cmp_varlen_keys.h

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#ifndef CMP_VARLEN_KEYS_INCLUDED
#define CMP_VARLEN_KEYS_INCLUDED

#include <assert.h>
#include <stdio.h>
#include <functional>

#include "sql/sort_param.h"
#include "sql/sql_array.h"

/**
  A compare function for variable-length keys used by filesort().
  For record format documentation, @see Sort_param.

  @param  sort_field_array array of field descriptors for sorting
  @param  use_hash compare hash values (for grouping of JSON data)
  @param  s1 pointer to record 1
  @param  s2 pointer to record 2
  @return true/false according to sorting order
          true  : s1 < s2
          false : s1 >= s2
 */
inline bool cmp_varlen_keys(
    Bounds_checked_array<st_sort_field> sort_field_array, bool use_hash,
    const uchar *s1, const uchar *s2) {
  const uchar *kp1 = s1 + Sort_param::size_of_varlength_field;
  const uchar *kp2 = s2 + Sort_param::size_of_varlength_field;
  int res;
  for (const st_sort_field &sort_field : sort_field_array) {
    uint kp1_len, kp2_len, kp_len;
    if (sort_field.maybe_null) {
      const int k1_nullbyte = *kp1++;
      const int k2_nullbyte = *kp2++;
      if (k1_nullbyte != k2_nullbyte) return k1_nullbyte < k2_nullbyte;
      if (k1_nullbyte == 0 || k1_nullbyte == 0xff) {
        if (!sort_field.is_varlen) {
          kp1 += sort_field.length;
          kp2 += sort_field.length;
        }
        continue;  // Both key parts are null, nothing to compare
      }
    }
    if (sort_field.is_varlen) {
      assert(uint4korr(kp1) >= 4);
      assert(uint4korr(kp2) >= 4);

      kp1_len = uint4korr(kp1) - 4;
      kp1 += 4;

      kp2_len = uint4korr(kp2) - 4;
      kp2 += 4;

      kp_len = std::min(kp1_len, kp2_len);
    } else {
      kp_len = kp1_len = kp2_len = sort_field.length;
    }

    res = memcmp(kp1, kp2, kp_len);

    if (res) return res < 0;
    if (kp1_len != kp2_len) {
      if (sort_field.reverse)
        return kp2_len < kp1_len;
      else
        return kp1_len < kp2_len;
    }

    kp1 += kp1_len;
    kp2 += kp2_len;
  }

  if (use_hash) {
    // Compare hashes at the end of sort keys
    return memcmp(kp1, kp2, 8) < 0;
  } else {
    return false;
  }
}

/**
  This struct is used for merging chunks for filesort()
  For filesort() with fixed-size keys we use memcmp to compare rows.
  For variable length keys, we use cmp_varlen_keys to compare rows.
 */
struct Merge_chunk_greater {
  size_t m_len;
  Sort_param *m_param;

  // CTOR for filesort() with fixed-size keys
  explicit Merge_chunk_greater(size_t len) : m_len(len), m_param(nullptr) {}

  // CTOR for filesort() with varlen keys
  explicit Merge_chunk_greater(Sort_param *param) : m_len(0), m_param(param) {}

  bool operator()(Merge_chunk *a, Merge_chunk *b) const {
    return key_is_greater_than(a->current_key(), b->current_key());
  }

  bool key_is_greater_than(uchar *key1, uchar *key2) const {
    // Fixed len keys
    if (m_len) return memcmp(key1, key2, m_len) > 0;

    if (m_param)
      return cmp_varlen_keys(m_param->local_sortorder, m_param->use_hash, key2,
                             key1);

    // We can actually have zero-length sort key for filesort().
    return false;
  }
};

#endif  // CMP_VARLEN_KEYS_INCLUDED