ldexp.S revision 1.10
1 /* $NetBSD: ldexp.S,v 1.10 2014/09/17 11:01:05 joerg Exp $ */ 2 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 */ 34 35 #include <mips/asm.h> 36 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 1.10 2014/09/17 11:01:05 joerg Exp $") 42 #endif 43 #endif /* LIBC_SCCS and not lint */ 44 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 57 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, $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) 218
Indexes created Fri Oct 03 15:10:06 GMT 2025