1 /* $OpenBSD: sfsqrt.c,v 1.8 2023/03/08 04:43:07 guenther Exp $ */
2 /*
3 (c) Copyright 1986 HEWLETT-PACKARD COMPANY
4 To anyone who acknowledges that this file is provided "AS IS"
5 without any express or implied warranty:
6 permission to use, copy, modify, and distribute this file
7 for any purpose is hereby granted without fee, provided that
8 the above copyright notice and this notice appears in all
9 copies, and that the name of Hewlett-Packard Company not be
10 used in advertising or publicity pertaining to distribution
11 of the software without specific, written prior permission.
12 Hewlett-Packard Company makes no representations about the
13 suitability of this software for any purpose.
14 */
15 /* @(#)sfsqrt.c: Revision: 1.9.88.1 Date: 93/12/07 15:07:13 */
16
17 #include "float.h"
18 #include "sgl_float.h"
19
20 /*
21 * Single Floating-point Square Root
22 */
23
24 int
sgl_fsqrt(srcptr,null,dstptr,status)25 sgl_fsqrt(srcptr, null, dstptr, status)
26 sgl_floating_point *srcptr, *null, *dstptr;
27 unsigned int *status;
28 {
29 register unsigned int src, result;
30 register int src_exponent, newbit, sum;
31 register int guardbit = FALSE, even_exponent;
32
33 src = *srcptr;
34 /*
35 * check source operand for NaN or infinity
36 */
37 if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
38 /*
39 * is signaling NaN?
40 */
41 if (Sgl_isone_signaling(src)) {
42 /* trap if INVALIDTRAP enabled */
43 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
44 /* make NaN quiet */
45 Set_invalidflag();
46 Sgl_set_quiet(src);
47 }
48 /*
49 * Return quiet NaN or positive infinity.
50 * Fall thru to negative test if negative infinity.
51 */
52 if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
53 *dstptr = src;
54 return(NOEXCEPTION);
55 }
56 }
57
58 /*
59 * check for zero source operand
60 */
61 if (Sgl_iszero_exponentmantissa(src)) {
62 *dstptr = src;
63 return(NOEXCEPTION);
64 }
65
66 /*
67 * check for negative source operand
68 */
69 if (Sgl_isone_sign(src)) {
70 /* trap if INVALIDTRAP enabled */
71 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
72 /* make NaN quiet */
73 Set_invalidflag();
74 Sgl_makequietnan(src);
75 *dstptr = src;
76 return(NOEXCEPTION);
77 }
78
79 /*
80 * Generate result
81 */
82 if (src_exponent > 0) {
83 even_exponent = Sgl_hidden(src);
84 Sgl_clear_signexponent_set_hidden(src);
85 }
86 else {
87 /* normalize operand */
88 Sgl_clear_signexponent(src);
89 src_exponent++;
90 Sgl_normalize(src,src_exponent);
91 even_exponent = src_exponent & 1;
92 }
93 if (even_exponent) {
94 /* exponent is even */
95 /* Add comment here. Explain why odd exponent needs correction */
96 Sgl_leftshiftby1(src);
97 }
98 /*
99 * Add comment here. Explain following algorithm.
100 *
101 * Trust me, it works.
102 *
103 */
104 Sgl_setzero(result);
105 newbit = 1 << SGL_P;
106 while (newbit && Sgl_isnotzero(src)) {
107 Sgl_addition(result,newbit,sum);
108 if(sum <= Sgl_all(src)) {
109 /* update result */
110 Sgl_addition(result,(newbit<<1),result);
111 Sgl_subtract(src,sum,src);
112 }
113 Sgl_rightshiftby1(newbit);
114 Sgl_leftshiftby1(src);
115 }
116 /* correct exponent for pre-shift */
117 if (even_exponent) {
118 Sgl_rightshiftby1(result);
119 }
120
121 /* check for inexact */
122 if (Sgl_isnotzero(src)) {
123 if (!even_exponent & Sgl_islessthan(result,src))
124 Sgl_increment(result);
125 guardbit = Sgl_lowmantissa(result);
126 Sgl_rightshiftby1(result);
127
128 /* now round result */
129 switch (Rounding_mode()) {
130 case ROUNDPLUS:
131 Sgl_increment(result);
132 break;
133 case ROUNDNEAREST:
134 /* stickybit is always true, so guardbit
135 * is enough to determine rounding */
136 if (guardbit) {
137 Sgl_increment(result);
138 }
139 break;
140 }
141 /* increment result exponent by 1 if mantissa overflowed */
142 if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
143
144 if (Is_inexacttrap_enabled()) {
145 Sgl_set_exponent(result,
146 ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
147 *dstptr = result;
148 return(INEXACTEXCEPTION);
149 }
150 else Set_inexactflag();
151 }
152 else {
153 Sgl_rightshiftby1(result);
154 }
155 Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
156 *dstptr = result;
157 return(NOEXCEPTION);
158 }
159