Red is the least significant bit, because offsets start at bit #0. Endianness is not a concern because you have to specify the underlying integer type, and bit endianness is not a thing, so it's just the native endianness (if you, e.g., need a network format with specific endianness and a 32-bit bitfield, you can instead use 4 consecutive 8-bit bitfields laid out in a consistent way). Unspecified bits are ignored; they'll be zero if the bitfield is initialized through conventional means but if they can be accessed directly through the raw value (or e.g. through memcpy, pointer casting, and any other direct memory access means), but when reading a field only its specified bits are read so unspecified bits doesn't change that result. When writing to a field, the source value is truncated to the field size, so you never end up writing to other bits.
> Red is the least significant bit, because offsets start at bit #0.
So red is the LSB because you decided it was the LSB. That is not a by-definition thing.
> Endianness is not a concern because you have to specify the underlying integer type, and bit endianness is not a thing
That’s not actually true. There are formats which process bytes LSB to MSB, and formats which process them MSB to LSB. E.g. git’s offset-encoding, the leading byte is a bitmap of continuation bytes, bit 0 indicates whether byte 7 is present.
Both are perfectly justifiable, one is offset-based, while the other is visualisation-based as bytes are usually represented MSB-first (as binary numbers, essentially).
> but when reading a field only its specified bits are read so unspecified bits doesn't change that result. When writing to a field, the source value is truncated to the field size, so you never end up writing to other bits.
I’m quite confused by “bitfield” do you mean the container field (the one that’s actually defined by the `bitfield` keyword) or the contained sub-fields?
> I’m quite confused by “bitfield” do you mean the container field (the one that’s actually defined by the `bitfield` keyword) or the contained sub-fields?
