ieeefloat.c

mp3编码库

/* Copyright (C) 1988-1991 Apple Computer, Inc.
 * All Rights Reserved.
 *
 * Warranty Information
 * Even though Apple has reviewed this software, Apple makes no warranty
 * or representation, either express or implied, with respect to this
 * software, its quality, accuracy, merchantability, or fitness for a 
 * particular purpose.  As a result, this software is provided "as is,"
 * and you, its user, are assuming the entire risk as to its quality
 * and accuracy.
 *
 * This code may be used and freely distributed as long as it includes
 * this copyright notice and the warranty information.
 *
 * Machine-independent I/O routines for IEEE floating-point numbers.
 *
 * NaN's and infinities are converted to HUGE_VAL or HUGE, which
 * happens to be infinity on IEEE machines.  Unfortunately, it is
 * impossible to preserve NaN's in a machine-independent way.
 * Infinities are, however, preserved on IEEE machines.
 *
 * These routines have been tested on the following machines:
 *	Apple Macintosh, MPW 3.1 C compiler
 *	Apple Macintosh, THINK C compiler
 *	Silicon Graphics IRIS, MIPS compiler
 *	Cray X/MP and Y/MP
 *	Digital Equipment VAX
 *	Sequent Balance (Multiprocesor 386)
 *	NeXT
 *
 *
 * Implemented by Malcolm Slaney and Ken Turkowski.
 *
 * Malcolm Slaney contributions during 1988-1990 include big- and little-
 * endian file I/O, conversion to and from Motorola's extended 80-bit
 * floating-point format, and conversions to and from IEEE single-
 * precision floating-point format.
 *
 * In 1991, Ken Turkowski implemented the conversions to and from
 * IEEE double-precision format, added more precision to the extended
 * conversions, and accommodated conversions involving +/- infinity,
 * NaN's, and denormalized numbers.
 *
 * $Id: ieeefloat.c,v 1.1 1993/06/11 17:45:46 malcolm Exp $
 *
 * $Log: ieeefloat.c,v $
 * Revision 1.1  1993/06/11  17:45:46  malcolm
 * Initial revision
 *
 */

#include	<stdio.h>
#include	<math.h>
#include	"./libmp3enc/libmp3enc.h"
#include	"ieeefloat.h"


/****************************************************************
 * The following two routines make up for deficiencies in many
 * compilers to convert properly between unsigned integers and
 * floating-point.  Some compilers which have this bug are the
 * THINK_C compiler for the Macintosh and the C compiler for the
 * Silicon Graphics MIPS-based Iris.
 ****************************************************************/

#ifdef applec	/* The Apple C compiler works */
# define FloatToUnsigned(f)	((u32)(f))
# define UnsignedToFloat(u)	((defdouble)(u))
#else /* applec */
# define FloatToUnsigned(f)	((u32)(((i32)((f) - 2147483648.0)) + 2147483647L + 1))
# define UnsignedToFloat(u)	(((defdouble)((i32)((u) - 2147483647L - 1))) + 2147483648.0)
#endif /* applec */


/****************************************************************
 * Single precision IEEE floating-point conversion routines
 ****************************************************************/

#define SEXP_MAX		255
#define SEXP_OFFSET		127
#define SEXP_SIZE		8
#define SEXP_POSITION	(32-SEXP_SIZE-1)


/****************************************************************
 * Extended precision IEEE floating-point conversion routines
 ****************************************************************/

defdouble
ConvertFromIeeeExtended(bytes)
i8* bytes;
{
	defdouble	f;
	i32	expon;
	u32 hiMant, loMant;

#ifdef	TEST	
printf("ConvertFromIEEEExtended(%lx,%lx,%lx,%lx,%lx,%lx,%lx,%lx,%lx,%lx\r",
	(i32)bytes[0], (i32)bytes[1], (i32)bytes[2], (i32)bytes[3], 
	(i32)bytes[4], (i32)bytes[5], (i32)bytes[6], 
	(i32)bytes[7], (i32)bytes[8], (i32)bytes[9]);
#endif
	
	expon = ((bytes[0] & 0x7F) << 8) | (bytes[1] & 0xFF);
	hiMant	=	((u32)(bytes[2] & 0xFF) << 24)
			|	((u32)(bytes[3] & 0xFF) << 16)
			|	((u32)(bytes[4] & 0xFF) << 8)
			|	((u32)(bytes[5] & 0xFF));
	loMant	=	((u32)(bytes[6] & 0xFF) << 24)
			|	((u32)(bytes[7] & 0xFF) << 16)
			|	((u32)(bytes[8] & 0xFF) << 8)
			|	((u32)(bytes[9] & 0xFF));

	if (expon == 0 && hiMant == 0 && loMant == 0) {
		f = 0;
	}
	else {
		if (expon == 0x7FFF) {	/* Infinity or NaN */
			f = HUGE_VAL;
		}
#ifdef WIN32
		else {
			printf("hi, i'm here\n");
			expon -= 16383;
			f  = ldexp(UnsignedToFloat(hiMant), expon-=31);
			f += ldexp(UnsignedToFloat(loMant), expon-=32);
		}
#endif
	}

	if (bytes[0] & 0x80)
		return -f;
	else
		return f;
}