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//! Arithmetic scan decoding for JPEG.
//!
//! This module handles decoding of arithmetic-coded JPEG scans (SOF9/SOF10).
use crate::entropy::ArithmeticDecoder;
use crate::error::{Error, Result, ScanRead};
use crate::foundation::alloc::{checked_size_2d, try_alloc_dct_blocks, try_alloc_filled};
use enough::Stop;
use super::JpegParser;
/// Arithmetic scan decoding methods for JpegParser.
impl<'a> JpegParser<'a> {
/// Decode an arithmetic-coded sequential scan.
///
/// The `stop` parameter allows cancellation of long-running decodes.
pub(super) fn decode_arithmetic_scan(
&mut self,
scan_components: &[(usize, u8, u8)],
stop: &impl Stop,
) -> Result<()> {
// DNL mode not supported
if self.height == 0 {
return Err(Error::unsupported_feature(
"DNL mode (height=0 in SOF) not yet supported for arithmetic scan decoding",
));
}
// Calculate MCU structure
let mut max_h_samp = 1u8;
let mut max_v_samp = 1u8;
for i in 0..self.num_components as usize {
max_h_samp = max_h_samp.max(self.components[i].h_samp_factor);
max_v_samp = max_v_samp.max(self.components[i].v_samp_factor);
}
let mcu_width = (max_h_samp as usize) * 8;
let mcu_height = (max_v_samp as usize) * 8;
let mcu_cols = (self.width as usize + mcu_width - 1) / mcu_width;
let mcu_rows = (self.height as usize + mcu_height - 1) / mcu_height;
// Initialize coefficient storage
if self.coeffs.is_empty() {
for i in 0..self.num_components as usize {
let h_samp = self.components[i].h_samp_factor as usize;
let v_samp = self.components[i].v_samp_factor as usize;
let comp_blocks_h = checked_size_2d(mcu_cols, h_samp)?;
let comp_blocks_v = checked_size_2d(mcu_rows, v_samp)?;
let num_blocks = checked_size_2d(comp_blocks_h, comp_blocks_v)?;
self.coeffs.push(try_alloc_dct_blocks(
num_blocks,
"allocating DCT coefficients",
)?);
self.coeff_counts.push(try_alloc_filled(
num_blocks,
64u8,
"allocating coefficient counts",
)?);
self.nonzero_bitmaps.push(try_alloc_filled(
num_blocks,
0u64,
"allocating nonzero bitmaps",
)?);
}
}
// Set up arithmetic decoder
let scan_data = &self.data[self.position..];
let mut decoder = ArithmeticDecoder::new(scan_data);
// Configure decoder with conditioning parameters and restart interval
decoder.set_restart_interval(self.restart_interval);
for tbl in 0..4 {
let (l, u) = self.arith_dc_cond[tbl];
decoder.set_dc_conditioning(tbl, l, u);
decoder.set_ac_conditioning(tbl, self.arith_ac_kx[tbl]);
}
// Reset decoder for this scan
decoder.reset_for_scan();
// Decode MCUs
for mcu_y in 0..mcu_rows {
// Check for cancellation at each MCU row
if stop.should_stop() {
return Err(Error::cancelled());
}
for mcu_x in 0..mcu_cols {
// For each component in the scan
for (comp_idx, dc_table, ac_table) in scan_components {
let h_samp = self.components[*comp_idx].h_samp_factor as usize;
let v_samp = self.components[*comp_idx].v_samp_factor as usize;
let comp_blocks_h = mcu_cols * h_samp;
// Decode all blocks for this component in this MCU
for v in 0..v_samp {
for h in 0..h_samp {
let block_x = mcu_x * h_samp + h;
let block_y = mcu_y * v_samp + v;
let block_idx = block_y * comp_blocks_h + block_x;
// Decode block
match decoder.decode_block(
&mut self.coeffs[*comp_idx][block_idx],
*comp_idx,
*dc_table as usize,
*ac_table as usize,
)? {
ScanRead::Value(()) => {
// Count non-zero coefficients (approximation for tiered IDCT)
let block = &self.coeffs[*comp_idx][block_idx];
let mut count = 0u8;
for (i, &coef) in block.iter().enumerate() {
if coef != 0 {
count = (i + 1) as u8;
}
}
self.coeff_counts[*comp_idx][block_idx] = count.max(1);
}
ScanRead::EndOfScan | ScanRead::Truncated => {
// Handle truncation - zero remaining blocks
self.coeffs[*comp_idx][block_idx] = [0i16; 64];
self.coeff_counts[*comp_idx][block_idx] = 1;
}
}
}
}
}
}
}
self.position += decoder.position();
Ok(())
}
/// Decode an arithmetic-coded progressive scan.
