j2k_types/

lib.rs

// j2k-coverage: shared-accelerator-host
//! Shared JPEG 2000 and HTJ2K encode-stage contracts and helpers for j2k.
//!
//! This crate is the neutral public contract between the `j2k` facade, the
//! `j2k-native` codec engine, and device adapters. It defines encode-stage
//! jobs, outputs, dispatch reports, progression-order helpers, the shared
//! accelerator trait, and its default CPU-only implementation.

#![no_std]
#![forbid(unsafe_code)]
#![forbid(missing_docs)]

extern crate alloc;

use alloc::vec::Vec;
use core::ops::Range;

mod decode_payload;
pub use decode_payload::{
    HtCodeBlockPayloadRanges, J2kClassicCodeBlockPayload, J2kCodestreamRange,
};
mod limits;
#[doc(hidden)]
pub use limits::{MAX_JPEG2000_PART1_COMPONENTS, MAX_JPEG2000_PART1_SAMPLE_BIT_DEPTH};
mod resident;
#[doc(hidden)]
pub use resident::{
    J2kResidentEncodeInput, J2kResidentEncodeInputError, J2kResidentHtj2kTileEncodeJob,
};
mod stage_error;
pub use stage_error::{J2kEncodeStageError, J2kEncodeStageErrorKind, J2kEncodeStageResult};

/// Adapter classic J2K sub-band kind for backend experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum J2kSubBandType {
    /// Low-low sub-band.
    LowLow,
    /// High-low sub-band.
    HighLow,
    /// Low-high sub-band.
    LowHigh,
    /// High-high sub-band.
    HighHigh,
}

/// Adapter classic J2K code-block style for backend experimentation.
#[derive(Debug, Clone, Copy)]
#[expect(
    clippy::struct_excessive_bools,
    reason = "the five booleans model independent JPEG 2000 COD code-block style flags"
)]
pub struct J2kCodeBlockStyle {
    /// Selective arithmetic coding bypass was enabled.
    pub selective_arithmetic_coding_bypass: bool,
    /// Context probabilities reset after each pass.
    pub reset_context_probabilities: bool,
    /// Coding terminated after each pass.
    pub termination_on_each_pass: bool,
    /// Vertically causal context was enabled.
    pub vertically_causal_context: bool,
    /// Segmentation symbols were enabled.
    pub segmentation_symbols: bool,
}

/// Adapter classic J2K coded segment for backend experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct J2kCodeBlockSegment {
    /// Byte offset of this segment within the combined payload.
    pub data_offset: u32,
    /// Segment payload length in bytes.
    pub data_length: u32,
    /// First coding pass covered by this segment.
    pub start_coding_pass: u8,
    /// One-past-last coding pass covered by this segment.
    pub end_coding_pass: u8,
    /// Whether this segment is decoded through the arithmetic path.
    pub use_arithmetic: bool,
}

/// Adapter encoded classic J2K code-block payload for backend experimentation.
#[derive(Debug)]
pub struct EncodedJ2kCodeBlock {
    /// Combined payload bytes for all coded segments in this code block.
    pub data: Vec<u8>,
    /// Coded segments for the code block.
    pub segments: Vec<J2kCodeBlockSegment>,
    /// Number of coding passes present for this code block.
    pub number_of_coding_passes: u8,
    /// Missing most-significant bit planes for this code block.
    pub missing_bit_planes: u8,
}

/// Adapter encoded HTJ2K cleanup/refinement code-block payload for backend experimentation.
#[derive(Debug)]
pub struct EncodedHtJ2kCodeBlock {
    /// Combined cleanup/refinement bytes for this code block.
    pub data: Vec<u8>,
    /// Cleanup segment length in bytes.
    pub cleanup_length: u32,
    /// Refinement segment length in bytes.
    pub refinement_length: u32,
    /// Number of coding passes present for this code block.
    pub num_coding_passes: u8,
    /// Number of zero most-significant bitplanes before first inclusion.
    pub num_zero_bitplanes: u8,
}

/// Adapter pixel deinterleave/level-shift job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kDeinterleaveToF32Job<'a> {
    /// Interleaved source pixel bytes.
    pub pixels: &'a [u8],
    /// Number of pixels to convert.
    pub num_pixels: usize,
    /// Number of interleaved components per pixel.
    pub num_components: u16,
    /// Source sample bit depth.
    pub bit_depth: u8,
    /// Whether source samples are signed.
    pub signed: bool,
}

/// Adapter forward RCT job for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardRctJob<'a> {
    /// First component plane, updated in place.
    pub plane0: &'a mut [f32],
    /// Second component plane, updated in place.
    pub plane1: &'a mut [f32],
    /// Third component plane, updated in place.
    pub plane2: &'a mut [f32],
}

/// Adapter forward ICT job for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardIctJob<'a> {
    /// First component plane, updated in place.
    pub plane0: &'a mut [f32],
    /// Second component plane, updated in place.
    pub plane1: &'a mut [f32],
    /// Third component plane, updated in place.
    pub plane2: &'a mut [f32],
}

