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Initialize long with floats binary representation

Jürgen Breuer

Hello,

how can I achieve


long l = WHAT_EVER_MACRO (-12.5);

main()
{
  printf("%X",l);
}

resulting in output "0xC1480000" the binary representation of the float -12.5 .
Without that MACRO the value is 0xFFFFFFF4 = -12 for integers .

Because of given circumstances in an existing project I have to store float values during initialization in long variables.

Is there any possibility?

Thanks in advance

Jürgen

Parents
  • 0 in reply to Jürgen Breuer

    As I did write earlier, the floats will not take their binary representation until (not before) they are stored in memory.

    If the value is already available in a variable, it's possible to use a type cast of a pointer to that variable. The other option is to assign the value to a union and later read out the value using one of the other data elements sharing the union.

    The next alternative is to move all such floating point constants into a separate header file with named constants that you preprocess into their binary representation.

Reply
  • 0 in reply to Jürgen Breuer

    As I did write earlier, the floats will not take their binary representation until (not before) they are stored in memory.

    If the value is already available in a variable, it's possible to use a type cast of a pointer to that variable. The other option is to assign the value to a union and later read out the value using one of the other data elements sharing the union.

    The next alternative is to move all such floating point constants into a separate header file with named constants that you preprocess into their binary representation.

Children
  • 0 in reply to ImPer Westermark

    Now I got you!

    I tryed

    float f32ConstInitval = -12.5;
uint32_t ui32Testvalue = (*(uint32_t *)&f32ConstInitval);


    and got: 'scalar': initializer is not a constant :-(

    With

    static const float f32ConstInitval = -12.5;
uint32_t ui32Testvalue = f32ConstInitval);


    I got ui32Testvalue = 0xFFFFFFF4 as I asked my debugger :-(

    but with

    static const float f32ConstInitval = -12.5;
uint32_t ui32Testvalue = (*(uint32_t *)&f32ConstInitval);

    I yielded my desired ui32Testvalue = 0xC1480000 :-D
    with a litte overhead of 4 Bytes in far flash.

    Thanks a lot

    Jürgen

  • 0 in reply to Jürgen Breuer

    or to make a pointer (void or unsigned long) and points it to the floater.