cell_calculator.h

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/* Copyright (c) 2018, 2024, Oracle and/or its affiliates.
 
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the terms of the GNU General Public License, version 2.0, as published by the
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/** @file storage/temptable/include/temptable/cell_calculator.h
TempTable Cell_calculator declaration. */
 
#ifndef TEMPTABLE_CELL_CALCULATOR_H
#define TEMPTABLE_CELL_CALCULATOR_H
 
#include <algorithm>
#include <cstdint>
 
#include "my_dbug.h"
#include "my_murmur3.h"
#include "mysql/strings/m_ctype.h"
#include "sql/field.h"
#include "sql/key.h"
#include "storage/temptable/include/temptable/cell.h"
 
namespace temptable {
 
/** Utility to perform calculations for a cell. It uses cell's contents and
a stored context that describes how to interpret the data. */
class Cell_calculator {
 public:
  /** Default constructor used for std::array initialization in Index. */
  Cell_calculator() = default;
 
  /** Constructor to be used when creating calculators for indexed columns. */
  explicit Cell_calculator(
      /** [in] Key part (indexed column) for which calculator is created. */
      const KEY_PART_INFO &mysql_key_part);
 
  /** Constructor to be used when creating calculators for columns when
  comparing table rows. */
  explicit Cell_calculator(
      /** [in] Field (column) for which calculator is created. */
      const Field *mysql_field);
 
  /** Calculate hash value for a cell.
   * @return a hash number */
  size_t hash(
      /** [in] Cell for which hash is to be calculated. */
      const Cell &cell) const;
 
  /** Compare two cells.
   * @retval <0 if lhs < rhs
   * @retval  0 if lhs == rhs
   * @retval >0 if lhs > rhs */
  int compare(
      /** [in] First cell to compare. */
      const Cell &lhs,
      /** [in] Second cell to compare. */
      const Cell &rhs) const;
 
 private:
  enum class Mode : uint8_t {
    BINARY,
    CHARSET,
    CHARSET_AND_CHAR_LENGTH,
  };
 
  static const CHARSET_INFO *field_charset(const Field &field);
 
  /** Field for which this calculator was created. */
  const Field *m_mysql_field;
 
  /** Charset used by calculator. NULL for binary mode. */
  const CHARSET_INFO *m_cs;
 
  /** Calculation mode. */
  Mode m_mode;
 
  /** True if the key is of type double or float */
  bool m_is_floating_point;
 
  /** True if the cell is right-padded with spaces (CHAR column). */
  bool m_is_space_padded;
 
  /** Length in number of characters.
   * Only used in CHARSET_AND_CHAR_LENGTH mode. */
  uint32_t m_char_length;
 
  /** This value is to be used for hashing 0 value for approximate types such as
   * float or double. Specifically, for such types we don't want to have
   * separate hash entries for 0.0 and -0.0. */
  static const size_t s_zero_hash;
  static size_t zero_hash();
};
 
/* Implementation of inlined methods. */
 
inline Cell_calculator::Cell_calculator(const KEY_PART_INFO &mysql_key_part)
    : m_mysql_field(mysql_key_part.field),
      m_cs(field_charset(*m_mysql_field)),
      m_is_floating_point(m_mysql_field->key_type() == HA_KEYTYPE_FLOAT ||
                          m_mysql_field->key_type() == HA_KEYTYPE_DOUBLE),
      m_is_space_padded(m_mysql_field->key_type() == HA_KEYTYPE_TEXT),
      m_char_length(0) {
  /* Mimic hp_hashnr() from storage/heap/hp_hash.c. */
 
  if (m_cs != nullptr) {
    /* Decide if we should use my_charpos. */
    bool use_char_length = (m_cs->mbmaxlen > 1) &&
                           (mysql_key_part.key_part_flag & HA_PART_KEY_SEG);
 
    DBUG_EXECUTE_IF("temptable_use_char_length", use_char_length = true;);
 
    if (use_char_length) {
      m_char_length = mysql_key_part.length / m_cs->mbmaxlen;
      m_mode = Mode::CHARSET_AND_CHAR_LENGTH;
    } else {
      m_mode = Mode::CHARSET;
    }
  } else {
    m_mode = Mode::BINARY;
  }
}
 
inline Cell_calculator::Cell_calculator(const Field *mysql_field)
    : m_mysql_field(mysql_field),
      m_cs(field_charset(*m_mysql_field)),
      m_is_floating_point(m_mysql_field->key_type() == HA_KEYTYPE_FLOAT ||
                          m_mysql_field->key_type() == HA_KEYTYPE_DOUBLE),
      m_is_space_padded(m_mysql_field->key_type() == HA_KEYTYPE_TEXT),
      m_char_length(0) {
  /* Mimic hp_hashnr() from storage/heap/hp_hash.c. */
 
  /* No partial keys, so no CHARSET_AND_CHAR_LENGTH here. */
 
  if (m_cs != nullptr) {
    m_mode = Mode::CHARSET;
  } else {
    m_mode = Mode::BINARY;
  }
}
 
inline const CHARSET_INFO *Cell_calculator::field_charset(const Field &field) {
  /* Decide if we should use charset+collation for comparisons, or rely on pure
   * binary data. */
  switch (field.key_type()) {
    case HA_KEYTYPE_TEXT:
    case HA_KEYTYPE_VARTEXT1:
    case HA_KEYTYPE_VARTEXT2:
    case HA_KEYTYPE_VARBINARY1:
    case HA_KEYTYPE_VARBINARY2:
      if (field.is_flag_set(ENUM_FLAG) || field.is_flag_set(SET_FLAG)) {
        return &my_charset_bin;
      } else {
        return field.charset_for_protocol();
      }
    default:
      return nullptr;
  }
}
 
inline size_t Cell_calculator::hash(const Cell &cell) const {
  if (cell.is_null()) {
    return 1;
  }
 
  auto data_length = cell.data_length();
  auto data = cell.data();
 
