| blob | 8dab2a63bc589ea8de9d04834d763fcf3a264540 |
1 /* $NetBSD: ldexp.S,v 1.8.46.2 2009/08/18 06:52:09 matt Exp $ */
3 /*-
4 * Copyright (c) 1991, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Ralph Campbell.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
35 #include <mips/asm.h>
37 #if defined(LIBC_SCCS) && !defined(lint)
38 #if 0
39 RCSID("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93")
40 #else
41 RCSID("$NetBSD: ldexp.S,v 1.8.46.2 2009/08/18 06:52:09 matt Exp $")
42 #endif
43 #endif /* LIBC_SCCS and not lint */
45 #define DEXP_INF 0x7ff
46 #define DEXP_BIAS 1023
47 #define DEXP_MIN -1022
48 #define DEXP_MAX 1023
49 #define DFRAC_BITS 52
50 #define DIMPL_ONE 0x00100000
51 #define DLEAD_ZEROS 31 - 20
52 #define STICKYBIT 1
53 #define GUARDBIT 0x80000000
54 #define DSIGNAL_NAN 0x00040000
55 #define DQUIET_NAN0 0x0007ffff
56 #define DQUIET_NAN1 0xffffffff
58 /*
59 * double ldexp(x, N)
60 * double x; int N;
61 *
62 * Return x * (2**N), for integer values N.
63 */
64 LEAF(ldexp)
65 mfc1 v1, $f13 # get MSW of x
66 mfc1 t3, $f12 # get LSW of x
67 sll t1, v1, 1 # get x exponent
68 srl t1, t1, 32 - 11
69 beq t1, DEXP_INF, 9f # is it a NAN or infinity?
70 beq t1, zero, 1f # zero or denormalized number?
71 addu t1, t1, a2 # scale exponent
72 sll v0, a2, 20 # position N for addition
73 bge t1, DEXP_INF, 8f # overflow?
74 addu v0, v0, v1 # multiply by (2**N)
75 ble t1, zero, 4f # underflow?
76 mtc1 v0, $f1 # save MSW of result
77 mtc1 t3, $f0 # save LSW of result
78 j ra
79 1:
80 sll t2, v1, 32 - 20 # get x fraction
81 srl t2, t2, 32 - 20
82 srl t0, v1, 31 # get x sign
83 bne t2, zero, 1f
84 beq t3, zero, 9f # result is zero
85 1:
86 /*
87 * Find out how many leading zero bits are in t2,t3 and put in t9.
88 */
89 move v0, t2
90 move t9, zero
91 bne t2, zero, 1f
92 move v0, t3
93 addu t9, 32
94 1:
95 srl ta0, v0, 16
96 bne ta0, zero, 1f
97 addu t9, 16
98 sll v0, 16
99 1:
100 srl ta0, v0, 24
101 bne ta0, zero, 1f
102 addu t9, 8
103 sll v0, 8
104 1:
105 srl ta0, v0, 28
106 bne ta0, zero, 1f
107 addu t9, 4
108 sll v0, 4
109 1:
110 srl ta0, v0, 30
111 bne ta0, zero, 1f
112 addu t9, 2
113 sll v0, 2
114 1:
115 srl ta0, v0, 31
116 bne ta0, zero, 1f
117 addu t9, 1
118 /*
119 * Now shift t2,t3 the correct number of bits.
120 */
121 1:
122 subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros
123 li t1, DEXP_MIN + DEXP_BIAS
124 subu t1, t1, t9 # adjust exponent
125 addu t1, t1, a2 # scale exponent
126 li v0, 32
127 blt t9, v0, 1f
128 subu t9, t9, v0 # shift fraction left >= 32 bits
129 sll t2, t3, t9
130 move t3, zero
131 b 2f
132 1:
133 subu v0, v0, t9 # shift fraction left < 32 bits
134 sll t2, t2, t9
135 srl ta0, t3, v0
136 or t2, t2, ta0
137 sll t3, t3, t9
138 2:
139 bge t1, DEXP_INF, 8f # overflow?
140 ble t1, zero, 4f # underflow?
141 sll t2, t2, 32 - 20 # clear implied one bit
142 srl t2, t2, 32 - 20
143 3:
144 sll t1, t1, 31 - 11 # reposition exponent
145 sll t0, t0, 31 # reposition sign
146 or t0, t0, t1 # put result back together
147 or t0, t0, t2
148 mtc1 t0, $f1 # save MSW of result
149 mtc1 t3, $f0 # save LSW of result
150 j ra
151 4:
152 li v0, 0x80000000
153 ble t1, -52, 7f # is result too small for denorm?
154 sll t2, v1, 31 - 20 # clear exponent, extract fraction
155 or t2, t2, v0 # set implied one bit
156 blt t1, -30, 2f # will all bits in t3 be shifted out?
157 srl t2, t2, 31 - 20 # shift fraction back to normal position
158 subu t1, t1, 1
159 sll ta0, t2, t1 # shift right t2,t3 based on exponent
160 srl t8, t3, t1 # save bits shifted out
161 negu t1
162 srl t3, t3, t1
163 or t3, t3, ta0
164 srl t2, t2, t1
165 bge t8, zero, 1f # does result need to be rounded?
166 addu t3, t3, 1 # round result
167 sltu ta0, t3, 1
168 sll t8, t8, 1
169 addu t2, t2, ta0
170 bne t8, zero, 1f # round result to nearest
171 and t3, t3, ~1
172 1:
173 mtc1 t3, $f0 # save denormalized result (LSW)
174 mtc1 t2, $f1 # save denormalized result (MSW)
175 bge v1, zero, 1f # should result be negative?
176 neg.d $f0, $f0 # negate result
177 1:
178 j ra
179 2:
180 mtc1 zero, $f1 # exponent and upper fraction
181 addu t1, t1, 20 # compute amount to shift right by
182 sll t8, t2, t1 # save bits shifted out
183 negu t1
184 srl t3, t2, t1
185 bge t8, zero, 1f # does result need to be rounded?
186 addu t3, t3, 1 # round result
187 sltu ta0, t3, 1
188 sll t8, t8, 1
189 mtc1 ta0, $f1 # exponent and upper fraction
190 bne t8, zero, 1f # round result to nearest
191 and t3, t3, ~1
192 1:
193 mtc1 t3, $f0
194 bge v1, zero, 1f # is result negative?
195 neg.d $f0, $f0 # negate result
196 1:
197 j ra
198 7:
199 mtc1 zero, $f0 # result is zero
200 mtc1 zero, $f1
201 beq t0, zero, 1f # is result positive?
202 neg.d $f0, $f0 # negate result
203 1:
204 j ra
205 8:
206 li t1, 0x7ff00000 # result is infinity (MSW)
207 mtc1 t1, $f1
208 mtc1 zero, $f0 # result is infinity (LSW)
209 bge v1, zero, 1f # should result be negative infinity?
210 neg.d $f0, $f0 # result is negative infinity
211 1:
212 add.d $f0, $f0 # cause overflow faults if enabled
213 j ra
214 9:
215 mov.d $f0, $f12 # yes, result is just x
216 j ra
217 END(ldexp)