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pub(crate) const VAR_INT_BUF_SIZE: usize = 5;
pub(crate) fn get_sized_buf(buf: &mut Option<Vec<u8>>, offset: usize, size: usize) -> &mut [u8] {
let end_at = offset + size;
loop {
match buf {
Some(v) => {
ensure_buf_has_size(v, end_at);
break &mut v[offset..end_at];
}
None => {
let new_buf = Vec::with_capacity(end_at);
*buf = Some(new_buf);
}
}
}
}
fn ensure_buf_has_size(buf: &mut Vec<u8>, total_size: usize) {
let cur_len = buf.len();
if cur_len >= total_size {
return;
}
let additional = total_size - cur_len;
buf.reserve(additional);
unsafe {
let start_at = buf.as_mut_ptr();
let start_write_at = start_at.offset(cur_len as isize);
std::ptr::write_bytes(start_write_at, 0, additional);
buf.set_len(total_size);
}
}
pub(crate) fn move_data_rightwards(target: &mut [u8], size: usize, shift_amount: usize) {
let required_len = size + shift_amount;
let actual_len = target.len();
if actual_len < required_len {
panic!(
"move of data to the right (0..{} -> {}..{}) exceeds size of buffer {}",
size, shift_amount, required_len, actual_len,
)
}
unsafe { move_data_rightwards_unchecked(target, size, shift_amount) }
}
unsafe fn move_data_rightwards_unchecked(target: &mut [u8], size: usize, shift_amount: usize) {
if shift_amount == 0 {
return;
}
let src_ptr = target.as_mut_ptr();
let dst_ptr = src_ptr.offset(shift_amount as isize);
std::ptr::copy(src_ptr, dst_ptr, size);
}
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