384 lines
9.7 KiB
Rust
384 lines
9.7 KiB
Rust
//! Utility functions
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use std::iter::StepBy;
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use std::ops::Range;
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/// This iterator iterates over the different passes of an image Adam7 encoded
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/// PNG image
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/// The pattern is:
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/// 16462646
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/// 77777777
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/// 56565656
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/// 77777777
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/// 36463646
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/// 77777777
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/// 56565656
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/// 77777777
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///
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#[derive(Clone)]
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pub(crate) struct Adam7Iterator {
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line: u32,
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lines: u32,
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line_width: u32,
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current_pass: u8,
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width: u32,
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height: u32,
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}
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impl Adam7Iterator {
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pub fn new(width: u32, height: u32) -> Adam7Iterator {
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let mut this = Adam7Iterator {
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line: 0,
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lines: 0,
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line_width: 0,
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current_pass: 1,
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width,
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height,
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};
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this.init_pass();
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this
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}
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/// Calculates the bounds of the current pass
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fn init_pass(&mut self) {
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let w = f64::from(self.width);
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let h = f64::from(self.height);
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let (line_width, lines) = match self.current_pass {
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1 => (w / 8.0, h / 8.0),
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2 => ((w - 4.0) / 8.0, h / 8.0),
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3 => (w / 4.0, (h - 4.0) / 8.0),
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4 => ((w - 2.0) / 4.0, h / 4.0),
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5 => (w / 2.0, (h - 2.0) / 4.0),
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6 => ((w - 1.0) / 2.0, h / 2.0),
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7 => (w, (h - 1.0) / 2.0),
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_ => unreachable!(),
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};
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self.line_width = line_width.ceil() as u32;
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self.lines = lines.ceil() as u32;
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self.line = 0;
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}
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/// The current pass#.
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pub fn current_pass(&self) -> u8 {
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self.current_pass
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}
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}
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/// Iterates over the (passes, lines, widths)
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impl Iterator for Adam7Iterator {
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type Item = (u8, u32, u32);
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fn next(&mut self) -> Option<Self::Item> {
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if self.line < self.lines && self.line_width > 0 {
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let this_line = self.line;
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self.line += 1;
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Some((self.current_pass, this_line, self.line_width))
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} else if self.current_pass < 7 {
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self.current_pass += 1;
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self.init_pass();
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self.next()
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} else {
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None
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}
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}
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}
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fn subbyte_pixels(scanline: &[u8], bits_pp: usize) -> impl Iterator<Item = u8> + '_ {
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(0..scanline.len() * 8)
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.step_by(bits_pp)
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.map(move |bit_idx| {
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let byte_idx = bit_idx / 8;
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// sub-byte samples start in the high-order bits
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let rem = 8 - bit_idx % 8 - bits_pp;
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match bits_pp {
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// evenly divides bytes
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1 => (scanline[byte_idx] >> rem) & 1,
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2 => (scanline[byte_idx] >> rem) & 3,
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4 => (scanline[byte_idx] >> rem) & 15,
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_ => unreachable!(),
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}
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})
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}
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/// Given pass, image width, and line number, produce an iterator of bit positions of pixels to copy
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/// from the input scanline to the image buffer.
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fn expand_adam7_bits(
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pass: u8,
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width: usize,
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line_no: usize,
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bits_pp: usize,
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) -> StepBy<Range<usize>> {
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let (line_mul, line_off, samp_mul, samp_off) = match pass {
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1 => (8, 0, 8, 0),
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2 => (8, 0, 8, 4),
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3 => (8, 4, 4, 0),
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4 => (4, 0, 4, 2),
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5 => (4, 2, 2, 0),
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6 => (2, 0, 2, 1),
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7 => (2, 1, 1, 0),
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_ => panic!("Adam7 pass out of range: {}", pass),
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};
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// the equivalent line number in progressive scan
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let prog_line = line_mul * line_no + line_off;
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// line width is rounded up to the next byte
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let line_width = (width * bits_pp + 7) & !7;
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let line_start = prog_line * line_width;
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let start = line_start + (samp_off * bits_pp);
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let stop = line_start + (width * bits_pp);
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(start..stop).step_by(bits_pp * samp_mul)
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}
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/// Expands an Adam 7 pass
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pub fn expand_pass(
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img: &mut [u8],
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width: u32,
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scanline: &[u8],
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pass: u8,
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line_no: u32,
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bits_pp: u8,
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) {
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let width = width as usize;
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let line_no = line_no as usize;
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let bits_pp = bits_pp as usize;
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// pass is out of range but don't blow up
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if pass == 0 || pass > 7 {
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return;
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}
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let bit_indices = expand_adam7_bits(pass, width, line_no, bits_pp);
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if bits_pp < 8 {
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for (pos, px) in bit_indices.zip(subbyte_pixels(scanline, bits_pp)) {
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let rem = 8 - pos % 8 - bits_pp;
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img[pos / 8] |= px << rem as u8;
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}
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} else {
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let bytes_pp = bits_pp / 8;
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for (bitpos, px) in bit_indices.zip(scanline.chunks(bytes_pp)) {
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for (offset, val) in px.iter().enumerate() {
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img[bitpos / 8 + offset] = *val;
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}
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}
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}
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}
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#[test]
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fn test_adam7() {
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/*
