How Can I Efficiently Convert Between Eight Boolean Values and a Single Byte?

Merging and Decoding Bytes into Boolean Values

In some programming scenarios, it becomes necessary to manipulate binary data at a bit level. One such task involves converting eight boolean values into a single byte and vice versa. This article explores efficient methods to accomplish this conversion.

Converting Boolean Values to Byte

The simplest approach to merging boolean values into a byte is through bitwise operations. Each boolean value corresponds to a bit position in the byte, with 'true' assigned to '1' and 'false' to '0'. By iteratively shifting '1' left based on the boolean value and ORing it with the accumulating result, a byte can be constructed. This process is exemplified in the following function:

unsigned char ToByte(bool b[8])
{
    unsigned char c = 0;
    for (int i=0; i < 8; ++i)
        if (b[i])
            c |= 1 << i;
    return c;
}

Decoding a Byte into Boolean Values

Conversely, decoding a byte into individual boolean values requires a similar iterative process. By shifting the byte right and comparing it against a '1' mask, each bit position can be extracted and assigned a boolean value of 'true' for '1' and 'false' for '0'. The following function implements this process:

void FromByte(unsigned char c, bool b[8])
{
    for (int i=0; i < 8; ++i)
        b[i] = (c & (1<<i)) != 0;
}

Bitfield Approach

An alternative and potentially more elegant approach utilizes bitfields and unions. By defining a structure with eight 1-bit fields, each boolean value can be assigned directly to the corresponding field. Unioning this structure with an unsigned char allows effortless conversion between the two data types. This is achieved through the following code snippet:

struct Bits
{
    unsigned b0:1, b1:1, b2:1, b3:1, b4:1, b5:1, b6:1, b7:1;
};

union CBits
{
    Bits bits;
    unsigned char byte;
};

By assigning values to either member of the union, the conversion is automatically performed. However, it is crucial to note that bitfield order and potential padding may vary depending on the implementation.

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