/* Copyright 2017 Google Inc. All Rights Reserved.

   Distributed under MIT license.

   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT

*/

#include "compound_dictionary.h"

#include "../common/platform.h"

#include <brotli/shared_dictionary.h>

#include "memory.h"

static PreparedDictionary* CreatePreparedDictionaryWithParams(MemoryManager* m,

    const uint8_t* source, size_t source_size, uint32_t bucket_bits,

    uint32_t slot_bits, uint32_t hash_bits, uint16_t bucket_limit) {

  /* Step 1: create "bloated" hasher. */

  uint32_t num_slots = 1u << slot_bits;

  uint32_t num_buckets = 1u << bucket_bits;

  uint32_t hash_shift = 64u - bucket_bits;

  uint64_t hash_mask = (~((uint64_t)0U)) >> (64 - hash_bits);

  uint32_t slot_mask = num_slots - 1;

  size_t alloc_size = (sizeof(uint32_t) << slot_bits) +

      (sizeof(uint32_t) << slot_bits) +

      (sizeof(uint16_t) << bucket_bits) +

      (sizeof(uint32_t) << bucket_bits) +

      (sizeof(uint32_t) * source_size);

  uint8_t* flat = NULL;

  PreparedDictionary* result = NULL;

  uint16_t* num = NULL;

  uint32_t* bucket_heads = NULL;

  uint32_t* next_bucket = NULL;

  uint32_t* slot_offsets = NULL;

  uint16_t* heads = NULL;

  uint32_t* items = NULL;

  uint8_t** source_ref = NULL;

  uint32_t i;

  uint32_t* slot_size = NULL;

  uint32_t* slot_limit = NULL;

  uint32_t total_items = 0;

  if (slot_bits > 16) return NULL;

  if (slot_bits > bucket_bits) return NULL;

  if (bucket_bits - slot_bits >= 16) return NULL;

  flat = BROTLI_ALLOC(m, uint8_t, alloc_size);

  if (BROTLI_IS_OOM(m) || BROTLI_IS_NULL(flat)) return NULL;

  slot_size = (uint32_t*)flat;

  slot_limit = (uint32_t*)(&slot_size[num_slots]);

  num = (uint16_t*)(&slot_limit[num_slots]);

  bucket_heads = (uint32_t*)(&num[num_buckets]);

  next_bucket = (uint32_t*)(&bucket_heads[num_buckets]);

  memset(num, 0, num_buckets * sizeof(num[0]));

  /* TODO(eustas): apply custom "store" order. */

  for (i = 0; i + 7 < source_size; ++i) {

    const uint64_t h = (BROTLI_UNALIGNED_LOAD64LE(&source[i]) & hash_mask) *

        kPreparedDictionaryHashMul64Long;

    const uint32_t key = (uint32_t)(h >> hash_shift);

    uint16_t count = num[key];

    next_bucket[i] = (count == 0) ? ((uint32_t)(-1)) : bucket_heads[key];

    bucket_heads[key] = i;

    count++;

    if (count > bucket_limit) count = bucket_limit;

    num[key] = count;

  }

  /* Step 2: find slot limits. */

  for (i = 0; i < num_slots; ++i) {

    BROTLI_BOOL overflow = BROTLI_FALSE;

    slot_limit[i] = bucket_limit;

    while (BROTLI_TRUE) {

      uint32_t limit = slot_limit[i];

      size_t j;

      uint32_t count = 0;

      overflow = BROTLI_FALSE;

      for (j = i; j < num_buckets; j += num_slots) {

        uint32_t size = num[j];

        /* Last chain may span behind 64K limit; overflow happens only if

           we are about to use 0xFFFF+ as item offset. */

        if (count >= 0xFFFF) {

          overflow = BROTLI_TRUE;

          break;

        }

        if (size > limit) size = limit;

        count += size;

      }

      if (!overflow) {

        slot_size[i] = count;

        total_items += count;

        break;

      }

      slot_limit[i]--;