/// Adapter forward 5/3 DWT job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kForwardDwt53Job<'a> {
    /// Source samples in row-major order.
    pub samples: &'a [f32],
    /// Source width in samples.
    pub width: u32,
    /// Source height in samples.
    pub height: u32,
    /// Number of decomposition levels requested.
    pub num_levels: u8,
}

/// Adapter forward 5/3 DWT output for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardDwt53Output {
    /// LL subband coefficients from the lowest decomposition level.
    pub ll: Vec<f32>,
    /// LL subband width.
    pub ll_width: u32,
    /// LL subband height.
    pub ll_height: u32,
    /// Higher resolution detail levels, ordered from lowest to highest.
    pub levels: Vec<J2kForwardDwt53Level>,
}

/// Adapter forward 5/3 DWT detail level for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardDwt53Level {
    /// HL subband coefficients.
    pub hl: Vec<f32>,
    /// LH subband coefficients.
    pub lh: Vec<f32>,
    /// HH subband coefficients.
    pub hh: Vec<f32>,
    /// Full-resolution width represented by this level.
    pub width: u32,
    /// Full-resolution height represented by this level.
    pub height: u32,
    /// Low-pass width at this level.
    pub low_width: u32,
    /// Low-pass height at this level.
    pub low_height: u32,
    /// High-pass width at this level.
    pub high_width: u32,
    /// High-pass height at this level.
    pub high_height: u32,
}

/// Adapter forward irreversible 9/7 DWT job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kForwardDwt97Job<'a> {
    /// Source samples in row-major order.
    pub samples: &'a [f32],
    /// Source width in samples.
    pub width: u32,
    /// Source height in samples.
    pub height: u32,
    /// Number of decomposition levels requested.
    pub num_levels: u8,
}

/// Adapter forward 9/7 DWT output for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardDwt97Output {
    /// LL subband coefficients from the lowest decomposition level.
    pub ll: Vec<f32>,
    /// LL subband width.
    pub ll_width: u32,
    /// LL subband height.
    pub ll_height: u32,
    /// Higher resolution detail levels, ordered from lowest to highest.
    pub levels: Vec<J2kForwardDwt97Level>,
}

/// Adapter forward 9/7 DWT detail level for backend experimentation.
#[derive(Debug)]
pub struct J2kForwardDwt97Level {
    /// HL subband coefficients.
    pub hl: Vec<f32>,
    /// LH subband coefficients.
    pub lh: Vec<f32>,
    /// HH subband coefficients.
    pub hh: Vec<f32>,
    /// Full-resolution width represented by this level.
    pub width: u32,
    /// Full-resolution height represented by this level.
    pub height: u32,
    /// Low-pass width at this level.
    pub low_width: u32,
    /// Low-pass height at this level.
    pub low_height: u32,
    /// High-pass width at this level.
    pub high_width: u32,
    /// High-pass height at this level.
    pub high_height: u32,
}

/// Adapter sub-band quantization job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kQuantizeSubbandJob<'a> {
    /// Source sub-band coefficients in row-major order.
    pub coefficients: &'a [f32],
    /// Quantization step-size exponent.
    pub step_exponent: u16,
    /// Quantization step-size mantissa.
    pub step_mantissa: u16,
    /// Nominal range bits for this sub-band.
    pub range_bits: u8,
    /// Whether to use reversible integer quantization.
    pub reversible: bool,
}

/// Adapter Tier-1 classic J2K code-block encode job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kTier1CodeBlockEncodeJob<'a> {
    /// Quantized coefficients in row-major order.
    pub coefficients: &'a [i32],
    /// Code-block width in samples.
    pub width: u32,
    /// Code-block height in samples.
    pub height: u32,
    /// Subband kind containing this code-block.
    pub sub_band_type: J2kSubBandType,
    /// Total bitplanes for this subband/code-block.
    pub total_bitplanes: u8,
    /// Classic J2K code-block style flags.
    pub style: J2kCodeBlockStyle,
}

/// Adapter HTJ2K code-block encode job for backend experimentation.
#[derive(Debug, Clone, Copy)]
pub struct J2kHtCodeBlockEncodeJob<'a> {
    /// Quantized coefficients in row-major order.
    pub coefficients: &'a [i32],
    /// Code-block width in samples.
    pub width: u32,
    /// Code-block height in samples.
    pub height: u32,
    /// Total bitplanes for this subband/code-block.
    pub total_bitplanes: u8,
    /// Requested HT coding passes for this contribution.
    ///
    /// `1` is cleanup-only. `2` requests cleanup plus significance-propagation
    /// refinement on the native CPU path. `3` additionally requests one
    /// magnitude-refinement pass. Higher values require an accelerator and
    /// must not be silently reduced by CPU fallback.
    pub target_coding_passes: u8,
}

