// SPDX-License-Identifier: Apache-2.0

// ----------------------------------------------------------------------------

// Copyright 2011-2026 Arm Limited

//

// Licensed under the Apache License, Version 2.0 (the "License"); you may not

// use this file except in compliance with the License. You may obtain a copy

// of the License at:

//

//     http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT

// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the

// License for the specific language governing permissions and limitations

// under the License.

// ----------------------------------------------------------------------------

/**

 * @brief Functions for generating partition tables on demand.

 */

#include "astcenc_internal.h"

/** @brief The number of 64-bit words needed to represent a canonical partition bit pattern. */

#define BIT_PATTERN_WORDS (((ASTCENC_BLOCK_MAX_TEXELS * 2) + 63) / 64)

/**

 * @brief Generate a canonical representation of a partition pattern.

 *

 * The returned value stores two bits per texel, for up to 6x6x6 texels, where the two bits store

 * the remapped texel index. Remapping ensures that we only match on the partition pattern,

 * independent of the partition order generated by the hash.

 *

 * @param      texel_count          The number of texels in the block.

 * @param      partition_of_texel   The partition assignments, in hash order.

 * @param[out] bit_pattern          The output bit pattern representation.

 */

static void generate_canonical_partitioning(

  unsigned int texel_count,

  const uint8_t* partition_of_texel,

  uint64_t bit_pattern[BIT_PATTERN_WORDS]

) {

  // Clear the pattern

  for (unsigned int i = 0; i < BIT_PATTERN_WORDS; i++)

  {

    bit_pattern[i] = 0;

  }

  // Store a mapping to reorder the raw partitions so that the partitions are ordered such

  // that the lowest texel index in partition N is smaller than the lowest texel index in

  // partition N + 1.

  int mapped_index[BLOCK_MAX_PARTITIONS];

  int map_weight_count = 0;

  for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONS; i++)

  {

    mapped_index[i] = -1;

  }

  for (unsigned int i = 0; i < texel_count; i++)

  {

    int index = partition_of_texel[i];

    if (mapped_index[index] < 0)

    {

      mapped_index[index] = map_weight_count++;

    }

    uint64_t xlat_index = mapped_index[index];

    bit_pattern[i >> 5] |= xlat_index << (2 * (i & 0x1F));

  }

}

/**

 * @brief Compare two canonical patterns to see if they are the same.

 *

 * @param part1   The first canonical bit pattern to check.

 * @param part2   The second canonical bit pattern to check.

 *

 * @return @c true if the patterns are the same, @c false otherwise.

 */

static bool compare_canonical_partitionings(

  const uint64_t part1[BIT_PATTERN_WORDS],

  const uint64_t part2[BIT_PATTERN_WORDS]

) {

  return (part1[0] == part2[0])

#if BIT_PATTERN_WORDS > 1

      && (part1[1] == part2[1])

#endif

#if BIT_PATTERN_WORDS > 2

      && (part1[2] == part2[2])

#endif

#if BIT_PATTERN_WORDS > 3

      && (part1[3] == part2[3])

#endif

#if BIT_PATTERN_WORDS > 4

      && (part1[4] == part2[4])

#endif

#if BIT_PATTERN_WORDS > 5

      && (part1[5] == part2[5])

#endif

#if BIT_PATTERN_WORDS > 6

      && (part1[6] == part2[6])

#endif

      ;

}

/**

 * @brief Hash function used for procedural partition assignment.

 *

 * @param inp   The hash seed.

 *

 * @return The hashed value.

 */

static uint32_t hash52(

  uint32_t inp

) {

  inp ^= inp >> 15;

  // (2^4 + 1) * (2^7 + 1) * (2^17 - 1)

  inp *= 0xEEDE0891;

  inp ^= inp >> 5;

  inp += inp << 16;

  inp ^= inp >> 7;

  inp ^= inp >> 3;

  inp ^= inp << 6;

  inp ^= inp >> 17;

  return inp;

}

/**

 * @brief Select texel assignment for a single coordinate.

