webpkit 0.1.0

//! VP8 vocabulary and constant tables (layer 0: usable everywhere).
//!
//! Every table here is transcribed verbatim from the libwebp reference decoder
//! (`src/dec/tree_dec.c`, `src/dec/quant_dec.c`, `src/dec/vp8_dec.c`) which is
//! itself RFC 6386. Keeping them in one place lets the bitstream and pixel
//! layers share exact constants and lets a reviewer diff them against the spec.
#![allow(
    clippy::unreadable_literal,
    reason = "these are fixed spec tables transcribed verbatim from RFC 6386 / \
              libwebp; digit grouping would obscure the diff against the source"
)]

/// An 8-bit probability that a coded boolean is zero, i.e. `prob / 256`, exactly
/// as VP8 stores and transmits it.
pub(crate) type Prob = u8;

// Structural counts (libwebp `common_dec.h`).
/// Number of macroblock segments.
pub(crate) const NUM_MB_SEGMENTS: usize = 4;
/// Number of probabilities in the segment-id decision tree.
pub(crate) const MB_FEATURE_TREE_PROBS: usize = 3;
/// Number of reference-frame loop-filter deltas.
pub(crate) const NUM_REF_LF_DELTAS: usize = 4;
/// Number of prediction-mode loop-filter deltas.
pub(crate) const NUM_MODE_LF_DELTAS: usize = 4;
/// Coefficient plane types: 0 i16-AC, 1 i16-DC, 2 chroma, 3 i4-AC.
pub(crate) const NUM_TYPES: usize = 4;
/// Coefficient bands.
pub(crate) const NUM_BANDS: usize = 8;
/// Coefficient contexts (from the neighbors' non-zero state).
pub(crate) const NUM_CTX: usize = 3;
/// Probabilities per (type, band, context) node.
pub(crate) const NUM_PROBAS: usize = 11;
/// Number of intra 4×4 (B) prediction modes.
pub(crate) const NUM_BMODES: usize = 10;

// Intra 4×4 (B) prediction modes.
/// 4×4 DC prediction.
pub(crate) const B_DC_PRED: u8 = 0;
/// 4×4 `TrueMotion` prediction.
pub(crate) const B_TM_PRED: u8 = 1;
/// 4×4 vertical prediction.
pub(crate) const B_VE_PRED: u8 = 2;
/// 4×4 horizontal prediction.
pub(crate) const B_HE_PRED: u8 = 3;
/// 4×4 right-down diagonal prediction.
pub(crate) const B_RD_PRED: u8 = 4;
/// 4×4 vertical-right diagonal prediction.
pub(crate) const B_VR_PRED: u8 = 5;
/// 4×4 left-down diagonal prediction.
pub(crate) const B_LD_PRED: u8 = 6;
/// 4×4 vertical-left diagonal prediction.
pub(crate) const B_VL_PRED: u8 = 7;
/// 4×4 horizontal-down diagonal prediction.
pub(crate) const B_HD_PRED: u8 = 8;
/// 4×4 horizontal-up diagonal prediction.
pub(crate) const B_HU_PRED: u8 = 9;

// Luma-16 and chroma modes reuse the low B-mode numbers.
/// Whole-block DC prediction.
pub(crate) const DC_PRED: u8 = 0;
/// Whole-block `TrueMotion` prediction.
pub(crate) const TM_PRED: u8 = 1;
/// Whole-block vertical prediction.
pub(crate) const V_PRED: u8 = 2;
/// Whole-block horizontal prediction.
pub(crate) const H_PRED: u8 = 3;

/// The full `[type][band][context][proba]` coefficient-probability table.
pub(crate) type CoeffProbas = [[[[Prob; NUM_PROBAS]; NUM_CTX]; NUM_BANDS]; NUM_TYPES];

/// Observed token statistics per node: `[type][band][context][proba] ->
/// [count_bit0, count_bit1]`. The encoder's count pass fills this from the actual
/// quantized tokens to drive `prob_opt::optimize_probas`.
pub(crate) type CoeffStats = [[[[[u64; 2]; NUM_PROBAS]; NUM_CTX]; NUM_BANDS]; NUM_TYPES];

