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1.1 nbrk 1: /* $OpenBSD: sfsqrt.c,v 1.7 2003/04/10 17:27:59 mickey 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: /*ARGSUSED*/
25: int
26: sgl_fsqrt(srcptr, null, dstptr, status)
27: sgl_floating_point *srcptr, *null, *dstptr;
28: unsigned int *status;
29: {
30: register unsigned int src, result;
31: register int src_exponent, newbit, sum;
32: register int guardbit = FALSE, even_exponent;
33:
34: src = *srcptr;
35: /*
36: * check source operand for NaN or infinity
37: */
38: if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
39: /*
40: * is signaling NaN?
41: */
42: if (Sgl_isone_signaling(src)) {
43: /* trap if INVALIDTRAP enabled */
44: if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
45: /* make NaN quiet */
46: Set_invalidflag();
47: Sgl_set_quiet(src);
48: }
49: /*
50: * Return quiet NaN or positive infinity.
51: * Fall thru to negative test if negative infinity.
52: */
53: if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
54: *dstptr = src;
55: return(NOEXCEPTION);
56: }
57: }
58:
59: /*
60: * check for zero source operand
61: */
62: if (Sgl_iszero_exponentmantissa(src)) {
63: *dstptr = src;
64: return(NOEXCEPTION);
65: }
66:
67: /*
68: * check for negative source operand
69: */
70: if (Sgl_isone_sign(src)) {
71: /* trap if INVALIDTRAP enabled */
72: if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
73: /* make NaN quiet */
74: Set_invalidflag();
75: Sgl_makequietnan(src);
76: *dstptr = src;
77: return(NOEXCEPTION);
78: }
79:
80: /*
81: * Generate result
82: */
83: if (src_exponent > 0) {
84: even_exponent = Sgl_hidden(src);
85: Sgl_clear_signexponent_set_hidden(src);
86: }
87: else {
88: /* normalize operand */
89: Sgl_clear_signexponent(src);
90: src_exponent++;
91: Sgl_normalize(src,src_exponent);
92: even_exponent = src_exponent & 1;
93: }
94: if (even_exponent) {
95: /* exponent is even */
96: /* Add comment here. Explain why odd exponent needs correction */
97: Sgl_leftshiftby1(src);
98: }
99: /*
100: * Add comment here. Explain following algorithm.
101: *
102: * Trust me, it works.
103: *
104: */
105: Sgl_setzero(result);
106: newbit = 1 << SGL_P;
107: while (newbit && Sgl_isnotzero(src)) {
108: Sgl_addition(result,newbit,sum);
109: if(sum <= Sgl_all(src)) {
110: /* update result */
111: Sgl_addition(result,(newbit<<1),result);
112: Sgl_subtract(src,sum,src);
113: }
114: Sgl_rightshiftby1(newbit);
115: Sgl_leftshiftby1(src);
116: }
117: /* correct exponent for pre-shift */
118: if (even_exponent) {
119: Sgl_rightshiftby1(result);
120: }
121:
122: /* check for inexact */
123: if (Sgl_isnotzero(src)) {
124: if (!even_exponent & Sgl_islessthan(result,src))
125: Sgl_increment(result);
126: guardbit = Sgl_lowmantissa(result);
127: Sgl_rightshiftby1(result);
128:
129: /* now round result */
130: switch (Rounding_mode()) {
131: case ROUNDPLUS:
132: Sgl_increment(result);
133: break;
134: case ROUNDNEAREST:
135: /* stickybit is always true, so guardbit
136: * is enough to determine rounding */
137: if (guardbit) {
138: Sgl_increment(result);
139: }
140: break;
141: }
142: /* increment result exponent by 1 if mantissa overflowed */
143: if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
144:
145: if (Is_inexacttrap_enabled()) {
146: Sgl_set_exponent(result,
147: ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
148: *dstptr = result;
149: return(INEXACTEXCEPTION);
150: }
151: else Set_inexactflag();
152: }
153: else {
154: Sgl_rightshiftby1(result);
155: }
156: Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
157: *dstptr = result;
158: return(NOEXCEPTION);
159: }