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Rework all branching in the decoder

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This commit is contained in:
Ivan Smirnov 2021-11-29 11:30:09 +00:00
parent cbae67b07d
commit 899270e42e
1 changed files with 71 additions and 62 deletions
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87
src/decode.rs
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@ -71,48 +71,21 @@ where
// TODO: check for safety that ReadBuf is not over yet
if run != 0 {
run -= 1;
} else {
*px_out = px;
continue;
}
let b1 = buf.read();
match b1 & QOI_MASK_2 {
QOI_INDEX => {
match b1 >> 4 {
0..=3 => {
// QOI_INDEX
px = unsafe {
// Safety: (b1 ^ QOI_INDEX) is guaranteed to be at most 6 bits
*index.get_unchecked(usize::from(b1 ^ QOI_INDEX))
};
}
QOI_DIFF_8 => {
px.rgb_add(
((b1 >> 4) & 0x03).wrapping_sub(2),
((b1 >> 2) & 0x03).wrapping_sub(2),
(b1 & 0x03).wrapping_sub(2),
);
}
_ => match b1 & QOI_MASK_3 {
QOI_RUN_8 => {
run = u16::from(b1 & 0x1f);
}
QOI_RUN_16 => {
run = 32 + ((u16::from(b1 & 0x1f) << 8) | u16::from(buf.read()));
}
QOI_DIFF_16 => {
let b2 = buf.read();
px.rgb_add(
(b1 & 0x1f).wrapping_sub(16),
(b2 >> 4).wrapping_sub(8),
(b2 & 0x0f).wrapping_sub(8),
);
}
_ => match b1 & QOI_MASK_4 {
QOI_DIFF_24 => {
let (b2, b3) = (buf.read(), buf.read());
px.rgba_add(
(((b1 & 0x0f) << 1) | (b2 >> 7)).wrapping_sub(16),
((b2 & 0x7c) >> 2).wrapping_sub(16),
(((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)).wrapping_sub(16),
(b3 & 0x1f).wrapping_sub(16),
);
}
QOI_COLOR => {
15 => {
// QOI_COLOR
if b1 & 8 != 0 {
px.set_r(buf.read());
}
@ -126,16 +99,52 @@ where
px.set_a(buf.read());
}
}
12..=13 => {
// QOI_DIFF_16
let b2 = buf.read();
px.rgb_add(
(b1 & 0x1f).wrapping_sub(16),
(b2 >> 4).wrapping_sub(8),
(b2 & 0x0f).wrapping_sub(8),
);
}
14 => {
// QOI_DIFF_24
let (b2, b3) = (buf.read(), buf.read());
px.rgba_add(
(((b1 & 0x0f) << 1) | (b2 >> 7)).wrapping_sub(16),
((b2 & 0x7c) >> 2).wrapping_sub(16),
(((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)).wrapping_sub(16),
(b3 & 0x1f).wrapping_sub(16),
);
}
4..=5 => {
// QOI_RUN_8
run = u16::from(b1 & 0x1f);
*px_out = px;
continue;
}
8..=11 => {
// QOI_DIFF_8
px.rgb_add(
((b1 >> 4) & 0x03).wrapping_sub(2),
((b1 >> 2) & 0x03).wrapping_sub(2),
(b1 & 0x03).wrapping_sub(2),
);
}
6..=7 => {
// QOI_RUN_16
run = 32 + ((u16::from(b1 & 0x1f) << 8) | u16::from(buf.read()));
*px_out = px;
continue;
}
_ => {}
},
},
}
unsafe {
// Safety: hash_index() is computed mod 64, so it will never go out of bounds
*index.get_unchecked_mut(usize::from(px.hash_index())) = px;
}
}
*px_out = px;
}