/// Adapter HTJ2K cleanup/refinement encode job for one unquantized sub-band.
#[derive(Debug, Clone, Copy)]
pub struct J2kHtSubbandEncodeJob<'a> {
    /// Source sub-band coefficients in row-major order.
    pub coefficients: &'a [f32],
    /// Sub-band width in samples.
    pub width: u32,
    /// Sub-band height in samples.
    pub height: u32,
    /// Quantization step-size exponent.
    pub step_exponent: u16,
    /// Quantization step-size mantissa.
    pub step_mantissa: u16,
    /// Nominal range bits for this sub-band.
    pub range_bits: u8,
    /// Whether to use reversible integer quantization.
    pub reversible: bool,
    /// Code-block width in samples.
    pub code_block_width: u32,
    /// Code-block height in samples.
    pub code_block_height: u32,
    /// Total coded bitplanes for this sub-band.
    pub total_bitplanes: u8,
}

/// Adapter HTJ2K tile-body encode job for backend-resident full-tile paths.
#[derive(Debug, Clone, Copy)]
pub struct J2kHtj2kTileEncodeJob<'a> {
    /// Interleaved source pixel bytes.
    pub pixels: &'a [u8],
    /// Tile/image width in samples.
    pub width: u32,
    /// Tile/image height in samples.
    pub height: u32,
    /// Number of interleaved image components.
    pub num_components: u16,
    /// Source component bit depth.
    pub bit_depth: u8,
    /// Whether source samples are signed.
    pub signed: bool,
    /// Number of DWT decomposition levels.
    pub num_decomposition_levels: u8,
    /// Whether the codestream uses reversible coding.
    pub reversible: bool,
    /// Whether a multi-component transform should be applied.
    pub use_mct: bool,
    /// JPEG 2000 guard bits used to derive total coded bitplanes.
    pub guard_bits: u8,
    /// Code-block width in samples.
    pub code_block_width: u32,
    /// Code-block height in samples.
    pub code_block_height: u32,
    /// Packet progression order to emit.
    pub progression_order: J2kPacketizationProgressionOrder,
    /// Per-component sampling factors, as `(x_rsiz, y_rsiz)`.
    pub component_sampling: &'a [(u8, u8)],
    /// Quantization step sizes, as `(exponent, mantissa)`, in codestream order.
    pub quantization_steps: &'a [(u16, u16)],
}

/// Adapter LRCP packetization code-block contribution for backend experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct J2kPacketizationCodeBlock<'a> {
    /// Encoded Tier-1 bitstream bytes for this packet contribution.
    pub data: &'a [u8],
    /// HTJ2K cleanup segment length in bytes when using high-throughput coding.
    pub ht_cleanup_length: u32,
    /// HTJ2K refinement segment length in bytes when using high-throughput coding.
    pub ht_refinement_length: u32,
    /// Number of coding passes in this contribution.
    pub num_coding_passes: u8,
    /// Number of zero most-significant bitplanes before first inclusion.
    pub num_zero_bitplanes: u8,
    /// Whether this code-block was included in a previous packet.
    pub previously_included: bool,
    /// L-block value used for segment length coding.
    pub l_block: u32,
    /// Block coder used for this contribution.
    pub block_coding_mode: J2kPacketizationBlockCodingMode,
}

/// Adapter packetization block coding mode for backend experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum J2kPacketizationBlockCodingMode {
    /// Classic JPEG 2000 Part 1 EBCOT block coding.
    Classic,
    /// High-throughput JPEG 2000 Part 15 block coding.
    HighThroughput,
}

/// Adapter packet progression order for backend packetization experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum J2kPacketizationProgressionOrder {
    /// Layer-resolution-component-position progression.
    Lrcp,
    /// Resolution-layer-component-position progression.
    Rlcp,
    /// Resolution-position-component-layer progression.
    Rpcl,
    /// Position-component-resolution-layer progression.
    Pcrl,
    /// Component-position-resolution-layer progression.
    Cprl,
}

impl J2kPacketizationProgressionOrder {
    /// Return the JPEG 2000 COD progression-order byte for this order.
    pub const fn codestream_order_code(self) -> u8 {
        match self {
            Self::Lrcp => 0x00,
            Self::Rlcp => 0x01,
            Self::Rpcl => 0x02,
            Self::Pcrl => 0x03,
            Self::Cprl => 0x04,
        }
    }
}

/// Adapter LRCP packetization subband precinct for backend experimentation.
#[derive(Debug, PartialEq, Eq)]
pub struct J2kPacketizationSubband<'a> {
    /// Code-block contributions in row-major order.
    pub code_blocks: Vec<J2kPacketizationCodeBlock<'a>>,
    /// Number of code-blocks in the x direction.
    pub num_cbs_x: u32,
    /// Number of code-blocks in the y direction.
    pub num_cbs_y: u32,
}

