/*****************************************************************************

Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.

This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation.  The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License, version 2.0, for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
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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"

#ifdef UNIV_NONINL
#include "mach0data.ic"
#endif

/*********************************************************//**
Reads a ulint in a compressed form if the log record fully contains it.
@return	pointer to end of the stored field, NULL if not complete */
UNIV_INTERN
byte*
mach_parse_compressed(
/*==================*/
	byte*	ptr,	/*!< in: pointer to buffer from where to read */
	byte*	end_ptr,/*!< in: pointer to end of the buffer */
	ulint*	val)	/*!< out: read value (< 2^32) */
{
	ulint	flag;

	ut_ad(ptr && end_ptr && val);

	if (ptr >= end_ptr) {

		return(NULL);
	}

	flag = mach_read_from_1(ptr);

	if (flag < 0x80UL) {
		*val = flag;
		return(ptr + 1);
	}

	/* 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 (flag < 0xC0UL) {
		if (end_ptr < ptr + 2) {
			return(NULL);
		}

		*val = mach_read_from_2(ptr) & 0x7FFFUL;

		return(ptr + 2);
	}

#ifdef DEPLOY_FENCE
	__atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

	if (flag < 0xE0UL) {
		if (end_ptr < ptr + 3) {
			return(NULL);
		}

		*val = mach_read_from_3(ptr) & 0x3FFFFFUL;

		return(ptr + 3);
	}

#ifdef DEPLOY_FENCE
	__atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

	if (flag < 0xF0UL) {
		if (end_ptr < ptr + 4) {
			return(NULL);
		}

		*val = mach_read_from_4(ptr) & 0x1FFFFFFFUL;

		return(ptr + 4);
	}

#ifdef DEPLOY_FENCE
	__atomic_thread_fence(__ATOMIC_ACQUIRE);
#endif

#undef DEPLOY_FENCE

	ut_ad(flag == 0xF0UL);

	if (end_ptr < ptr + 5) {
		return(NULL);
	}

	*val = mach_read_from_4(ptr + 1);
	return(ptr + 5);
}