 *

 * @param seed              The seed - the partition index from the block.

 * @param x                 The texel X coordinate in the block.

 * @param y                 The texel Y coordinate in the block.

 * @param z                 The texel Z coordinate in the block.

 * @param partition_count   The total partition count of this encoding.

 * @param small_block       @c true if the block has fewer than 32 texels.

 *

 * @return The assigned partition index for this texel.

 */

static uint8_t select_partition(

  int seed,

  int x,

  int y,

  int z,

  int partition_count,

  bool small_block

) {

  // For small blocks bias the coordinates to get better distribution

  if (small_block)

  {

    x <<= 1;

    y <<= 1;

    z <<= 1;

  }

  seed += (partition_count - 1) * 1024;

  uint32_t rnum = hash52(seed);

  uint8_t seed1 = rnum & 0xF;

  uint8_t seed2 = (rnum >> 4) & 0xF;

  uint8_t seed3 = (rnum >> 8) & 0xF;

  uint8_t seed4 = (rnum >> 12) & 0xF;

  uint8_t seed5 = (rnum >> 16) & 0xF;

  uint8_t seed6 = (rnum >> 20) & 0xF;

  uint8_t seed7 = (rnum >> 24) & 0xF;

  uint8_t seed8 = (rnum >> 28) & 0xF;

  uint8_t seed9 = (rnum >> 18) & 0xF;

  uint8_t seed10 = (rnum >> 22) & 0xF;

  uint8_t seed11 = (rnum >> 26) & 0xF;

  uint8_t seed12 = ((rnum >> 30) | (rnum << 2)) & 0xF;

  // Squaring all the seeds in order to bias their distribution towards lower values.

  seed1 *= seed1;

  seed2 *= seed2;

  seed3 *= seed3;

  seed4 *= seed4;

  seed5 *= seed5;

  seed6 *= seed6;

  seed7 *= seed7;

  seed8 *= seed8;

  seed9 *= seed9;

  seed10 *= seed10;

  seed11 *= seed11;

  seed12 *= seed12;

  int sh1, sh2;

  if (seed & 1)

  {

    sh1 = (seed & 2 ? 4 : 5);

    sh2 = (partition_count == 3 ? 6 : 5);

  }

  else

  {

    sh1 = (partition_count == 3 ? 6 : 5);

    sh2 = (seed & 2 ? 4 : 5);

  }

  int sh3 = (seed & 0x10) ? sh1 : sh2;

  seed1 >>= sh1;

  seed2 >>= sh2;

  seed3 >>= sh1;

  seed4 >>= sh2;

  seed5 >>= sh1;

  seed6 >>= sh2;

  seed7 >>= sh1;

  seed8 >>= sh2;

  seed9 >>= sh3;

  seed10 >>= sh3;

  seed11 >>= sh3;

  seed12 >>= sh3;

  int a = seed1 * x + seed2 * y + seed11 * z + (rnum >> 14);

  int b = seed3 * x + seed4 * y + seed12 * z + (rnum >> 10);

  int c = seed5 * x + seed6 * y + seed9 * z + (rnum >> 6);

  int d = seed7 * x + seed8 * y + seed10 * z + (rnum >> 2);

  // Apply the saw

  a &= 0x3F;

  b &= 0x3F;

  c &= 0x3F;

  d &= 0x3F;

  // Remove some of the components if we are to output < 4 partitions.

  if (partition_count <= 3)

  {

    d = 0;

  }

  if (partition_count <= 2)

  {

    c = 0;

  }

  if (partition_count <= 1)

  {

    b = 0;

  }

  uint8_t partition;

  if (a >= b && a >= c && a >= d)

  {

    partition = 0;

  }

  else if (b >= c && b >= d)

  {

    partition = 1;

  }

  else if (c >= d)

  {

    partition = 2;

  }

  else

  {

    partition = 3;

  }

  return partition;

}

/**

 * @brief Generate a single partition info structure.

 *

 * @param[out] bsd                     The block size information.

 * @param      partition_count         The partition count of this partitioning.

