common/m_fixed.h

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// Emacs style mode select   -*- C++ -*- 
//-----------------------------------------------------------------------------
//
// $Id: m_fixed.h 1788 2010-08-24 04:42:57Z russellrice $
//
// Copyright (C) 1993-1996 by id Software, Inc.
// Copyright (C) 2006-2010 by The Odamex Team.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// 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 for more details.
//
// DESCRIPTION:
//      Fixed point arithemtics, implementation.
//
//-----------------------------------------------------------------------------


#ifndef __M_FIXED__
#define __M_FIXED__

#include <stdlib.h>
#include "doomtype.h"

//
// Fixed point, 32bit as 16.16.
//
#define FRACBITS                                16
#define FRACUNIT                                (1<<FRACBITS)

typedef int fixed_t;            // fixed 16.16
typedef unsigned int dsfixed_t; // fixedpt used by span drawer

extern "C" fixed_t FixedMul_ASM                         (fixed_t a, fixed_t b);
extern "C" fixed_t STACK_ARGS FixedDiv_ASM      (fixed_t a, fixed_t b);
fixed_t FixedMul_C                              (fixed_t a, fixed_t b);
fixed_t FixedDiv_C                              (fixed_t a, fixed_t b);

#ifdef ALPHA
inline fixed_t FixedMul (fixed_t a, fixed_t b)
{
    return (fixed_t)(((long)a * (long)b) >> 16);
}

inline fixed_t FixedDiv (fixed_t a, fixed_t b)
{
    if (abs(a) >> 14 >= abs(b))
            return (a^b)<0 ? MININT : MAXINT;
        return (fixed_t)((((long)a) << 16) / b);
}

#else

#ifdef USEASM

#if defined(_MSC_VER)

__inline fixed_t FixedMul (fixed_t a, fixed_t b)
{
        fixed_t result;
        __asm {
                mov             eax,[a]
                imul    [b]
                shrd    eax,edx,16
                mov             [result],eax
        }
        return result;
}

#if 1
// Inlining FixedDiv with VC++ generates too many bad optimizations.
#define FixedDiv(a,b)                   FixedDiv_ASM(a,b)
#else
__inline fixed_t FixedDiv (fixed_t a, fixed_t b)
{
        if (abs(a) >> 14 >= abs(b))
                return (a^b)<0 ? MININT : MAXINT;
        else
        {
                fixed_t result;

                __asm {
                        mov             eax,[a]
                        mov             edx,[a]
                        sar             edx,16
                        shl             eax,16
                        idiv    [b]
                        mov             [result],eax
                }
                return result;
        }
}
#endif

#else

#define FixedMul(a,b)                   FixedMul_ASM(a,b)
#define FixedDiv(a,b)                   FixedDiv_ASM(a,b)

#endif

#else // !USEASM
#define FixedMul(a,b)                   FixedMul_C(a,b)
#define FixedDiv(a,b)                   FixedDiv_C(a,b)
#endif

#endif // !ALPHA

#endif