///
/// The `stop` parameter allows cancellation of long-running decodes.
pub(super) fn decode_arithmetic_progressive_scan(
&mut self,
scan_components: &[(usize, u8, u8)],
ss: u8,
se: u8,
ah: u8,
al: u8,
stop: &impl Stop,
) -> Result<()> {
// DNL mode not supported
if self.height == 0 {
return Err(Error::unsupported_feature(
"DNL mode (height=0 in SOF) not supported for progressive scan",
));
}
// Calculate MCU structure
let mut max_h_samp = 1u8;
let mut max_v_samp = 1u8;
for i in 0..self.num_components as usize {
max_h_samp = max_h_samp.max(self.components[i].h_samp_factor);
max_v_samp = max_v_samp.max(self.components[i].v_samp_factor);
}
let mcu_width = (max_h_samp as usize) * 8;
let mcu_height = (max_v_samp as usize) * 8;
let mcu_cols = (self.width as usize + mcu_width - 1) / mcu_width;
let mcu_rows = (self.height as usize + mcu_height - 1) / mcu_height;
// Initialize coefficient storage if needed
if self.coeffs.is_empty() {
for i in 0..self.num_components as usize {
let h_samp = self.components[i].h_samp_factor as usize;
let v_samp = self.components[i].v_samp_factor as usize;
let comp_blocks_h = checked_size_2d(mcu_cols, h_samp)?;
let comp_blocks_v = checked_size_2d(mcu_rows, v_samp)?;
let num_blocks = checked_size_2d(comp_blocks_h, comp_blocks_v)?;
self.coeffs.push(try_alloc_dct_blocks(
num_blocks,
"allocating DCT coefficients",
)?);
self.coeff_counts.push(try_alloc_filled(
num_blocks,
64u8,
"allocating coefficient counts",
)?);
self.nonzero_bitmaps.push(try_alloc_filled(
num_blocks,
0u64,
"allocating nonzero bitmaps",
)?);
}
}
// Set up arithmetic decoder
let scan_data = &self.data[self.position..];
let mut decoder = ArithmeticDecoder::new(scan_data);
// Configure decoder
decoder.set_restart_interval(self.restart_interval);
for tbl in 0..4 {
let (l, u) = self.arith_dc_cond[tbl];
decoder.set_dc_conditioning(tbl, l, u);
decoder.set_ac_conditioning(tbl, self.arith_ac_kx[tbl]);
}
// Reset for scan (clears stats appropriate for this scan type)
decoder.reset_for_scan();
let is_dc_scan = ss == 0;
let is_first_scan = ah == 0;
if is_dc_scan {
// DC scan
if is_first_scan {
self.decode_arith_dc_first(
&mut decoder,
scan_components,
mcu_cols,
mcu_rows,
al,
stop,
)?;
} else {
self.decode_arith_dc_refine(
&mut decoder,
scan_components,
mcu_cols,
mcu_rows,
al,
stop,
)?;
}
} else {
// AC scan (single component only)
if scan_components.len() != 1 {
return Err(Error::invalid_jpeg_data(
"progressive AC scan must have exactly one component",
));
}
let (comp_idx, _dc_tbl, ac_tbl) = scan_components[0];
if is_first_scan {
self.decode_arith_ac_first(
&mut decoder,
comp_idx,
ac_tbl as usize,
mcu_cols,
mcu_rows,
ss,
se,
al,
stop,
)?;
} else {
self.decode_arith_ac_refine(
&mut decoder,
comp_idx,
ac_tbl as usize,
mcu_cols,
mcu_rows,
ss,
se,
al,
stop,
)?;
}
}
self.position += decoder.position();
Ok(())
}
/// Decode DC first scan (progressive arithmetic).
