Rework all branching in the decoder
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parent
cbae67b07d
commit
899270e42e
1 changed files with 71 additions and 62 deletions
133
src/decode.rs
133
src/decode.rs
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@ -71,70 +71,79 @@ where
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// TODO: check for safety that ReadBuf is not over yet
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if run != 0 {
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run -= 1;
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} else {
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let b1 = buf.read();
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match b1 & QOI_MASK_2 {
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QOI_INDEX => {
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px = unsafe {
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// Safety: (b1 ^ QOI_INDEX) is guaranteed to be at most 6 bits
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*index.get_unchecked(usize::from(b1 ^ QOI_INDEX))
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};
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}
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QOI_DIFF_8 => {
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px.rgb_add(
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((b1 >> 4) & 0x03).wrapping_sub(2),
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((b1 >> 2) & 0x03).wrapping_sub(2),
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(b1 & 0x03).wrapping_sub(2),
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);
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}
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_ => match b1 & QOI_MASK_3 {
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QOI_RUN_8 => {
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run = u16::from(b1 & 0x1f);
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}
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QOI_RUN_16 => {
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run = 32 + ((u16::from(b1 & 0x1f) << 8) | u16::from(buf.read()));
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}
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QOI_DIFF_16 => {
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let b2 = buf.read();
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px.rgb_add(
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(b1 & 0x1f).wrapping_sub(16),
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(b2 >> 4).wrapping_sub(8),
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(b2 & 0x0f).wrapping_sub(8),
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);
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}
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_ => match b1 & QOI_MASK_4 {
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QOI_DIFF_24 => {
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let (b2, b3) = (buf.read(), buf.read());
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px.rgba_add(
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(((b1 & 0x0f) << 1) | (b2 >> 7)).wrapping_sub(16),
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((b2 & 0x7c) >> 2).wrapping_sub(16),
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(((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)).wrapping_sub(16),
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(b3 & 0x1f).wrapping_sub(16),
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);
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}
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QOI_COLOR => {
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if b1 & 8 != 0 {
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px.set_r(buf.read());
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}
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if b1 & 4 != 0 {
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px.set_g(buf.read());
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}
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if b1 & 2 != 0 {
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px.set_b(buf.read());
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}
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if b1 & 1 != 0 {
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px.set_a(buf.read());
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}
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}
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_ => {}
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},
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},
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}
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*px_out = px;
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continue;
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}
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unsafe {
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// Safety: hash_index() is computed mod 64, so it will never go out of bounds
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*index.get_unchecked_mut(usize::from(px.hash_index())) = px;
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let b1 = buf.read();
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match b1 >> 4 {
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0..=3 => {
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// QOI_INDEX
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px = unsafe {
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// Safety: (b1 ^ QOI_INDEX) is guaranteed to be at most 6 bits
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*index.get_unchecked(usize::from(b1 ^ QOI_INDEX))
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};
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}
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15 => {
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// QOI_COLOR
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if b1 & 8 != 0 {
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px.set_r(buf.read());
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}
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if b1 & 4 != 0 {
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px.set_g(buf.read());
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}
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if b1 & 2 != 0 {
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px.set_b(buf.read());
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}
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if b1 & 1 != 0 {
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px.set_a(buf.read());
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}
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}
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12..=13 => {
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// QOI_DIFF_16
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let b2 = buf.read();
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px.rgb_add(
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(b1 & 0x1f).wrapping_sub(16),
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(b2 >> 4).wrapping_sub(8),
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(b2 & 0x0f).wrapping_sub(8),
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);
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}
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14 => {
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// QOI_DIFF_24
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let (b2, b3) = (buf.read(), buf.read());
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px.rgba_add(
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(((b1 & 0x0f) << 1) | (b2 >> 7)).wrapping_sub(16),
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((b2 & 0x7c) >> 2).wrapping_sub(16),
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(((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)).wrapping_sub(16),
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(b3 & 0x1f).wrapping_sub(16),
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);
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}
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4..=5 => {
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// QOI_RUN_8
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run = u16::from(b1 & 0x1f);
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*px_out = px;
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continue;
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}
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8..=11 => {
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// QOI_DIFF_8
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px.rgb_add(
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((b1 >> 4) & 0x03).wrapping_sub(2),
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((b1 >> 2) & 0x03).wrapping_sub(2),
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(b1 & 0x03).wrapping_sub(2),
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);
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}
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6..=7 => {
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// QOI_RUN_16
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run = 32 + ((u16::from(b1 & 0x1f) << 8) | u16::from(buf.read()));
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*px_out = px;
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continue;
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}
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_ => {}
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}
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unsafe {
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// Safety: hash_index() is computed mod 64, so it will never go out of bounds
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*index.get_unchecked_mut(usize::from(px.hash_index())) = px;
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}
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*px_out = px;
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