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//! Positioning (ROADMAP Phase 2): forward `pad_*`/`align_*` directives skip bits or
//! align to a byte boundary around a field, with typed amounts from `bnb::prelude`
//! (`4.bits()`, `1.bytes()`). Backward `seek`/`restore_position` need `SeekSource`
//! (Phase 3).
use bnb::prelude::*;
use bnb::{bin, u4};
#[bin]
#[derive(Debug, PartialEq, Eq, Clone)]
struct Frame {
tag: u4,
#[br(pad_before = 4.bits())] // 4 reserved bits between tag and value
value: u8,
#[br(align_after)] // pad to a byte boundary after the (here already-aligned) field
trailer: u4,
}
#[test]
fn pad_and_align_round_trip() {
let f = Frame {
tag: u4::new(0x5),
value: 0xAB,
trailer: u4::new(0x3),
};
let bytes = f.to_bytes().unwrap();
// tag(0101) pad(0000) | value(0xAB) | trailer(0011) pad-to-byte(0000)
assert_eq!(bytes, [0x50, 0xAB, 0x30]);
assert_eq!(Frame::decode_exact(&bytes).unwrap(), f);
}
// A whole-byte pad expressed in bytes.
#[bin]
#[derive(Debug, PartialEq, Eq, Clone)]
struct Spaced {
a: u4,
#[br(pad_before = 1.bytes())] // skip a full byte
b: u4,
}
#[test]
fn byte_sized_pad() {
let f = Spaced {
a: u4::new(0xA),
b: u4::new(0xB),
};
let bytes = f.to_bytes().unwrap();
// a(1010) pad-hi(0000) | pad-lo(0000 0000)? -> a at 0..4, pad 4..12, b 12..16
// byte0 = 1010_0000, byte1 = 0000_1011
assert_eq!(bytes, [0xA0, 0x0B]);
assert_eq!(Spaced::decode_exact(&bytes).unwrap(), f);
}