/// Adapter LRCP packetization resolution packet for backend experimentation.
#[derive(Debug, PartialEq, Eq)]
pub struct J2kPacketizationResolution<'a> {
    /// Subbands in packet order: LL for resolution 0, then HL/LH/HH.
    pub subbands: Vec<J2kPacketizationSubband<'a>>,
}

/// Adapter explicit packet descriptor for backend packetization experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct J2kPacketizationPacketDescriptor {
    /// Index into the packet contribution array.
    pub packet_index: u32,
    /// Persistent packet-state index for repeated layer/precinct packets.
    pub state_index: u32,
    /// Quality layer for inclusion tag-tree thresholds.
    pub layer: u8,
    /// Resolution index in the output progression.
    pub resolution: u32,
    /// Component index in the output progression.
    pub component: u16,
    /// Precinct index in the output progression.
    pub precinct: u64,
}

/// Sort explicit packet descriptors according to a JPEG 2000 progression order.
pub fn sort_packet_descriptors_for_progression(
    descriptors: &mut [J2kPacketizationPacketDescriptor],
    progression_order: J2kPacketizationProgressionOrder,
) {
    match progression_order {
        J2kPacketizationProgressionOrder::Lrcp => descriptors.sort_by_key(|descriptor| {
            (
                descriptor.layer,
                descriptor.resolution,
                descriptor.component,
                descriptor.precinct,
            )
        }),
        J2kPacketizationProgressionOrder::Rlcp => descriptors.sort_by_key(|descriptor| {
            (
                descriptor.resolution,
                descriptor.layer,
                descriptor.component,
                descriptor.precinct,
            )
        }),
        J2kPacketizationProgressionOrder::Rpcl => descriptors.sort_by_key(|descriptor| {
            (
                descriptor.resolution,
                descriptor.precinct,
                descriptor.component,
                descriptor.layer,
            )
        }),
        J2kPacketizationProgressionOrder::Pcrl => descriptors.sort_by_key(|descriptor| {
            (
                descriptor.precinct,
                descriptor.component,
                descriptor.resolution,
                descriptor.layer,
            )
        }),
        J2kPacketizationProgressionOrder::Cprl => descriptors.sort_by_key(|descriptor| {
            (
                descriptor.component,
                descriptor.precinct,
                descriptor.resolution,
                descriptor.layer,
            )
        }),
    }
}

/// Adapter LRCP packetization job for backend experimentation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct J2kPacketizationEncodeJob<'a> {
    /// Number of resolution packets prepared for packetization.
    pub resolution_count: u32,
    /// Number of layers to write.
    pub num_layers: u8,
    /// Number of image components.
    pub num_components: u16,
    /// Total number of code-block contributions.
    pub code_block_count: u32,
    /// Packet progression order to emit.
    pub progression_order: J2kPacketizationProgressionOrder,
    /// Explicit packet descriptors in output progression order.
    pub packet_descriptors: &'a [J2kPacketizationPacketDescriptor],
    /// Packet payload prepared by Tier-1, in LRCP packet order.
    pub resolutions: &'a [J2kPacketizationResolution<'a>],
}

#[cfg(test)]
mod packet_order_tests {
    use super::{
        sort_packet_descriptors_for_progression, J2kPacketizationPacketDescriptor,
        J2kPacketizationProgressionOrder,
    };

    fn descriptors() -> [J2kPacketizationPacketDescriptor; 3] {
        [
            J2kPacketizationPacketDescriptor {
                packet_index: 0,
                state_index: 0,
                layer: 1,
                resolution: 0,
                component: 2,
                precinct: 1,
            },
            J2kPacketizationPacketDescriptor {
                packet_index: 1,
                state_index: 1,
                layer: 0,
                resolution: 1,
                component: 1,
                precinct: 0,
            },
            J2kPacketizationPacketDescriptor {
                packet_index: 2,
                state_index: 2,
                layer: 0,
                resolution: 0,
                component: 0,
                precinct: 2,
            },
        ]
    }

    #[test]
    fn progression_order_codes_match_codestream_values() {
        assert_eq!(
            J2kPacketizationProgressionOrder::Lrcp.codestream_order_code(),
            0
        );
        assert_eq!(
            J2kPacketizationProgressionOrder::Rlcp.codestream_order_code(),
            1
        );
        assert_eq!(
            J2kPacketizationProgressionOrder::Rpcl.codestream_order_code(),
            2
        );
        assert_eq!(
            J2kPacketizationProgressionOrder::Pcrl.codestream_order_code(),
            3
        );
        assert_eq!(
            J2kPacketizationProgressionOrder::Cprl.codestream_order_code(),
            4
        );
    }

    #[test]
    fn packet_descriptor_sort_uses_requested_progression_order() {
        let mut lrcp = descriptors();
        sort_packet_descriptors_for_progression(&mut lrcp, J2kPacketizationProgressionOrder::Lrcp);
        assert_eq!(lrcp.map(|descriptor| descriptor.packet_index), [2, 1, 0]);

        let mut pcrl = descriptors();
        sort_packet_descriptors_for_progression(&mut pcrl, J2kPacketizationProgressionOrder::Pcrl);
        assert_eq!(pcrl.map(|descriptor| descriptor.packet_index), [1, 0, 2]);
    }
}

