1use core::convert::TryFrom;
2
3use crate::parser::Stream;
4
5#[derive(Clone, Copy, Debug)]
6pub(crate) struct DeltaSetIndexMap<'a> {
7 data: &'a [u8],
8}
9
10impl<'a> DeltaSetIndexMap<'a> {
11 #[inline]
12 pub(crate) fn new(data: &'a [u8]) -> Self {
13 DeltaSetIndexMap { data }
14 }
15
16 #[inline]
17 pub(crate) fn map(&self, mut index: u32) -> Option<(u16, u16)> {
18 let mut s = Stream::new(self.data);
19 let format = s.read::<u8>()?;
20 let entry_format = s.read::<u8>()?;
21 let map_count = if format == 0 {
22 s.read::<u16>()? as u32
23 } else {
24 s.read::<u32>()?
25 };
26
27 if map_count == 0 {
28 return None;
29 }
30
31 // 'If a given glyph ID is greater than mapCount-1, then the last entry is used.'
32 if index >= map_count {
33 index = map_count - 1;
34 }
35
36 let entry_size = ((entry_format >> 4) & 3) + 1;
37 let inner_index_bit_count = u32::from((entry_format & 0xF) + 1);
38
39 s.advance(usize::from(entry_size) * usize::try_from(index).ok()?);
40
41 let mut n = 0u32;
42 for b in s.read_bytes(usize::from(entry_size))? {
43 n = (n << 8) + u32::from(*b);
44 }
45
46 let outer_index = n >> inner_index_bit_count;
47 let inner_index = n & ((1 << inner_index_bit_count) - 1);
48 Some((
49 u16::try_from(outer_index).ok()?,
50 u16::try_from(inner_index).ok()?,
51 ))
52 }
53}
54