My math

myMath.h

/*
    Macro to convert the MSB/LSB of a 16-bit value to a 8-bit value
*/
#define GET_16BIT_MSB( x )        ( (uint8_t)( ( ( (uint16_t)(x) ) >> 8 ) & 0xFF ) )
#define GET_16BIT_LSB( x )        ( (uint8_t)(   ( (uint16_t)(x) )        & 0xFF ) )

/* macro to write the 16-bit value into an 8-bit buffer */
#define BUF_SET_16BIT( buf, value )                   \
    do {                                                        \
        ((uint8_t *)(buf))[ 0 ] = GET_16BIT_MSB(value); \
        ((uint8_t *)(buf))[ 1 ] = GET_16BIT_LSB(value); \
    } while ( 0 )
    
/* macro to read a 16-bit value from an 8-bit buffer */    
#define BUF_GET_16BIT( buf )                          \
    ( ( ((uint16_t)( ((uint8_t *)(buf))[ 0 ] ) ) << 8   )         \
    | ( ((uint16_t)( ((uint8_t *)(buf))[ 1 ] ) ) & 0xFF )         \
    )

/*
    Convert an unsigned int to signed int.
*/
int16_t unsignedToSigned(uint16_t val)
{
    if(val > 0x8000)
         val = -((65535 - val) +1);
    return val;
}

/*
    Check Prime number
*/
unsigned char isPrimeNumber(int n)
{
    if(n < 2) return 0;
    int temp = (int)sqrt(n);
    for(i = 2; i < temp; i++)
        if(n % i == 0) return 0;
    return 1;
}

/*
    Find Greatest Common Divisor - GCD
*/
int GCD(int a, int b)
{
    while(b != 0)
    {
        int temp = a % b;
        a = b; b = temp;
    }
    return b;
}

unsigned short u16ToLittleEndian( unsigned short u16input )
{/* Use this function to convert a 16-bit number into little endian. */

  return( (u16input >> 8) ^ (u16input << 8) );

}// end u16ToLittleEndian()

unsigned long u32ToLittleEndian( unsigned long u32input )
{/* Use this function to convert a 32-bit number into little endian. */

  return( (u32input >> 24)
           ^ ( (u32input >> 8) & 0x000FF00 )
           ^ ( (u32input << 8) & 0x00FF0000 )
           ^ ( (u32input << 24) & 0xFF000000 )
         );

}// end u32ToLittleEndian()