/// Adapter encode-stage dispatch counters for backend experimentation.
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
pub struct J2kEncodeDispatchReport {
    /// Pixel deinterleave/level-shift dispatch count.
    pub deinterleave: usize,
    /// Forward RCT kernel dispatch count.
    pub forward_rct: usize,
    /// Forward ICT kernel dispatch count.
    pub forward_ict: usize,
    /// Forward reversible 5/3 DWT kernel dispatch count.
    pub forward_dwt53: usize,
    /// Forward irreversible 9/7 DWT kernel dispatch count.
    pub forward_dwt97: usize,
    /// Sub-band quantization dispatch count.
    pub quantize_subband: usize,
    /// Tier-1 code-block encode dispatch count.
    pub tier1_code_block: usize,
    /// HTJ2K code-block encode dispatch count.
    pub ht_code_block: usize,
    /// Packetization dispatch count.
    pub packetization: usize,
}

impl J2kEncodeDispatchReport {
    /// Return the saturating per-stage delta from `before` to `self`.
    #[must_use]
    pub fn saturating_delta(self, before: Self) -> Self {
        Self {
            deinterleave: self.deinterleave.saturating_sub(before.deinterleave),
            forward_rct: self.forward_rct.saturating_sub(before.forward_rct),
            forward_ict: self.forward_ict.saturating_sub(before.forward_ict),
            forward_dwt53: self.forward_dwt53.saturating_sub(before.forward_dwt53),
            forward_dwt97: self.forward_dwt97.saturating_sub(before.forward_dwt97),
            quantize_subband: self
                .quantize_subband
                .saturating_sub(before.quantize_subband),
            tier1_code_block: self
                .tier1_code_block
                .saturating_sub(before.tier1_code_block),
            ht_code_block: self.ht_code_block.saturating_sub(before.ht_code_block),
            packetization: self.packetization.saturating_sub(before.packetization),
        }
    }

    /// Return total dispatches across all encode stages.
    #[must_use]
    pub fn total(self) -> usize {
        self.forward_rct
            .saturating_add(self.deinterleave)
            .saturating_add(self.forward_ict)
            .saturating_add(self.forward_dwt53)
            .saturating_add(self.forward_dwt97)
            .saturating_add(self.quantize_subband)
            .saturating_add(self.tier1_code_block)
            .saturating_add(self.ht_code_block)
            .saturating_add(self.packetization)
    }

    /// Return whether at least one encode stage dispatched.
    #[must_use]
    pub fn any(self) -> bool {
        self.total() > 0
    }
}

/// Adapter CPU-only encode accelerator that always falls back to native stages.
#[derive(Debug, Default, Clone, Copy)]
pub struct CpuOnlyJ2kEncodeStageAccelerator;

/// Adapter JPEG 2000 encode-stage accelerator for backend experimentation.
pub trait J2kEncodeStageAccelerator {
    /// Report cumulative backend dispatches completed by this accelerator.
    fn dispatch_report(&self) -> J2kEncodeDispatchReport {
        J2kEncodeDispatchReport::default()
    }

    /// Optionally deinterleave interleaved pixel bytes into f32 component planes.
    ///
    /// Return `Ok(Some(components))` with one plane per component. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_deinterleave(
        &mut self,
        _job: J2kDeinterleaveToF32Job<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<Vec<f32>>>> {
        Ok(None)
    }

    /// Optionally apply forward RCT in place.
    ///
    /// Return `Ok(true)` after writing transformed planes. Return `Ok(false)`
    /// to use the CPU fallback.
    fn encode_forward_rct(&mut self, _job: J2kForwardRctJob<'_>) -> J2kEncodeStageResult<bool> {
        Ok(false)
    }

    /// Optionally apply forward ICT in place.
    ///
    /// Return `Ok(true)` after writing transformed planes. Return `Ok(false)`
    /// to use the CPU fallback.
    fn encode_forward_ict(&mut self, _job: J2kForwardIctJob<'_>) -> J2kEncodeStageResult<bool> {
        Ok(false)
    }

    /// Optionally run a forward reversible 5/3 DWT.
    ///
    /// Return `Ok(Some(output))` with all subbands populated. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_forward_dwt53(
        &mut self,
        _job: J2kForwardDwt53Job<'_>,
    ) -> J2kEncodeStageResult<Option<J2kForwardDwt53Output>> {
        Ok(None)
    }

    /// Optionally run a forward irreversible 9/7 DWT.
    ///
    /// Return `Ok(Some(output))` with all subbands populated. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_forward_dwt97(
        &mut self,
        _job: J2kForwardDwt97Job<'_>,
    ) -> J2kEncodeStageResult<Option<J2kForwardDwt97Output>> {
        Ok(None)
    }