 * @param      partition_index         The partition index / seed of this partitioning.

 * @param      partition_remap_index   The remapped partition index of this partitioning.

 * @param[out] pi                      The partition info structure to populate.

 *

 * @return True if this is a useful partition index, False if we can skip it.

 */

static bool generate_one_partition_info_entry(

  block_size_descriptor& bsd,

  unsigned int partition_count,

  unsigned int partition_index,

  unsigned int partition_remap_index,

  partition_info& pi

) {

#if defined(ASTCENC_DECOMPRESS_ONLY)

  // Suppress unused parameter warning

  (void)partition_remap_index;

#endif

  int texels_per_block = bsd.texel_count;

  bool small_block = texels_per_block < 32;

  uint8_t *partition_of_texel = pi.partition_of_texel;

  // Assign texels to partitions

  int texel_idx = 0;

  int counts[BLOCK_MAX_PARTITIONS] { 0 };

  for (unsigned int z = 0; z < bsd.dim_z; z++)

  {

    for (unsigned int y = 0; y <  bsd.dim_y; y++)

    {

      for (unsigned int x = 0; x <  bsd.dim_x; x++)

      {

        uint8_t part = select_partition(partition_index, x, y, z, partition_count, small_block);

        pi.texels_of_partition[part][counts[part]++] = static_cast<uint8_t>(texel_idx++);

        *partition_of_texel++ = part;

      }

    }

  }

  // Fill loop tail so we can overfetch later

  for (unsigned int i = 0; i < partition_count; i++)

  {

    size_t ptex_count = counts[i];

    size_t ptex_count_simd = round_up_to_simd_multiple_vla(ptex_count);

    for (size_t j = ptex_count; j < ptex_count_simd; j++)

    {

      pi.texels_of_partition[i][j] = pi.texels_of_partition[i][ptex_count - 1];

    }

  }

  // Populate the actual procedural partition count

  if (counts[0] == 0)

  {

    pi.partition_count = 0;

  }

  else if (counts[1] == 0)

  {

    pi.partition_count = 1;

  }

  else if (counts[2] == 0)

  {

    pi.partition_count = 2;

  }

  else if (counts[3] == 0)

  {

    pi.partition_count = 3;

  }

  else

  {

    pi.partition_count = 4;

  }

  // Populate the partition index

  pi.partition_index = static_cast<uint16_t>(partition_index);

  for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONS; i++)

  {

    pi.partition_texel_count[i] = static_cast<uint8_t>(counts[i]);

  }

  // Valid partitionings have texels in all of the requested partitions

  bool valid = pi.partition_count == partition_count;

#if !defined(ASTCENC_DECOMPRESS_ONLY)

  // Populate the coverage bitmaps for 2/3/4 partitions

  uint64_t* bitmaps { nullptr };

  if (partition_count == 2)

  {

    bitmaps = bsd.coverage_bitmaps_2[partition_remap_index];

  }

  else if (partition_count == 3)

  {

    bitmaps = bsd.coverage_bitmaps_3[partition_remap_index];

  }

  else if (partition_count == 4)

  {

    bitmaps = bsd.coverage_bitmaps_4[partition_remap_index];

  }

  if (bitmaps)

  {

    // Populate the partition coverage bitmap

    for (unsigned int i = 0; i < partition_count; i++)

    {

      bitmaps[i] = 0ULL;

    }

    unsigned int texels_to_process = astc::min(bsd.texel_count, BLOCK_MAX_KMEANS_TEXELS);

    for (unsigned int i = 0; i < texels_to_process; i++)

    {

      unsigned int idx = bsd.kmeans_texels[i];

      bitmaps[pi.partition_of_texel[idx]] |= 1ULL << i;

    }

  }

#endif

  return valid;

}

static void build_partition_table_for_one_partition_count(

  block_size_descriptor& bsd,

  bool can_omit_partitionings,

  unsigned int partition_count_cutoff,

  unsigned int partition_count,

  partition_info* ptab,

  uint64_t* canonical_patterns

) {

  unsigned int next_index = 0;

  bsd.partitioning_count_selected[partition_count - 1] = 0;

  bsd.partitioning_count_all[partition_count - 1] = 0;

