jpc_math.c

用C语言实现的JPEG编码

/*
 * Copyright (c) 1999-2000 Image Power, Inc. and the University of
 *   British Columbia.
 * Copyright (c) 2001-2002 Michael David Adams.
 * All rights reserved.
 */

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/*
 * Math Library
 *
 * $Id$
 */

/******************************************************************************\
* Includes
\******************************************************************************/

#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <stdarg.h>

#include "jpc_math.h"

/******************************************************************************\
* Miscellaneous Functions
\******************************************************************************/

/* Calculate the integer quantity floor(log2(x)), where x is a positive
  integer. */
int jpc_floorlog2(int x)
{
	int y;

	/* The argument must be positive. */
	assert(x > 0);

	y = 0;
	while (x > 1) {
		x >>= 1;
		++y;
	}
	return y;
}

/* Calculate the bit position of the first leading one in a nonnegative
  integer. */
/* This function is the basically the same as ceillog2(x), except that the
  allowable range for x is slightly different. */
int jpc_firstone(int x)
{
	int n;

	/* The argument must be nonnegative. */
	assert(x >= 0);

	n = -1;
	while (x > 0) {
		x >>= 1;
		++n;
	}
	return n;
}