    /// Optionally quantize one sub-band.
    ///
    /// Return `Ok(Some(coefficients))` with one quantized coefficient for each
    /// input coefficient. Return `Ok(None)` to use the CPU fallback.
    fn encode_quantize_subband(
        &mut self,
        _job: J2kQuantizeSubbandJob<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<i32>>> {
        Ok(None)
    }

    /// Optionally encode one classic Tier-1 code-block.
    ///
    /// Return `Ok(Some(output))` with encoded bytes and pass metadata. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_tier1_code_block(
        &mut self,
        _job: J2kTier1CodeBlockEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<EncodedJ2kCodeBlock>> {
        Ok(None)
    }

    /// Optionally encode multiple classic Tier-1 code-blocks in one backend dispatch.
    ///
    /// Return `Ok(Some(outputs))` with one encoded output per input job. Return
    /// `Ok(None)` to use the per-block hook or CPU fallback.
    fn encode_tier1_code_blocks(
        &mut self,
        _jobs: &[J2kTier1CodeBlockEncodeJob<'_>],
    ) -> J2kEncodeStageResult<Option<Vec<EncodedJ2kCodeBlock>>> {
        Ok(None)
    }

    /// Optionally encode one HTJ2K code-block.
    ///
    /// Return `Ok(Some(output))` with encoded bytes and pass metadata. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_ht_code_block(
        &mut self,
        _job: J2kHtCodeBlockEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<EncodedHtJ2kCodeBlock>> {
        Ok(None)
    }

    /// Optionally encode multiple HTJ2K code-blocks in one backend dispatch.
    ///
    /// Return `Ok(Some(outputs))` with one encoded output per input job. Return
    /// `Ok(None)` to use the per-block hook or CPU fallback.
    fn encode_ht_code_blocks(
        &mut self,
        _jobs: &[J2kHtCodeBlockEncodeJob<'_>],
    ) -> J2kEncodeStageResult<Option<Vec<EncodedHtJ2kCodeBlock>>> {
        Ok(None)
    }

    /// Optionally quantize and encode one HTJ2K cleanup/refinement sub-band.
    ///
    /// Return `Ok(Some(outputs))` with one encoded output per code block in
    /// raster code-block order. Return `Ok(None)` to use the separate
    /// quantization and code-block hooks or CPU fallback.
    fn encode_ht_subband(
        &mut self,
        _job: J2kHtSubbandEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<EncodedHtJ2kCodeBlock>>> {
        Ok(None)
    }

    /// Optionally encode the complete HTJ2K tile packet body.
    ///
    /// Return `Ok(Some(bytes))` with the complete tile bitstream body. CPU
    /// marker/header writing remains outside this hook. Return `Ok(None)` to
    /// use the normal staged encode pipeline.
    fn encode_htj2k_tile(
        &mut self,
        _job: J2kHtj2kTileEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<u8>>> {
        Ok(None)
    }

    /// Optionally encode a complete HTJ2K tile whose pixels remain backend-resident.
    ///
    /// Unlike [`Self::encode_htj2k_tile`], this hook has no host sample slice.
    /// A resident-input facade must treat `Ok(None)` as a hard decline because
    /// there are no host pixels from which to run the CPU fallback pipeline.
    fn encode_resident_htj2k_tile(
        &mut self,
        _job: J2kResidentHtj2kTileEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<u8>>> {
        Ok(None)
    }

    /// Return whether native CPU code-block fallback should use internal rayon parallelism.
    ///
    /// External accelerators keep serial per-block fallback so their hooks still
    /// observe every fallback block after a declined batch hook.
    fn prefer_parallel_cpu_code_block_fallback(&self) -> bool {
        false
    }

    /// Return whether whole-tile CPU-only batch encode may be parallelized by callers.
    ///
    /// This is narrower than [`Self::prefer_parallel_cpu_code_block_fallback`]:
    /// callers must only bypass the supplied accelerator when it is known to
    /// have no observable hooks.
    fn prefer_parallel_cpu_tile_encode(&self) -> bool {
        false
    }

    /// Optionally packetize prepared packet contributions.
    ///
    /// Return `Ok(Some(bytes))` with the complete tile bitstream. Return
    /// `Ok(None)` to use the CPU fallback.
    fn encode_packetization(
        &mut self,
        _job: J2kPacketizationEncodeJob<'_>,
    ) -> J2kEncodeStageResult<Option<Vec<u8>>> {
        Ok(None)
    }
}

#[doc(hidden)]
impl J2kEncodeStageAccelerator for CpuOnlyJ2kEncodeStageAccelerator {
    fn prefer_parallel_cpu_code_block_fallback(&self) -> bool {
        true
    }

    fn prefer_parallel_cpu_tile_encode(&self) -> bool {
        true
    }
}

/// Multipliers applied to irreversible 9/7 quantization step sizes by subband.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct IrreversibleQuantizationSubbandScales {
    /// Multiplier for the LL subband.
    pub low_low: f32,
    /// Multiplier for HL subbands.
    pub high_low: f32,
    /// Multiplier for LH subbands.
    pub low_high: f32,
    /// Multiplier for HH subbands.
    pub high_high: f32,
}