/// Per-node flags marking which coefficient probabilities carry a transmitted
/// update in the bitstream — the encoder's inverse of the read flags in
/// `header::parse_proba`.
pub(crate) type CoeffUpdateFlags = [[[[bool; NUM_PROBAS]; NUM_CTX]; NUM_BANDS]; NUM_TYPES];

/// Coefficient position → band mapping, with a sentinel 17th entry (RFC §13.3,
/// libwebp `kBands`).
pub(crate) const BANDS: [usize; 17] = [
    0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7, //
    0, // extra entry as sentinel
];

/// Natural → zig-zag coefficient order (RFC §13.3, libwebp `kZigzag`).
pub(crate) const ZIGZAG: [usize; 16] = [0, 1, 4, 8, 5, 2, 3, 6, 9, 12, 13, 10, 7, 11, 14, 15];

/// Extra-bit probabilities for the DCT-value categories 3–6 (RFC §13.2,
/// libwebp `kCat3`/`kCat4`/`kCat5`/`kCat6`, minus the trailing `0` sentinel).
pub(crate) const CAT_3456: [&[Prob]; 4] = [
    &[173, 148, 140],
    &[176, 155, 140, 135],
    &[180, 157, 141, 134, 130],
    &[254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129],
];

/// DC dequantization table indexed by quantizer (RFC §14.1, libwebp `kDcTable`).
pub(crate) const DC_TABLE: [u16; 128] = [
    4, 5, 6, 7, 8, 9, 10, 10, 11, 12, 13, 14, 15, 16, 17, 17, //
    18, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 25, 25, 26, 27, 28, //
    29, 30, 31, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, 43, //
    44, 45, 46, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, //
    59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, //
    75, 76, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, //
    91, 93, 95, 96, 98, 100, 101, 102, 104, 106, 108, 110, 112, 114, 116, 118, //
    122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 143, 145, 148, 151, 154, 157, //
];

/// AC dequantization table indexed by quantizer (RFC §14.1, libwebp `kAcTable`).
pub(crate) const AC_TABLE: [u16; 128] = [
    4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, //
    20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, //
    36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, //
    52, 53, 54, 55, 56, 57, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, //
    78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, //
    110, 112, 114, 116, 119, 122, 125, 128, 131, 134, 137, 140, 143, 146, 149, 152, //
    155, 158, 161, 164, 167, 170, 173, 177, 181, 185, 189, 193, 197, 201, 205, 209, //
    213, 217, 221, 225, 229, 234, 239, 245, 249, 254, 259, 264, 269, 274, 279, 284, //
];

/// Quality (`0..=100`) → base quantizer index (`0..=127`), a non-linear mapping
/// with finer control at high quality (the counterpart of libwebp's
/// `QualityToCompression` baseline). Derived offline as
/// `clamp(round(127·(1 − ∛linear_c)), 0, 127)` where
/// `linear_c = q<0.75 ? q·2/3 : 2q−1` (`q = quality/100`); only the integer
/// results are committed, so the crate stays float-free. Monotonically
/// non-increasing, with `q0 → 127` and `q100 → 0`.
pub(crate) const QUALITY_TO_BASE_Q: [u8; 101] = [
    127, 103, 97, 93, 89, 86, 84, 81, 79, 77, //
    76, 74, 72, 71, 69, 68, 67, 66, 64, 63, //
    62, 61, 60, 59, 58, 57, 56, 55, 54, 54, //
    53, 52, 51, 50, 50, 49, 48, 47, 47, 46, //
    45, 45, 44, 43, 43, 42, 41, 41, 40, 40, //
    39, 38, 38, 37, 37, 36, 36, 35, 34, 34, //
    33, 33, 32, 32, 31, 31, 30, 30, 29, 29, //
    28, 28, 28, 27, 27, 26, 25, 24, 22, 21, //
    20, 19, 18, 16, 15, 14, 13, 12, 11, 10, //
    9, 8, 7, 6, 5, 4, 3, 3, 2, 1, //
    0,
];

