Bit re-mapping / re-arranging

Page last updated 03 Jan 2011, by Dev Joshi. 0 replies

SPI write actually supports any number of bits in the format.

see for http://mbed.org/forum/mbed/topic/1630/ for ref to my original query.

For my own sake, here is some hashing out for a remapping routine, might come in useful at some point or another.

#include "mbed.h"

short InputArray [23]; //24 elements
char OutputArray [35]; //3 elements


char swapnibbles(char myChar) {
    char swapped = ((myChar >> 4) & 0x0f) | ((myChar << 4) & 0xf0);
    return swapped;
}

///can these be refactored in to a single routine which accepts 
//input value
//number of bits to mask (as a value)
//offset (to push to maskup or down against the value)
//and still return a byte
//use the offset to calculate how much to push resulting masked off section back down to fit into a char?     

char botnibble(short Input) {
    char OutputByte = 0;
    short BitMask = 0x000F; //Mask off the bottom nibble only
    short Temp = 0;
    Temp = (Input & BitMask); //Logical AND Mask and Input to get the lower nibble only
    OutputByte = OutputByte + Temp;
    return OutputByte;
}


char midnibble(short Input) {
    char OutputByte = 0;
    short BitMask = 0x00F0; //Mask off the middle nibble only
    short Temp = 0;
    Temp = (Input & BitMask); //Logical AND Mask and Input to get the lower nibble only
    OutputByte = OutputByte + (Temp >> 4); //shift all the bits in the result right 4 places such that value is in the bottom of the byte
    return OutputByte;
}

char topnibble(short Input) {
    char OutputByte = 0;
    short BitMask = 0x0F00; //Mask off the top nibble only
    short Temp = 0;
    Temp = (Input & BitMask); //Logical AND Mask and Input to get the lower nibble only
    OutputByte = OutputByte + (Temp >> 8); //shift all the bits in the result right 8 places such that value is in the bottom of the byte
    return OutputByte;
}

main() {

    int i = 0 ;
    char a,b,c,d,e,f = 0;


    for (i=0; i<=23;i++) {
        a = botnibble(InputArray[(2*i)]);
        b = midnibble(InputArray[(2*i)]);
        c = topnibble(InputArray[(2*i)]);
        d = botnibble(InputArray[((2*i)+1)]);
        e = midnibble(InputArray[((2*i)+1)]);
        f = topnibble(InputArray[((2*i)+1)]);
        OutputArray[(3*i)] = a + swapnibbles(b);
        OutputArray[((3*i)+1)] = c + swapnibbles(d);
        OutputArray[((3*i)+2)] = e + swapnibbles(f);
    };


}

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