fn decode_arith_dc_first(
&mut self,
decoder: &mut ArithmeticDecoder,
scan_components: &[(usize, u8, u8)],
mcu_cols: usize,
mcu_rows: usize,
al: u8,
stop: &impl Stop,
) -> Result<()> {
for mcu_y in 0..mcu_rows {
// Check for cancellation at each MCU row
if stop.should_stop() {
return Err(Error::cancelled());
}
for mcu_x in 0..mcu_cols {
for (comp_idx, dc_tbl, _ac_tbl) in scan_components {
let h_samp = self.components[*comp_idx].h_samp_factor as usize;
let v_samp = self.components[*comp_idx].v_samp_factor as usize;
let comp_blocks_h = mcu_cols * h_samp;
for v in 0..v_samp {
for h in 0..h_samp {
let block_x = mcu_x * h_samp + h;
let block_y = mcu_y * v_samp + v;
let block_idx = block_y * comp_blocks_h + block_x;
match decoder.decode_dc_first(*comp_idx, *dc_tbl as usize, al)? {
ScanRead::Value(dc) => {
self.coeffs[*comp_idx][block_idx][0] = dc;
}
ScanRead::EndOfScan | ScanRead::Truncated => {
// Truncated - leave as zero
}
}
}
}
}
}
}
Ok(())
}
/// Decode DC refinement scan (progressive arithmetic).
fn decode_arith_dc_refine(
&mut self,
decoder: &mut ArithmeticDecoder,
scan_components: &[(usize, u8, u8)],
mcu_cols: usize,
mcu_rows: usize,
al: u8,
stop: &impl Stop,
) -> Result<()> {
for mcu_y in 0..mcu_rows {
// Check for cancellation at each MCU row
if stop.should_stop() {
return Err(Error::cancelled());
}
for mcu_x in 0..mcu_cols {
for (comp_idx, _dc_tbl, _ac_tbl) in scan_components {
let h_samp = self.components[*comp_idx].h_samp_factor as usize;
let v_samp = self.components[*comp_idx].v_samp_factor as usize;
let comp_blocks_h = mcu_cols * h_samp;
for v in 0..v_samp {
for h in 0..h_samp {
let block_x = mcu_x * h_samp + h;
let block_y = mcu_y * v_samp + v;
let block_idx = block_y * comp_blocks_h + block_x;
decoder.decode_dc_refine(&mut self.coeffs[*comp_idx][block_idx], al)?;
}
}
}
}
}
Ok(())
}
/// Decode AC first scan (progressive arithmetic).
#[allow(clippy::too_many_arguments)]
fn decode_arith_ac_first(
&mut self,
decoder: &mut ArithmeticDecoder,
comp_idx: usize,
ac_tbl: usize,
mcu_cols: usize,
mcu_rows: usize,
ss: u8,
se: u8,
al: u8,
stop: &impl Stop,
) -> Result<()> {
let h_samp = self.components[comp_idx].h_samp_factor as usize;
let v_samp = self.components[comp_idx].v_samp_factor as usize;
let comp_blocks_h = mcu_cols * h_samp;
let comp_blocks_v = mcu_rows * v_samp;
// AC progressive scans process blocks in raster order (not MCU order)
for block_y in 0..comp_blocks_v {
// Check for cancellation at each block row
if stop.should_stop() {
return Err(Error::cancelled());
}
for block_x in 0..comp_blocks_h {
let block_idx = block_y * comp_blocks_h + block_x;
decoder.decode_ac_first(
&mut self.coeffs[comp_idx][block_idx],
&mut self.nonzero_bitmaps[comp_idx][block_idx],
ac_tbl,
ss,
se,
al,
)?;
}
}
Ok(())
}
/// Decode AC refinement scan (progressive arithmetic).
#[allow(clippy::too_many_arguments)]
fn decode_arith_ac_refine(
&mut self,
decoder: &mut ArithmeticDecoder,
comp_idx: usize,
ac_tbl: usize,
mcu_cols: usize,
mcu_rows: usize,
ss: u8,
se: u8,
al: u8,
stop: &impl Stop,
) -> Result<()> {
let h_samp = self.components[comp_idx].h_samp_factor as usize;
let v_samp = self.components[comp_idx].v_samp_factor as usize;
let comp_blocks_h = mcu_cols * h_samp;
let comp_blocks_v = mcu_rows * v_samp;
for block_y in 0..comp_blocks_v {
// Check for cancellation at each block row
if stop.should_stop() {
return Err(Error::cancelled());
}
for block_x in 0..comp_blocks_h {
let block_idx = block_y * comp_blocks_h + block_x;
decoder.decode_ac_refine(
&mut self.coeffs[comp_idx][block_idx],
&mut self.nonzero_bitmaps[comp_idx][block_idx],
ac_tbl,
ss,
se,
al,
)?;
}
}
Ok(())
}
}