  // Mark all partitionings as unused; the loops below overwrite the entries

  // that are actually kept. Partitionings dropped in self-decompress mode

  // must retain this known-bad value so that decoding an unknown raw

  // partition index does not result in a bad packed index.

  for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONINGS; i++)

  {

    bsd.partitioning_packed_index[partition_count - 2][i] = BLOCK_BAD_PARTITIONING;

  }

  // Skip tables larger than config max partition count if we can omit modes

  if (can_omit_partitionings && (partition_count > partition_count_cutoff))

  {

    return;

  }

  // Iterate through twice

  //   - Pass 0: Keep selected partitionings

  //   - Pass 1: Keep non-selected partitionings (skip if in omit mode)

  unsigned int max_iter = can_omit_partitionings ? 1 : 2;

  // Tracker for things we built in the first iteration

  uint8_t build[BLOCK_MAX_PARTITIONINGS] { 0 };

  for (unsigned int x = 0; x < max_iter; x++)

  {

    for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONINGS; i++)

    {

      // Don't include things we built in the first pass

      if ((x == 1) && build[i])

      {

        continue;

      }

      bool keep_useful = generate_one_partition_info_entry(bsd, partition_count, i, next_index, ptab[next_index]);

      if ((x == 0) && !keep_useful)

      {

        continue;

      }

      generate_canonical_partitioning(bsd.texel_count, ptab[next_index].partition_of_texel, canonical_patterns + next_index * BIT_PATTERN_WORDS);

      bool keep_canonical = true;

      for (unsigned int j = 0; j < next_index; j++)

      {

        bool match = compare_canonical_partitionings(canonical_patterns + next_index * BIT_PATTERN_WORDS, canonical_patterns +  j * BIT_PATTERN_WORDS);

        if (match)

        {

          keep_canonical = false;

          break;

        }

      }

      if (keep_useful && keep_canonical)

      {

        if (x == 0)

        {

          bsd.partitioning_packed_index[partition_count - 2][i] = static_cast<uint16_t>(next_index);

          bsd.partitioning_count_selected[partition_count - 1]++;

          bsd.partitioning_count_all[partition_count - 1]++;

          build[i] = 1;

          next_index++;

        }

      }

      else

      {

        if (x == 1)

        {

          bsd.partitioning_packed_index[partition_count - 2][i] = static_cast<uint16_t>(next_index);

          bsd.partitioning_count_all[partition_count - 1]++;

          next_index++;

        }

      }

    }

  }

}

/* See header for documentation. */

void init_partition_tables(

  block_size_descriptor& bsd,

  bool can_omit_partitionings,

  unsigned int partition_count_cutoff

) {

  partition_info* par_tab2 = bsd.partitionings;

  partition_info* par_tab3 = par_tab2 + BLOCK_MAX_PARTITIONINGS;

  partition_info* par_tab4 = par_tab3 + BLOCK_MAX_PARTITIONINGS;

  partition_info* par_tab1 = par_tab4 + BLOCK_MAX_PARTITIONINGS;

  generate_one_partition_info_entry(bsd, 1, 0, 0, *par_tab1);

  bsd.partitioning_count_selected[0] = 1;

  bsd.partitioning_count_all[0] = 1;

  uint64_t* canonical_patterns = new uint64_t[BLOCK_MAX_PARTITIONINGS * BIT_PATTERN_WORDS];

  build_partition_table_for_one_partition_count(bsd, can_omit_partitionings, partition_count_cutoff, 2, par_tab2, canonical_patterns);

  build_partition_table_for_one_partition_count(bsd, can_omit_partitionings, partition_count_cutoff, 3, par_tab3, canonical_patterns);

  build_partition_table_for_one_partition_count(bsd, can_omit_partitionings, partition_count_cutoff, 4, par_tab4, canonical_patterns);

  delete[] canonical_patterns;

}