How Can We Efficiently Encode and Decode Eight Booleans into a Single Byte?

Creating and Decoding Bytes of Booleans

Efficiently merging boolean values into a compact representation is a common task in programming. This article explores two methods to achieve this, focusing on converting eight booleans into a single byte.

From Booleans to Byte

The "hard way" involves iterating through the boolean array, setting specific bits of the byte to 1 or 0 based on the boolean values. This approach ensures explicit control over the bit manipulation.

From Byte to Booleans

Similarly, the "hard way" involves another iteration, this time extracting individual bits from the byte and assigning them to the boolean array.

The Cool Way: Bitfields and Unions

An alternative approach leverages bitfields and unions. By declaring a struct with eight bitfields and a union that contains both the struct and an unsigned char, we can directly assign to one member and read from another. However, it's important to note that the order of bits in the struct is implementation-dependent.

Portability Considerations

While reading from one union member after writing to another is generally well-defined in C99 and some C compilers, it's considered undefined behavior in ISO C . To avoid this issue, using memcpy or C 20 std::bit_cast ensures safe type-punning in portable code.

Additional Considerations

The bit order within a character and any potential padding between bitfield members are also implementation-dependent, requiring careful consideration in cross-platform applications.

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