/// The B-mode (intra 4×4) prediction-mode probabilities, indexed by the top and
/// left neighbors' modes (RFC §11.5, libwebp `kBModesProba`).
pub(crate) const BMODES_PROBA: [[[Prob; NUM_BMODES - 1]; NUM_BMODES]; NUM_BMODES] = [
    [
        [231, 120, 48, 89, 115, 113, 120, 152, 112],
        [152, 179, 64, 126, 170, 118, 46, 70, 95],
        [175, 69, 143, 80, 85, 82, 72, 155, 103],
        [56, 58, 10, 171, 218, 189, 17, 13, 152],
        [114, 26, 17, 163, 44, 195, 21, 10, 173],
        [121, 24, 80, 195, 26, 62, 44, 64, 85],
        [144, 71, 10, 38, 171, 213, 144, 34, 26],
        [170, 46, 55, 19, 136, 160, 33, 206, 71],
        [63, 20, 8, 114, 114, 208, 12, 9, 226],
        [81, 40, 11, 96, 182, 84, 29, 16, 36],
    ],
    [
        [134, 183, 89, 137, 98, 101, 106, 165, 148],
        [72, 187, 100, 130, 157, 111, 32, 75, 80],
        [66, 102, 167, 99, 74, 62, 40, 234, 128],
        [41, 53, 9, 178, 241, 141, 26, 8, 107],
        [74, 43, 26, 146, 73, 166, 49, 23, 157],
        [65, 38, 105, 160, 51, 52, 31, 115, 128],
        [104, 79, 12, 27, 217, 255, 87, 17, 7],
        [87, 68, 71, 44, 114, 51, 15, 186, 23],
        [47, 41, 14, 110, 182, 183, 21, 17, 194],
        [66, 45, 25, 102, 197, 189, 23, 18, 22],
    ],
    [
        [88, 88, 147, 150, 42, 46, 45, 196, 205],
        [43, 97, 183, 117, 85, 38, 35, 179, 61],
        [39, 53, 200, 87, 26, 21, 43, 232, 171],
        [56, 34, 51, 104, 114, 102, 29, 93, 77],
        [39, 28, 85, 171, 58, 165, 90, 98, 64],
        [34, 22, 116, 206, 23, 34, 43, 166, 73],
        [107, 54, 32, 26, 51, 1, 81, 43, 31],
        [68, 25, 106, 22, 64, 171, 36, 225, 114],
        [34, 19, 21, 102, 132, 188, 16, 76, 124],
        [62, 18, 78, 95, 85, 57, 50, 48, 51],
    ],
    [
        [193, 101, 35, 159, 215, 111, 89, 46, 111],
        [60, 148, 31, 172, 219, 228, 21, 18, 111],
        [112, 113, 77, 85, 179, 255, 38, 120, 114],
        [40, 42, 1, 196, 245, 209, 10, 25, 109],
        [88, 43, 29, 140, 166, 213, 37, 43, 154],
        [61, 63, 30, 155, 67, 45, 68, 1, 209],
        [100, 80, 8, 43, 154, 1, 51, 26, 71],
        [142, 78, 78, 16, 255, 128, 34, 197, 171],
        [41, 40, 5, 102, 211, 183, 4, 1, 221],
        [51, 50, 17, 168, 209, 192, 23, 25, 82],
    ],
    [
        [138, 31, 36, 171, 27, 166, 38, 44, 229],
        [67, 87, 58, 169, 82, 115, 26, 59, 179],
        [63, 59, 90, 180, 59, 166, 93, 73, 154],
        [40, 40, 21, 116, 143, 209, 34, 39, 175],
        [47, 15, 16, 183, 34, 223, 49, 45, 183],
        [46, 17, 33, 183, 6, 98, 15, 32, 183],
        [57, 46, 22, 24, 128, 1, 54, 17, 37],
        [65, 32, 73, 115, 28, 128, 23, 128, 205],
        [40, 3, 9, 115, 51, 192, 18, 6, 223],
        [87, 37, 9, 115, 59, 77, 64, 21, 47],
    ],
    [
        [104, 55, 44, 218, 9, 54, 53, 130, 226],
        [64, 90, 70, 205, 40, 41, 23, 26, 57],
        [54, 57, 112, 184, 5, 41, 38, 166, 213],
        [30, 34, 26, 133, 152, 116, 10, 32, 134],
        [39, 19, 53, 221, 26, 114, 32, 73, 255],
        [31, 9, 65, 234, 2, 15, 1, 118, 73],
        [75, 32, 12, 51, 192, 255, 160, 43, 51],
        [88, 31, 35, 67, 102, 85, 55, 186, 85],
        [56, 21, 23, 111, 59, 205, 45, 37, 192],
        [55, 38, 70, 124, 73, 102, 1, 34, 98],
    ],
    [
        [125, 98, 42, 88, 104, 85, 117, 175, 82],
        [95, 84, 53, 89, 128, 100, 113, 101, 45],
        [75, 79, 123, 47, 51, 128, 81, 171, 1],
        [57, 17, 5, 71, 102, 57, 53, 41, 49],
        [38, 33, 13, 121, 57, 73, 26, 1, 85],
        [41, 10, 67, 138, 77, 110, 90, 47, 114],
        [115, 21, 2, 10, 102, 255, 166, 23, 6],
        [101, 29, 16, 10, 85, 128, 101, 196, 26],
        [57, 18, 10, 102, 102, 213, 34, 20, 43],
        [117, 20, 15, 36, 163, 128, 68, 1, 26],
    ],
    [
        [102, 61, 71, 37, 34, 53, 31, 243, 192],
        [69, 60, 71, 38, 73, 119, 28, 222, 37],
        [68, 45, 128, 34, 1, 47, 11, 245, 171],
        [62, 17, 19, 70, 146, 85, 55, 62, 70],
        [37, 43, 37, 154, 100, 163, 85, 160, 1],
        [63, 9, 92, 136, 28, 64, 32, 201, 85],
        [75, 15, 9, 9, 64, 255, 184, 119, 16],
        [86, 6, 28, 5, 64, 255, 25, 248, 1],
        [56, 8, 17, 132, 137, 255, 55, 116, 128],
        [58, 15, 20, 82, 135, 57, 26, 121, 40],
    ],
    [
        [164, 50, 31, 137, 154, 133, 25, 35, 218],
        [51, 103, 44, 131, 131, 123, 31, 6, 158],
        [86, 40, 64, 135, 148, 224, 45, 183, 128],
        [22, 26, 17, 131, 240, 154, 14, 1, 209],
        [45, 16, 21, 91, 64, 222, 7, 1, 197],
        [56, 21, 39, 155, 60, 138, 23, 102, 213],
        [83, 12, 13, 54, 192, 255, 68, 47, 28],
        [85, 26, 85, 85, 128, 128, 32, 146, 171],
        [18, 11, 7, 63, 144, 171, 4, 4, 246],
        [35, 27, 10, 146, 174, 171, 12, 26, 128],
    ],
    [
        [190, 80, 35, 99, 180, 80, 126, 54, 45],
        [85, 126, 47, 87, 176, 51, 41, 20, 32],
        [101, 75, 128, 139, 118, 146, 116, 128, 85],
        [56, 41, 15, 176, 236, 85, 37, 9, 62],
        [71, 30, 17, 119, 118, 255, 17, 18, 138],
        [101, 38, 60, 138, 55, 70, 43, 26, 142],
        [146, 36, 19, 30, 171, 255, 97, 27, 20],
        [138, 45, 61, 62, 219, 1, 81, 188, 64],
        [32, 41, 20, 117, 151, 142, 20, 21, 163],
        [112, 19, 12, 61, 195, 128, 48, 4, 24],
    ],
];