/// Public JPEG 2000 irreversible quantization step-size tuple.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct IrreversibleQuantizationStep {
    /// Quantization step-size exponent.
    pub exponent: u8,
    /// Quantization step-size mantissa.
    pub mantissa: u16,
}

impl Default for IrreversibleQuantizationSubbandScales {
    fn default() -> Self {
        Self {
            low_low: 1.0,
            high_low: 1.0,
            low_high: 1.0,
            high_high: 1.0,
        }
    }
}

/// Precomputed reversible 5/3 wavelet coefficients for one component.
#[derive(Debug)]
pub struct PrecomputedHtj2k53Component {
    /// Horizontal SIZ sampling factor (`XRsiz`).
    pub x_rsiz: u8,
    /// Vertical SIZ sampling factor (`YRsiz`).
    pub y_rsiz: u8,
    /// Forward 5/3 DWT output, ordered as the encoder expects.
    pub dwt: J2kForwardDwt53Output,
}

/// Precomputed reversible 5/3 wavelet image.
#[derive(Debug)]
pub struct PrecomputedHtj2k53Image {
    /// Reference-grid image width.
    pub width: u32,
    /// Reference-grid image height.
    pub height: u32,
    /// Component precision in bits.
    pub bit_depth: u8,
    /// Whether component samples are signed.
    pub signed: bool,
    /// Components at their native resolution.
    pub components: Vec<PrecomputedHtj2k53Component>,
}

/// Precomputed irreversible 9/7 wavelet coefficients for one component.
#[derive(Debug)]
pub struct PrecomputedHtj2k97Component {
    /// Horizontal SIZ sampling factor (`XRsiz`).
    pub x_rsiz: u8,
    /// Vertical SIZ sampling factor (`YRsiz`).
    pub y_rsiz: u8,
    /// Forward 9/7 DWT output, ordered as the encoder expects.
    pub dwt: J2kForwardDwt97Output,
}

/// Precomputed irreversible 9/7 wavelet image.
#[derive(Debug)]
pub struct PrecomputedHtj2k97Image {
    /// Reference-grid image width.
    pub width: u32,
    /// Reference-grid image height.
    pub height: u32,
    /// Component precision in bits.
    pub bit_depth: u8,
    /// Whether component samples are signed.
    pub signed: bool,
    /// Components at their native resolution.
    pub components: Vec<PrecomputedHtj2k97Component>,
}

/// Prequantized irreversible 9/7 HTJ2K code-block image.
#[derive(Debug)]
pub struct PrequantizedHtj2k97Image {
    /// Reference-grid image width.
    pub width: u32,
    /// Reference-grid image height.
    pub height: u32,
    /// Component precision in bits.
    pub bit_depth: u8,
    /// Whether component samples are signed.
    pub signed: bool,
    /// Components at their native resolution.
    pub components: Vec<PrequantizedHtj2k97Component>,
}

/// Prequantized irreversible 9/7 HTJ2K component.
#[derive(Debug)]
pub struct PrequantizedHtj2k97Component {
    /// Horizontal SIZ sampling factor (`XRsiz`).
    pub x_rsiz: u8,
    /// Vertical SIZ sampling factor (`YRsiz`).
    pub y_rsiz: u8,
    /// Resolution packets for this component, ordered from lowest to highest.
    pub resolutions: Vec<PrequantizedHtj2k97Resolution>,
}

/// One component resolution's prequantized HTJ2K subbands.
#[derive(Debug)]
pub struct PrequantizedHtj2k97Resolution {
    /// Subbands in packet order: LL for resolution 0, then HL/LH/HH.
    pub subbands: Vec<PrequantizedHtj2k97Subband>,
}

/// One prequantized HTJ2K subband split into code-blocks.
#[derive(Debug)]
pub struct PrequantizedHtj2k97Subband {
    /// Subband kind.
    pub sub_band_type: J2kSubBandType,
    /// Number of code-blocks in the x direction.
    pub num_cbs_x: u32,
    /// Number of code-blocks in the y direction.
    pub num_cbs_y: u32,
    /// Total bitplanes declared for every code-block in this subband.
    pub total_bitplanes: u8,
    /// Code-block coefficients in row-major code-block order.
    pub code_blocks: Vec<PrequantizedHtj2k97CodeBlock>,
}

/// One prequantized HTJ2K code-block.
#[derive(Debug)]
pub struct PrequantizedHtj2k97CodeBlock {
    /// Quantized coefficients in row-major order.
    pub coefficients: Vec<i32>,
    /// Code-block width in coefficients.
    pub width: u32,
    /// Code-block height in coefficients.
    pub height: u32,
}