    }

  }

  /* Step 3: transfer data to "slim" hasher. */

  alloc_size = sizeof(PreparedDictionary) + (sizeof(uint32_t) << slot_bits) +

      (sizeof(uint16_t) << bucket_bits) + (sizeof(uint32_t) * total_items) +

      sizeof(uint8_t*);

  result = (PreparedDictionary*)BROTLI_ALLOC(m, uint8_t, alloc_size);

  if (BROTLI_IS_OOM(m) || BROTLI_IS_NULL(result)) {

    BROTLI_FREE(m, flat);

    return NULL;

  }

  slot_offsets = (uint32_t*)(&result[1]);

  heads = (uint16_t*)(&slot_offsets[num_slots]);

  items = (uint32_t*)(&heads[num_buckets]);

  source_ref = (uint8_t**)(&items[total_items]);

  result->magic = kLeanPreparedDictionaryMagic;

  result->num_items = total_items;

  result->source_size = (uint32_t)source_size;

  result->hash_bits = hash_bits;

  result->bucket_bits = bucket_bits;

  result->slot_bits = slot_bits;

  BROTLI_UNALIGNED_STORE_PTR(source_ref, source);

  total_items = 0;

  for (i = 0; i < num_slots; ++i) {

    slot_offsets[i] = total_items;

    total_items += slot_size[i];

    slot_size[i] = 0;

  }

  for (i = 0; i < num_buckets; ++i) {

    uint32_t slot = i & slot_mask;

    uint32_t count = num[i];

    uint32_t pos;

    size_t j;

    size_t cursor = slot_size[slot];

    if (count > slot_limit[slot]) count = slot_limit[slot];

    if (count == 0) {

      heads[i] = 0xFFFF;

      continue;

    }

    heads[i] = (uint16_t)cursor;

    cursor += slot_offsets[slot];

    slot_size[slot] += count;

    pos = bucket_heads[i];

    for (j = 0; j < count; j++) {

      items[cursor++] = pos;

      pos = next_bucket[pos];

    }

    items[cursor - 1] |= 0x80000000;

  }

  BROTLI_FREE(m, flat);

  return result;

}

PreparedDictionary* CreatePreparedDictionary(MemoryManager* m,

    const uint8_t* source, size_t source_size) {

  uint32_t bucket_bits = 17;

  uint32_t slot_bits = 7;

  uint32_t hash_bits = 40;

  uint16_t bucket_limit = 32;

  size_t volume = 16u << bucket_bits;

  /* Tune parameters to fit dictionary size. */

  while (volume < source_size && bucket_bits < 22) {

    bucket_bits++;

    slot_bits++;

    volume <<= 1;

  }

  return CreatePreparedDictionaryWithParams(m,

      source, source_size, bucket_bits, slot_bits, hash_bits, bucket_limit);

}

void DestroyPreparedDictionary(MemoryManager* m,

    PreparedDictionary* dictionary) {

  if (!dictionary) return;

  BROTLI_FREE(m, dictionary);

}

BROTLI_BOOL AttachPreparedDictionary(

    CompoundDictionary* compound, const PreparedDictionary* dictionary) {

  size_t length = 0;

  size_t index = 0;

  if (compound->num_chunks == SHARED_BROTLI_MAX_COMPOUND_DICTS) {

    return BROTLI_FALSE;

  }

  if (!dictionary) return BROTLI_FALSE;

  length = dictionary->source_size;

  index = compound->num_chunks;

  compound->total_size += length;

  compound->chunks[index] = dictionary;

  compound->chunk_offsets[index + 1] = compound->total_size;

  {

    uint32_t* slot_offsets = (uint32_t*)(&dictionary[1]);

    uint16_t* heads = (uint16_t*)(&slot_offsets[(size_t)1u << dictionary->slot_bits]);

    uint32_t* items = (uint32_t*)(&heads[(size_t)1u << dictionary->bucket_bits]);

    const void* tail = (void*)&items[dictionary->num_items];

    if (dictionary->magic == kPreparedDictionaryMagic) {

      compound->chunk_source[index] = (const uint8_t*)tail;

    } else {

      /* dictionary->magic == kLeanPreparedDictionaryMagic */

      compound->chunk_source[index] =

          (const uint8_t*)BROTLI_UNALIGNED_LOAD_PTR((const uint8_t**)tail);

    }

  }

  compound->num_chunks++;

  return BROTLI_TRUE;

}