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1646
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7777
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5656
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7777
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*/
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let it = Adam7Iterator::new(4, 4);
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let passes: Vec<_> = it.collect();
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assert_eq!(
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&*passes,
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&[
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(1, 0, 1),
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(4, 0, 1),
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(5, 0, 2),
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(6, 0, 2),
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(6, 1, 2),
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(7, 0, 4),
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(7, 1, 4)
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]
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);
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}
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#[test]
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fn test_subbyte_pixels() {
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let scanline = &[0b10101010, 0b10101010];
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let pixels = subbyte_pixels(scanline, 1).collect::<Vec<_>>();
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assert_eq!(pixels.len(), 16);
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assert_eq!(pixels, [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0]);
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}
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#[test]
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fn test_expand_adam7_bits() {
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let width = 32;
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let bits_pp = 1;
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let expected = |offset: usize, step: usize, count: usize| {
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(0..count)
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.map(move |i| step * i + offset)
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.collect::<Vec<_>>()
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};
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for line_no in 0..8 {
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let start = 8 * line_no * width;
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assert_eq!(
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expand_adam7_bits(1, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 8, 4)
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);
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let start = start + 4;
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assert_eq!(
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expand_adam7_bits(2, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 8, 4)
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);
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let start = (8 * line_no + 4) * width;
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assert_eq!(
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expand_adam7_bits(3, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 4, 8)
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);
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}
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for line_no in 0..16 {
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let start = 4 * line_no * width + 2;
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assert_eq!(
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expand_adam7_bits(4, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 4, 8)
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);
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let start = (4 * line_no + 2) * width;
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assert_eq!(
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expand_adam7_bits(5, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 2, 16)
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)
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}
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for line_no in 0..32 {
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let start = 2 * line_no * width + 1;
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assert_eq!(
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expand_adam7_bits(6, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 2, 16),
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"line_no: {}",
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line_no
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);
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let start = (2 * line_no + 1) * width;
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assert_eq!(
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expand_adam7_bits(7, width, line_no, bits_pp).collect::<Vec<_>>(),
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expected(start, 1, 32)
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);
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}
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}
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#[test]
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fn test_expand_pass_subbyte() {
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let mut img = [0u8; 8];
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let width = 8;
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let bits_pp = 1;
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expand_pass(&mut img, width, &[0b10000000], 1, 0, bits_pp);
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assert_eq!(img, [0b10000000u8, 0, 0, 0, 0, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b10000000], 2, 0, bits_pp);
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assert_eq!(img, [0b10001000u8, 0, 0, 0, 0, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b11000000], 3, 0, bits_pp);
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assert_eq!(img, [0b10001000u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b11000000], 4, 0, bits_pp);
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assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b11000000], 4, 1, bits_pp);
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assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10101010, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b11110000], 5, 0, bits_pp);
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assert_eq!(img, [0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0, 0]);
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expand_pass(&mut img, width, &[0b11110000], 5, 1, bits_pp);
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assert_eq!(
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img,
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[0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
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);
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expand_pass(&mut img, width, &[0b11110000], 6, 0, bits_pp);
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assert_eq!(
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img,
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[0b11111111u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
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);
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expand_pass(&mut img, width, &[0b11110000], 6, 1, bits_pp);
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assert_eq!(
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img,
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[0b11111111u8, 0, 0b11111111, 0, 0b10101010, 0, 0b10101010, 0]
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);
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expand_pass(&mut img, width, &[0b11110000], 6, 2, bits_pp);
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assert_eq!(
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img,
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[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b10101010, 0]
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);
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expand_pass(&mut img, width, &[0b11110000], 6, 3, bits_pp);
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assert_eq!(
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[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b11111111, 0],
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img
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);
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expand_pass(&mut img, width, &[0b11111111], 7, 0, bits_pp);
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assert_eq!(
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[
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0b11111111u8,
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0b11111111,
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0b11111111,
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0,
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0b11111111,
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0,
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0b11111111,
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0
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],
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img
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);
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expand_pass(&mut img, width, &[0b11111111], 7, 1, bits_pp);
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assert_eq!(
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[
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0b11111111u8,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0,
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0b11111111,
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0
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],
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img
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);
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expand_pass(&mut img, width, &[0b11111111], 7, 2, bits_pp);
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assert_eq!(
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[
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0b11111111u8,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0
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],
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img
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);
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expand_pass(&mut img, width, &[0b11111111], 7, 3, bits_pp);
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assert_eq!(
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[
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0b11111111u8,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111,
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0b11111111
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],
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img
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);
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}
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