/// Default coefficient probabilities before any bitstream update (RFC §13.5,
/// libwebp `CoeffsProba0`).
pub(crate) const COEFFS_PROBA_0: CoeffProbas = [
    [
        [
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
        [
            [253, 136, 254, 255, 228, 219, 128, 128, 128, 128, 128],
            [189, 129, 242, 255, 227, 213, 255, 219, 128, 128, 128],
            [106, 126, 227, 252, 214, 209, 255, 255, 128, 128, 128],
        ],
        [
            [1, 98, 248, 255, 236, 226, 255, 255, 128, 128, 128],
            [181, 133, 238, 254, 221, 234, 255, 154, 128, 128, 128],
            [78, 134, 202, 247, 198, 180, 255, 219, 128, 128, 128],
        ],
        [
            [1, 185, 249, 255, 243, 255, 128, 128, 128, 128, 128],
            [184, 150, 247, 255, 236, 224, 128, 128, 128, 128, 128],
            [77, 110, 216, 255, 236, 230, 128, 128, 128, 128, 128],
        ],
        [
            [1, 101, 251, 255, 241, 255, 128, 128, 128, 128, 128],
            [170, 139, 241, 252, 236, 209, 255, 255, 128, 128, 128],
            [37, 116, 196, 243, 228, 255, 255, 255, 128, 128, 128],
        ],
        [
            [1, 204, 254, 255, 245, 255, 128, 128, 128, 128, 128],
            [207, 160, 250, 255, 238, 128, 128, 128, 128, 128, 128],
            [102, 103, 231, 255, 211, 171, 128, 128, 128, 128, 128],
        ],
        [
            [1, 152, 252, 255, 240, 255, 128, 128, 128, 128, 128],
            [177, 135, 243, 255, 234, 225, 128, 128, 128, 128, 128],
            [80, 129, 211, 255, 194, 224, 128, 128, 128, 128, 128],
        ],
        [
            [1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [246, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [255, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
    ],
    [
        [
            [198, 35, 237, 223, 193, 187, 162, 160, 145, 155, 62],
            [131, 45, 198, 221, 172, 176, 220, 157, 252, 221, 1],
            [68, 47, 146, 208, 149, 167, 221, 162, 255, 223, 128],
        ],
        [
            [1, 149, 241, 255, 221, 224, 255, 255, 128, 128, 128],
            [184, 141, 234, 253, 222, 220, 255, 199, 128, 128, 128],
            [81, 99, 181, 242, 176, 190, 249, 202, 255, 255, 128],
        ],
        [
            [1, 129, 232, 253, 214, 197, 242, 196, 255, 255, 128],
            [99, 121, 210, 250, 201, 198, 255, 202, 128, 128, 128],
            [23, 91, 163, 242, 170, 187, 247, 210, 255, 255, 128],
        ],
        [
            [1, 200, 246, 255, 234, 255, 128, 128, 128, 128, 128],
            [109, 178, 241, 255, 231, 245, 255, 255, 128, 128, 128],
            [44, 130, 201, 253, 205, 192, 255, 255, 128, 128, 128],
        ],
        [
            [1, 132, 239, 251, 219, 209, 255, 165, 128, 128, 128],
            [94, 136, 225, 251, 218, 190, 255, 255, 128, 128, 128],
            [22, 100, 174, 245, 186, 161, 255, 199, 128, 128, 128],
        ],
        [
            [1, 182, 249, 255, 232, 235, 128, 128, 128, 128, 128],
            [124, 143, 241, 255, 227, 234, 128, 128, 128, 128, 128],
            [35, 77, 181, 251, 193, 211, 255, 205, 128, 128, 128],
        ],
        [
            [1, 157, 247, 255, 236, 231, 255, 255, 128, 128, 128],
            [121, 141, 235, 255, 225, 227, 255, 255, 128, 128, 128],
            [45, 99, 188, 251, 195, 217, 255, 224, 128, 128, 128],
        ],
        [
            [1, 1, 251, 255, 213, 255, 128, 128, 128, 128, 128],
            [203, 1, 248, 255, 255, 128, 128, 128, 128, 128, 128],
            [137, 1, 177, 255, 224, 255, 128, 128, 128, 128, 128],