  /* For approximate types, 0.0 and -0.0 may have different bit patterns. Treat
   * all such patterns as belonging to a single value. */
  if (m_is_floating_point) {
    assert(data_length == 4 || data_length == 8);
    const double val = data_length == 4 ? float4get(data) : float8get(data);
    if (val == 0.0) return s_zero_hash;
    return murmur3_32(data, data_length, 0);
  }
 
  /*
   * If the collation of field to calculate hash is with PAD_SPACE attribute,
   * empty string '' and space ' ' will be calculated as different hash values,
   * because we handle empty string '' directly (return 0), and calculate hash
   * with cs for space ' '. But actually, for collations with PAD_SPACE
   * attribute empty string '' should be equal with space ' '. Do not return
   * hash value 0 if data_length == 0. */
 
  size_t length = 0;
 
  /*
  switch (m_mode) {
    case Mode::CHARSET:
      length = ...
      break;
    case Mode::CHARSET_AND_CHAR_LENGTH:
      length = ...
      break;
    case Mode::BINARY:
      return ...
  }
  code <-- this is executed when
  indexed_column.cell_hash_function() == Mode::BINARY
  and compiled with "Studio 12.5 Sun C++ 5.14 SunOS_sparc 2016/05/31" !!!
  So we use if-else instead of switch below. */
 
  if (m_mode == Mode::BINARY) {
    return murmur3_32(data, data_length, 0);
  } else if (m_mode == Mode::CHARSET) {
    length = data_length;
  } else if (m_mode == Mode::CHARSET_AND_CHAR_LENGTH) {
    length =
        std::min(static_cast<size_t>(data_length),
                 my_charpos(m_cs, data, data + data_length, m_char_length));
  } else {
    my_abort();
  }
 
  /* If the field is space padded but collation do not want to use
   * the padding it is required to strip the spaces from the end. */
  if (m_is_space_padded && (m_cs->pad_attribute == NO_PAD)) {
    length = m_cs->cset->lengthsp(m_cs, reinterpret_cast<const char *>(data),
                                  length);
  }
 
  uint64 h1 = 1;
  uint64 h2 = 4;
  m_cs->coll->hash_sort(m_cs, data, length, &h1, &h2);
  return h1;
}
 
inline int Cell_calculator::compare(const Cell &lhs, const Cell &rhs) const {
  if (lhs.is_null()) {
    if (rhs.is_null()) {
      /* Both are NULL. */
      return 0;
    } else {
      /* NULL < whatever (not NULL). */
      return -1;
    }
  } else {
    if (rhs.is_null()) {
      /* whatever (not NULL) > NULL. */
      return 1;
    }
  }
 
  /* Both cells are not NULL. */
  auto lhs_data_length = lhs.data_length();
  auto rhs_data_length = rhs.data_length();
 
  /* If both cells' data is identical, then no need to use the expensive
   * comparisons below because we know that they will report equality. */
  if ((lhs_data_length == rhs_data_length) &&
      ((lhs_data_length == 0) ||
       (memcmp(lhs.data(), rhs.data(), lhs_data_length) == 0))) {
    return 0;
  }
 
  auto lhs_data = lhs.data();
  auto rhs_data = rhs.data();
 
  size_t lhs_length = 0;
  size_t rhs_length = 0;
 
  /* Note: Using if-s instead of switch due to bug mentioned in hash(). */
 
  if (m_mode == Mode::BINARY) {
    return const_cast<Field *>(m_mysql_field)->key_cmp(lhs_data, rhs_data);
  } else if (m_mode == Mode::CHARSET) {
    lhs_length = lhs_data_length;
    rhs_length = rhs_data_length;
  } else if (m_mode == Mode::CHARSET_AND_CHAR_LENGTH) {
    lhs_length = std::min(
        static_cast<size_t>(lhs_data_length),
        my_charpos(m_cs, lhs_data, lhs_data + lhs_data_length, m_char_length));
    rhs_length = std::min(
        static_cast<size_t>(rhs_data_length),
        my_charpos(m_cs, rhs_data, rhs_data + rhs_data_length, m_char_length));
  } else {
    my_abort();
  }
 
  /* If the field is space padded but collation do not want to use
   * the padding it is required to strip the spaces from the end. */
  if (m_is_space_padded && (m_cs->pad_attribute == NO_PAD)) {
    /* Strip trailing spaces. */
    lhs_length = m_cs->cset->lengthsp(
        m_cs, reinterpret_cast<const char *>(lhs_data), lhs_length);
    rhs_length = m_cs->cset->lengthsp(
        m_cs, reinterpret_cast<const char *>(rhs_data), rhs_length);
  }
 
  return m_cs->coll->strnncollsp(m_cs, lhs_data, lhs_length, rhs_data,
                                 rhs_length);
}
 
/**
   Convenience function to get the hash value of 0.0.
*/
inline size_t Cell_calculator::zero_hash() {
  // It's ok to have a common hash value for both 0.0 of type float and 0.0 of
  // type double. Use (double)0.0 for the same.
  uchar float_data[8];
 
  float8store(float_data, 0.0);
  return murmur3_32(float_data, 8, 0);
}
 
} /* namespace temptable */
 
#endif /* TEMPTABLE_CELL_CALCULATOR_H */