bit integer before shifting it. That is the way C has always worked. For example:

    Fullscreen
    1
    xTwo12 |= (uint64_t)data << 12u;
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

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