        ],
    ],
    [
        [
            [253, 9, 248, 251, 207, 208, 255, 192, 128, 128, 128],
            [175, 13, 224, 243, 193, 185, 249, 198, 255, 255, 128],
            [73, 17, 171, 221, 161, 179, 236, 167, 255, 234, 128],
        ],
        [
            [1, 95, 247, 253, 212, 183, 255, 255, 128, 128, 128],
            [239, 90, 244, 250, 211, 209, 255, 255, 128, 128, 128],
            [155, 77, 195, 248, 188, 195, 255, 255, 128, 128, 128],
        ],
        [
            [1, 24, 239, 251, 218, 219, 255, 205, 128, 128, 128],
            [201, 51, 219, 255, 196, 186, 128, 128, 128, 128, 128],
            [69, 46, 190, 239, 201, 218, 255, 228, 128, 128, 128],
        ],
        [
            [1, 191, 251, 255, 255, 128, 128, 128, 128, 128, 128],
            [223, 165, 249, 255, 213, 255, 128, 128, 128, 128, 128],
            [141, 124, 248, 255, 255, 128, 128, 128, 128, 128, 128],
        ],
        [
            [1, 16, 248, 255, 255, 128, 128, 128, 128, 128, 128],
            [190, 36, 230, 255, 236, 255, 128, 128, 128, 128, 128],
            [149, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
        [
            [1, 226, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [247, 192, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [240, 128, 255, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
        [
            [1, 134, 252, 255, 255, 128, 128, 128, 128, 128, 128],
            [213, 62, 250, 255, 255, 128, 128, 128, 128, 128, 128],
            [55, 93, 255, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
        [
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
            [128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
    ],
    [
        [
            [202, 24, 213, 235, 186, 191, 220, 160, 240, 175, 255],
            [126, 38, 182, 232, 169, 184, 228, 174, 255, 187, 128],
            [61, 46, 138, 219, 151, 178, 240, 170, 255, 216, 128],
        ],
        [
            [1, 112, 230, 250, 199, 191, 247, 159, 255, 255, 128],
            [166, 109, 228, 252, 211, 215, 255, 174, 128, 128, 128],
            [39, 77, 162, 232, 172, 180, 245, 178, 255, 255, 128],
        ],
        [
            [1, 52, 220, 246, 198, 199, 249, 220, 255, 255, 128],
            [124, 74, 191, 243, 183, 193, 250, 221, 255, 255, 128],
            [24, 71, 130, 219, 154, 170, 243, 182, 255, 255, 128],
        ],
        [
            [1, 182, 225, 249, 219, 240, 255, 224, 128, 128, 128],
            [149, 150, 226, 252, 216, 205, 255, 171, 128, 128, 128],
            [28, 108, 170, 242, 183, 194, 254, 223, 255, 255, 128],
        ],
        [
            [1, 81, 230, 252, 204, 203, 255, 192, 128, 128, 128],
            [123, 102, 209, 247, 188, 196, 255, 233, 128, 128, 128],
            [20, 95, 153, 243, 164, 173, 255, 203, 128, 128, 128],
        ],
        [
            [1, 222, 248, 255, 216, 213, 128, 128, 128, 128, 128],
            [168, 175, 246, 252, 235, 205, 255, 255, 128, 128, 128],
            [47, 116, 215, 255, 211, 212, 255, 255, 128, 128, 128],
        ],
        [
            [1, 121, 236, 253, 212, 214, 255, 255, 128, 128, 128],
            [141, 84, 213, 252, 201, 202, 255, 219, 128, 128, 128],
            [42, 80, 160, 240, 162, 185, 255, 205, 128, 128, 128],
        ],
        [
            [1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [244, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
            [238, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128],
        ],
    ],
];

