cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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dfsqrt.c (4841B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/*
      3 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
      4 *
      5 * Floating-point emulation code
      6 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
      7 */
      8/*
      9 * BEGIN_DESC
     10 *
     11 *  File:
     12 *	@(#)	pa/spmath/dfsqrt.c		$Revision: 1.1 $
     13 *
     14 *  Purpose:
     15 *	Double Floating-point Square Root
     16 *
     17 *  External Interfaces:
     18 *	dbl_fsqrt(srcptr,nullptr,dstptr,status)
     19 *
     20 *  Internal Interfaces:
     21 *
     22 *  Theory:
     23 *	<<please update with a overview of the operation of this file>>
     24 *
     25 * END_DESC
     26*/
     27
     28
     29#include "float.h"
     30#include "dbl_float.h"
     31
     32/*
     33 *  Double Floating-point Square Root
     34 */
     35
     36/*ARGSUSED*/
     37unsigned int
     38dbl_fsqrt(
     39	    dbl_floating_point *srcptr,
     40	    unsigned int *nullptr,
     41	    dbl_floating_point *dstptr,
     42	    unsigned int *status)
     43{
     44	register unsigned int srcp1, srcp2, resultp1, resultp2;
     45	register unsigned int newbitp1, newbitp2, sump1, sump2;
     46	register int src_exponent;
     47	register boolean guardbit = FALSE, even_exponent;
     48
     49	Dbl_copyfromptr(srcptr,srcp1,srcp2);
     50        /*
     51         * check source operand for NaN or infinity
     52         */
     53        if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) {
     54                /*
     55                 * is signaling NaN?
     56                 */
     57                if (Dbl_isone_signaling(srcp1)) {
     58                        /* trap if INVALIDTRAP enabled */
     59                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
     60                        /* make NaN quiet */
     61                        Set_invalidflag();
     62                        Dbl_set_quiet(srcp1);
     63                }
     64                /*
     65                 * Return quiet NaN or positive infinity.
     66		 *  Fall through to negative test if negative infinity.
     67                 */
     68		if (Dbl_iszero_sign(srcp1) || 
     69		    Dbl_isnotzero_mantissa(srcp1,srcp2)) {
     70                	Dbl_copytoptr(srcp1,srcp2,dstptr);
     71                	return(NOEXCEPTION);
     72		}
     73        }
     74
     75        /*
     76         * check for zero source operand
     77         */
     78	if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) {
     79		Dbl_copytoptr(srcp1,srcp2,dstptr);
     80		return(NOEXCEPTION);
     81	}
     82
     83        /*
     84         * check for negative source operand 
     85         */
     86	if (Dbl_isone_sign(srcp1)) {
     87		/* trap if INVALIDTRAP enabled */
     88		if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
     89		/* make NaN quiet */
     90		Set_invalidflag();
     91		Dbl_makequietnan(srcp1,srcp2);
     92		Dbl_copytoptr(srcp1,srcp2,dstptr);
     93		return(NOEXCEPTION);
     94	}
     95
     96	/*
     97	 * Generate result
     98	 */
     99	if (src_exponent > 0) {
    100		even_exponent = Dbl_hidden(srcp1);
    101		Dbl_clear_signexponent_set_hidden(srcp1);
    102	}
    103	else {
    104		/* normalize operand */
    105		Dbl_clear_signexponent(srcp1);
    106		src_exponent++;
    107		Dbl_normalize(srcp1,srcp2,src_exponent);
    108		even_exponent = src_exponent & 1;
    109	}
    110	if (even_exponent) {
    111		/* exponent is even */
    112		/* Add comment here.  Explain why odd exponent needs correction */
    113		Dbl_leftshiftby1(srcp1,srcp2);
    114	}
    115	/*
    116	 * Add comment here.  Explain following algorithm.
    117	 * 
    118	 * Trust me, it works.
    119	 *
    120	 */
    121	Dbl_setzero(resultp1,resultp2);
    122	Dbl_allp1(newbitp1) = 1 << (DBL_P - 32);
    123	Dbl_setzero_mantissap2(newbitp2);
    124	while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) {
    125		Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2);
    126		if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) {
    127			Dbl_leftshiftby1(newbitp1,newbitp2);
    128			/* update result */
    129			Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,
    130			 resultp1,resultp2);  
    131			Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2);
    132			Dbl_rightshiftby2(newbitp1,newbitp2);
    133		}
    134		else {
    135			Dbl_rightshiftby1(newbitp1,newbitp2);
    136		}
    137		Dbl_leftshiftby1(srcp1,srcp2);
    138	}
    139	/* correct exponent for pre-shift */
    140	if (even_exponent) {
    141		Dbl_rightshiftby1(resultp1,resultp2);
    142	}
    143
    144	/* check for inexact */
    145	if (Dbl_isnotzero(srcp1,srcp2)) {
    146		if (!even_exponent && Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) {
    147			Dbl_increment(resultp1,resultp2);
    148		}
    149		guardbit = Dbl_lowmantissap2(resultp2);
    150		Dbl_rightshiftby1(resultp1,resultp2);
    151
    152		/*  now round result  */
    153		switch (Rounding_mode()) {
    154		case ROUNDPLUS:
    155		     Dbl_increment(resultp1,resultp2);
    156		     break;
    157		case ROUNDNEAREST:
    158		     /* stickybit is always true, so guardbit 
    159		      * is enough to determine rounding */
    160		     if (guardbit) {
    161			    Dbl_increment(resultp1,resultp2);
    162		     }
    163		     break;
    164		}
    165		/* increment result exponent by 1 if mantissa overflowed */
    166		if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2;
    167
    168		if (Is_inexacttrap_enabled()) {
    169			Dbl_set_exponent(resultp1,
    170			 ((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
    171			Dbl_copytoptr(resultp1,resultp2,dstptr);
    172			return(INEXACTEXCEPTION);
    173		}
    174		else Set_inexactflag();
    175	}
    176	else {
    177		Dbl_rightshiftby1(resultp1,resultp2);
    178	}
    179	Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
    180	Dbl_copytoptr(resultp1,resultp2,dstptr);
    181	return(NOEXCEPTION);
    182}