Bit alingment

[Rundumeli]

Hi everyone

I have a problem with a data structure I really want to use, because I would heavenly benefit from the easy access, that it would provide.

/*
 * myTypes.h
 *
 *  Created on: 02.05.2023
 *      Author: 
 */

#ifndef INC_MYTYPES_H_
#define INC_MYTYPES_H_

#ifdef	__cplusplus
extern "C" {
#endif

#pragma pack(push, 1)

typedef union {
    struct {
        bool b0 : 1;
        bool b1 : 1;
        bool b2 : 1;
        bool b3 : 1;
        bool b4 : 1;
        bool b5 : 1;
        bool b6 : 1;
        bool b7 : 1;
        bool b8 : 1;
        bool b9 : 1;
        bool b10 : 1;
        bool b11 : 1;
        bool b12 : 1;
        bool b13 : 1;
        bool b14 : 1;
        bool b15 : 1;
        bool b16 : 1;
        bool b17 : 1;
        bool b18 : 1;
        bool b19 : 1;
        bool b20 : 1;
        bool b21 : 1;
        bool b22 : 1;
        bool b23 : 1;
        bool b24 : 1;
        bool b25 : 1;
        bool b26 : 1;
        bool b27 : 1;
        bool b28 : 1;
        bool b29 : 1;
        bool b30 : 1;
        bool b31 : 1;
    }BIT;
    bool BOOL[32];
    uint8_t INT8[4];
    uint16_t INT16[2];
    uint32_t INT32;
} bitarray32;

#pragma pack(pop)

#ifdef	__cplusplus
}
#endif

#endif /* INC_MYTYPES_H_ */

View more

The access via INT32, INT16 , INT8 and BIT is working, however over the BOOL array not really.

I understand, that I could have memory alignment issues, especially because I'm using this in c++. But that's why I have defined this types in c.
I tried to enforce alignment with #pragma pack(push, 1), but I'm way out of my knowledge here.

Can someone guide me through this. Thanks in advance.

[Tesla DeLorean]

C does not have a bit array type.

Typically if you want mechanical indexing you'd use the uint32_t type, and shift a bit mask. For a larger array you'd decompose a row/column based on the size of the type you're holding it in.

https://www.sanfoundry.com/c-program-implement-bit-array/

[Rundumeli]

Ohhh if it is only because I forgot to include stdbool.h, ... I would turn mad^^ Thanks for the reminder!

I know bit shifting, but as this example shows, indexing via the the bool/union/struct, the code gets much more readable. see:

//direct indexing via bool array
ptr_sequencer->ref_outputMaster.currentOutput.BOOL[chanelIndex] = channel.pattern.BOOL[32-
ptr_sequencer->ref_clkMaster.time];

//same result but with masks
ptr_sequencer->ref_outputMaster.currentOutput.INT8 = (channel.pattern.INT32 >> (32-ptr_sequencer->ref_clkMaster.time) & 1) << chanelIndex;

[Rundumeli]

Yeah no. that's not what caused the faulty behaviour....