/// Fixed-point bit cost of coding a boolean at probability `p / 256`, indexed by
/// `p` in `0..=256`: `round(256 * -log2(p / 256))` in 1/256-bit units (so
/// `[256] == 0`, `[128] == 256`, `[1] == 2048`; index `0` is an unused `65535`
/// sentinel). Transcribed from libwebp `VP8EntropyCost` (`src/enc/cost_enc.c`); it
/// lets the coefficient-probability optimizer weigh a transmitted update against
/// its coding saving with integer arithmetic only.
pub(crate) const ENTROPY_COST: [u16; 257] = [
    65535, 2048, 1792, 1642, 1536, 1454, 1386, 1329, 1280, 1236, 1198, 1162, 1130, 1101, 1073,
    1048, 1024, 1002, 980, 961, 942, 924, 906, 890, 874, 859, 845, 831, 817, 804, 792, 780, 768,
    757, 746, 735, 724, 714, 705, 695, 686, 676, 668, 659, 650, 642, 634, 626, 618, 611, 603, 596,
    589, 582, 575, 568, 561, 555, 548, 542, 536, 530, 524, 518, 512, 506, 501, 495, 490, 484, 479,
    474, 468, 463, 458, 453, 449, 444, 439, 434, 430, 425, 420, 416, 412, 407, 403, 399, 394, 390,
    386, 382, 378, 374, 370, 366, 362, 358, 355, 351, 347, 343, 340, 336, 333, 329, 326, 322, 319,
    315, 312, 309, 305, 302, 299, 296, 292, 289, 286, 283, 280, 277, 274, 271, 268, 265, 262, 259,
    256, 253, 250, 247, 245, 242, 239, 236, 234, 231, 228, 226, 223, 220, 218, 215, 212, 210, 207,
    205, 202, 200, 197, 195, 193, 190, 188, 185, 183, 181, 178, 176, 174, 171, 169, 167, 164, 162,
    160, 158, 156, 153, 151, 149, 147, 145, 143, 140, 138, 136, 134, 132, 130, 128, 126, 124, 122,
    120, 118, 116, 114, 112, 110, 108, 106, 104, 102, 101, 99, 97, 95, 93, 91, 89, 87, 86, 84, 82,
    80, 78, 77, 75, 73, 71, 70, 68, 66, 64, 63, 61, 59, 58, 56, 54, 53, 51, 49, 48, 46, 44, 43, 41,
    40, 38, 36, 35, 33, 32, 30, 28, 27, 25, 24, 22, 21, 19, 18, 16, 15, 13, 12, 10, 9, 7, 6, 4, 3,
    1, 0,
];

