hypot.c   [plain text]


/*
 * Copyright (c) 2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*******************************************************************************
*                                                                              *
*      File hypot.c,                                                           *
*      Function hypot(x,y),                                                    *
*      Implementation of sqrt(x^2+y^2) for the PowerPC.                        *
*                                                                              *
*      Copyright  1991 Apple Computer, Inc.  All rights reserved.             *
*                                                                              *
*      Written by Ali Sazegari, started on November 1991,                      *
*                                                                              *
*      based on math.h, library code for Macintoshes with a 68881/68882        *
*      by Jim Thomas.                                                          *
*                                                                              *
*      W A R N I N G:  This routine expects a 64 bit double model.             *
*                                                                              *
*      December 03 1992: first rs6000 port.                                    *
*      January  05 1993: added the environmental controls.                     *
*      July     14 1993: added #pragma fenv_access. changed feholdexcept       *
*                        to the internal routine _feprocentry.                 *
*      September22 1993: conforming to nceg-fpce specification for  values.  *
*      September19 1994: revamp of the algorithm for performance.	       *
*                                                                              *
*******************************************************************************/

#include      "math.h"
#include      "fenv.h"
#include      "fp_private.h"
#include      "fenv_private.h"
#include <System/ppc/cpu_capabilities.h>

inline static uint32_t __attribute__((always_inline))
_get_cpu_capabilities(void) 
{
        uint32_t caps;
        asm("lwz %0, %1(0)" : "=r" (caps) : "I" (_COMM_PAGE_CPU_CAPABILITIES));
        return caps;
}

/*******************************************************************************
*            Functions needed for the computation.                             *
*******************************************************************************/

/*     the following fp.h functions are used:                                 */
/*     fabs and sqrt;                                                	      */
/*     the following environmental functions are used:                        */
/*     feclearexcept, _feprocentry and feupdateenv.                           */


#pragma STDC FENV_ACCESS ON

static const hexdouble Huge = HEXDOUBLE(0x7FF00000, 0x00000000);
static const hexdouble NegHuge = HEXDOUBLE(0xFFF00000, 0x00000000);

double hypot ( double x, double y )
{
        register double temp;
	hexdouble OldEnvironment, CurrentEnvironment;
        
        register double FPR_env, FPR_z, FPR_one, FPR_inf, FPR_Minf, 
                        FPR_absx, FPR_absy, FPR_big, FPR_small;
        
        FPR_z = 0.0;					FPR_one = 1.0;
        FPR_inf = Huge.d;				FPR_Minf = NegHuge.d;
        FPR_absx = __FABS( x );				FPR_absy = __FABS( y );
      
/*******************************************************************************
*     If argument is SNaN then a QNaN has to be returned and the invalid       *
*     flag signaled.                                                           * 
*******************************************************************************/
	
	if (unlikely( ( x == FPR_inf ) || ( y == FPR_inf ) || ( x == FPR_Minf ) || ( y == FPR_Minf ) ))
            return FPR_inf;
                
        if (unlikely( ( x != x ) || ( y != y ) ))
        {
            x = __FABS ( x + y );
            return x;
        }
            
        if ( FPR_absx > FPR_absy )
        {
            FPR_big = FPR_absx;
            FPR_small = FPR_absy;
        }
        else
        {
            FPR_big = FPR_absy;
            FPR_small = FPR_absx;
        }
        
        // Now +0.0 <= FPR_small <= FPR_big < INFINITY
        
        if (unlikely( FPR_small == FPR_z ))
            return FPR_big;
            
        FEGETENVD( FPR_env );				// save environment, set default
        FESETENVD( FPR_z );

        temp = FPR_small / FPR_big;			
	OldEnvironment.d = FPR_env;
	
	temp = FPR_one + temp * temp;	   
	if (likely((_get_cpu_capabilities() & kHasFsqrt)))
	    temp = __fsqrt ( temp );
	else
	    temp = sqrt ( temp );	   
        
        FEGETENVD_GRP( CurrentEnvironment.d );
        CurrentEnvironment.i.lo &= ~FE_UNDERFLOW;	// Clear any inconsequential underflow
        FESETENVD_GRP( CurrentEnvironment.d );
        
        temp = FPR_big * temp;				// Might raise UNDERFLOW or OVERFLOW
            
        FEGETENVD_GRP( CurrentEnvironment.d );
        OldEnvironment.i.lo |= CurrentEnvironment.i.lo; // Pick up any UF or OF
        FESETENVD_GRP( OldEnvironment.d );        		// restore caller's environment

        return temp;
}