polardbxengine/storage/innobase/mach/mach0data.cc

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/** @file mach/mach0data.cc
 Utilities for converting data from the database file
 to the machine format.

 Created 11/28/1995 Heikki Tuuri
 ***********************************************************************/

#include "mach0data.h"

#include <stddef.h>

/** Read a 64-bit integer in a much compressed form.
@param[in,out]	ptr	pointer to memory where to read,
advanced by the number of bytes consumed, or set NULL if out of space
@param[in]	end_ptr	end of the buffer
@return unsigned 64-bit integer
@see mach_u64_read_much_compressed() */
ib_uint64_t mach_parse_u64_much_compressed(const byte **ptr,
                                           const byte *end_ptr) {
  ulint val;

  if (*ptr >= end_ptr) {
    *ptr = NULL;
    return (0);
  }

  val = mach_read_from_1(*ptr);

  if (val != 0xFF) {
    return (mach_parse_compressed(ptr, end_ptr));
  }

  ++*ptr;

  ib_uint64_t n = mach_parse_compressed(ptr, end_ptr);
  if (*ptr == NULL) {
    return (0);
  }

  n <<= 32;

  n |= mach_parse_compressed(ptr, end_ptr);
  if (*ptr == NULL) {
    return (0);
  }

  return (n);
}

/** Read a 32-bit integer in a compressed form.
@param[in,out]	ptr	pointer to memory where to read;
advanced by the number of bytes consumed, or set NULL if out of space
@param[in]	end_ptr	end of the buffer
@return unsigned value */
ib_uint32_t mach_parse_compressed(const byte **ptr, const byte *end_ptr) {
  ulint val;

  if (*ptr >= end_ptr) {
    *ptr = NULL;
    return (0);
  }

  val = mach_read_from_1(*ptr);

  if (val < 0x80) {
    /* 0nnnnnnn (7 bits) */
    ++*ptr;
    return (static_cast<ib_uint32_t>(val));
  }

  /* Workaround GCC bug
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77673:
  the compiler moves mach_read_from_4 right to the beginning of the
  function, causing and out-of-bounds read if we are reading a short
  integer close to the end of buffer. */
#if defined(__GNUC__) && (__GNUC__ >= 5) && !defined(__clang__)
#define DEPLOY_FENCE
#endif

#ifdef DEPLOY_FENCE
  __atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

  if (val < 0xC0) {
    /* 10nnnnnn nnnnnnnn (14 bits) */
    if (end_ptr >= *ptr + 2) {
      val = mach_read_from_2(*ptr) & 0x3FFF;
      ut_ad(val > 0x7F);
      *ptr += 2;
      return (static_cast<ib_uint32_t>(val));
    }
    *ptr = NULL;
    return (0);
  }

#ifdef DEPLOY_FENCE
  __atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

  if (val < 0xE0) {
    /* 110nnnnn nnnnnnnn nnnnnnnn (21 bits) */
    if (end_ptr >= *ptr + 3) {
      val = mach_read_from_3(*ptr) & 0x1FFFFF;
      ut_ad(val > 0x3FFF);
      *ptr += 3;
      return (static_cast<ib_uint32_t>(val));
    }
    *ptr = NULL;
    return (0);
  }

#ifdef DEPLOY_FENCE
  __atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

  if (val < 0xF0) {
    /* 1110nnnn nnnnnnnn nnnnnnnn nnnnnnnn (28 bits) */
    if (end_ptr >= *ptr + 4) {
      val = mach_read_from_4(*ptr) & 0xFFFFFFF;
      ut_ad(val > 0x1FFFFF);
      *ptr += 4;
      return (static_cast<ib_uint32_t>(val));
    }
    *ptr = NULL;
    return (0);
  }

#ifdef DEPLOY_FENCE
  __atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

#undef DEPLOY_FENCE

  ut_ad(val == 0xF0);

  /* 11110000 nnnnnnnn nnnnnnnn nnnnnnnn nnnnnnnn (32 bits) */
  if (end_ptr >= *ptr + 5) {
    val = mach_read_from_4(*ptr + 1);
    ut_ad(val > 0xFFFFFFF);
    *ptr += 5;
    return (static_cast<ib_uint32_t>(val));
  }

  *ptr = NULL;
  return (0);
}