/// Probabilities for whether each coefficient probability is updated in the
/// bitstream (RFC §13.4, libwebp `CoeffsUpdateProba`).
pub(crate) const COEFFS_UPDATE_PROBA: CoeffProbas = [
    [
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [176, 246, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [223, 241, 252, 255, 255, 255, 255, 255, 255, 255, 255],
            [249, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 244, 252, 255, 255, 255, 255, 255, 255, 255, 255],
            [234, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 246, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [239, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [251, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [251, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 253, 255, 254, 255, 255, 255, 255, 255, 255],
            [250, 255, 254, 255, 254, 255, 255, 255, 255, 255, 255],
            [254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
    ],
    [
        [
            [217, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [225, 252, 241, 253, 255, 255, 254, 255, 255, 255, 255],
            [234, 250, 241, 250, 253, 255, 253, 254, 255, 255, 255],
        ],
        [
            [255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [223, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [238, 253, 254, 254, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [249, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 253, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [247, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [252, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
    ],
    [
        [
            [186, 251, 250, 255, 255, 255, 255, 255, 255, 255, 255],
            [234, 251, 244, 254, 255, 255, 255, 255, 255, 255, 255],
            [251, 251, 243, 253, 254, 255, 254, 255, 255, 255, 255],
        ],
        [
            [255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [236, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [251, 253, 253, 254, 254, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
    ],
    [
        [
            [248, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [250, 254, 252, 254, 255, 255, 255, 255, 255, 255, 255],
            [248, 254, 249, 253, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [246, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [252, 254, 251, 254, 254, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 254, 252, 255, 255, 255, 255, 255, 255, 255, 255],
            [248, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [253, 255, 254, 254, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [245, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [253, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 251, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [252, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 252, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [249, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 253, 255, 255, 255, 255, 255, 255, 255, 255],
            [250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
        [
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
            [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255],
        ],
    ],
];