dfsqrt.c

  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}