/// Preencoded irreversible 9/7 HTJ2K code-block image.
#[derive(Debug)]
pub struct PreencodedHtj2k97Image {
    /// Reference-grid image width.
    pub width: u32,
    /// Reference-grid image height.
    pub height: u32,
    /// Component precision in bits.
    pub bit_depth: u8,
    /// Whether component samples are signed.
    pub signed: bool,
    /// Components at their native resolution.
    pub components: Vec<PreencodedHtj2k97Component>,
}

/// Preencoded irreversible 9/7 HTJ2K component.
#[derive(Debug)]
pub struct PreencodedHtj2k97Component {
    /// Horizontal SIZ sampling factor (`XRsiz`).
    pub x_rsiz: u8,
    /// Vertical SIZ sampling factor (`YRsiz`).
    pub y_rsiz: u8,
    /// Resolution packets for this component, ordered from lowest to highest.
    pub resolutions: Vec<PreencodedHtj2k97Resolution>,
}

/// One component resolution's preencoded HTJ2K subbands.
#[derive(Debug)]
pub struct PreencodedHtj2k97Resolution {
    /// Subbands in packet order: LL for resolution 0, then HL/LH/HH.
    pub subbands: Vec<PreencodedHtj2k97Subband>,
}

/// One preencoded HTJ2K subband split into code-blocks.
#[derive(Debug)]
pub struct PreencodedHtj2k97Subband {
    /// Subband kind.
    pub sub_band_type: J2kSubBandType,
    /// Number of code-blocks in the x direction.
    pub num_cbs_x: u32,
    /// Number of code-blocks in the y direction.
    pub num_cbs_y: u32,
    /// Total bitplanes declared for every code-block in this subband.
    pub total_bitplanes: u8,
    /// Encoded code-block payloads in row-major code-block order.
    pub code_blocks: Vec<PreencodedHtj2k97CodeBlock>,
}

/// One preencoded HTJ2K code-block.
#[derive(Debug)]
pub struct PreencodedHtj2k97CodeBlock {
    /// Code-block width in coefficients.
    pub width: u32,
    /// Code-block height in coefficients.
    pub height: u32,
    /// Encoded cleanup/refinement payload and packet metadata.
    pub encoded: EncodedHtJ2kCodeBlock,
}

/// Preencoded irreversible 9/7 HTJ2K code-block image backed by one compact
/// payload buffer.
#[derive(Debug)]
pub struct PreencodedHtj2k97CompactImage {
    /// Reference-grid image width.
    pub width: u32,
    /// Reference-grid image height.
    pub height: u32,
    /// Component precision in bits.
    pub bit_depth: u8,
    /// Whether component samples are signed.
    pub signed: bool,
    /// Contiguous encoded code-block payload bytes.
    pub payload: Vec<u8>,
    /// Components at their native resolution.
    pub components: Vec<PreencodedHtj2k97CompactComponent>,
}

/// Preencoded compact irreversible 9/7 HTJ2K component.
#[derive(Debug)]
pub struct PreencodedHtj2k97CompactComponent {
    /// Horizontal SIZ sampling factor (`XRsiz`).
    pub x_rsiz: u8,
    /// Vertical SIZ sampling factor (`YRsiz`).
    pub y_rsiz: u8,
    /// Resolution packets for this component, ordered from lowest to highest.
    pub resolutions: Vec<PreencodedHtj2k97CompactResolution>,
}

/// One component resolution's compact preencoded HTJ2K subbands.
#[derive(Debug)]
pub struct PreencodedHtj2k97CompactResolution {
    /// Subbands in packet order: LL for resolution 0, then HL/LH/HH.
    pub subbands: Vec<PreencodedHtj2k97CompactSubband>,
}

/// One compact preencoded HTJ2K subband split into code-blocks.
#[derive(Debug)]
pub struct PreencodedHtj2k97CompactSubband {
    /// Subband kind.
    pub sub_band_type: J2kSubBandType,
    /// Number of code-blocks in the x direction.
    pub num_cbs_x: u32,
    /// Number of code-blocks in the y direction.
    pub num_cbs_y: u32,
    /// Total bitplanes declared for every code-block in this subband.
    pub total_bitplanes: u8,
    /// Code-block metadata in row-major code-block order.
    pub code_blocks: Vec<PreencodedHtj2k97CompactCodeBlock>,
}

/// One compact preencoded HTJ2K code-block.
#[derive(Debug)]
pub struct PreencodedHtj2k97CompactCodeBlock {
    /// Code-block width in coefficients.
    pub width: u32,
    /// Code-block height in coefficients.
    pub height: u32,
    /// Byte range into the image-level compact payload.
    pub payload_range: Range<usize>,
    /// HTJ2K cleanup segment length in bytes.
    pub cleanup_length: u32,
    /// HTJ2K refinement segment length in bytes.
    pub refinement_length: u32,
    /// Number of coding passes in the encoded payload.
    pub num_coding_passes: u8,
    /// Number of missing most-significant bitplanes.
    pub num_zero_bitplanes: u8,
}