Unclear why serialized_size() yields different results

[henkery]

context: I am using bincode 1.3.3 in helping me parse a binary format that has mixed endianness when creating my own bincode from the default options I was suddenly struck with a error regarding trailing bytes. after some experimenting I find that creating a bincode from defaultoptions it expects a different amount of bytes to deserialize the same struct as when using the bincode::deserialize

I find that the following code:

let mut bincoder = bincode::DefaultOptions::new();
let mut reverse_bincoder = bincode::DefaultOptions::new();
bincoder.with_fixint_encoding();
reverse_bincoder.with_big_endian();
bincoder.with_little_endian();
reverse_bincoder.with_varint_encoding();

#[derive(Clone, Deserialize, Serialize)]
struct MacromediaFileHeader {
    file_size: u32,
    file_sign: [u8; 4], // CP1252 string
    imap: [u8; 4], // CP1252 string
    imap_length: u32,
    imap_unknown: u32,
    mmap_offset: u32,
}

let num = reverse_bincoder.serialized_size(&MacromediaFileHeader { file_sign: [0,0,0,0], file_size: 0, imap: [0,0,0,0], imap_length: 0, imap_unknown: 0, mmap_offset: 0}).unwrap();
let num3 = bincoder.serialized_size(&MacromediaFileHeader { file_sign: [0,0,0,0], file_size: 0, imap: [0,0,0,0], imap_length: 0, imap_unknown: 0, mmap_offset: 0}).unwrap();
let num3 = bincode::serialized_size(&MacromediaFileHeader { file_sign: [0,0,0,0], file_size: 0, imap: [0,0,0,0], imap_length: 0, imap_unknown: 0, mmap_offset: 0}).unwrap();

yields: num: 12 num2: 12 num3: 24

I experimented a bit and crawled though the docs but I cannot seem to understand what's going wrong here

[stale[bot]]

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