ldexp.S revision 1.8.46.1
1 /* $NetBSD: ldexp.S,v 1.8.46.1 2009/08/16 03:36:02 matt 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 RCSID("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93") 39 RCSID("$NetBSD: ldexp.S,v 1.8.46.1 2009/08/16 03:36:02 matt Exp $") 40 #endif /* LIBC_SCCS and not lint */ 41 42 #define DEXP_INF 0x7ff 43 #define DEXP_BIAS 1023 44 #define DEXP_MIN -1022 45 #define DEXP_MAX 1023 46 #define DFRAC_BITS 52 47 #define DIMPL_ONE 0x00100000 48 #define DLEAD_ZEROS 31 - 20 49 #define STICKYBIT 1 50 #define GUARDBIT 0x80000000 51 #define DSIGNAL_NAN 0x00040000 52 #define DQUIET_NAN0 0x0007ffff 53 #define DQUIET_NAN1 0xffffffff 54 55 /* 56 * double ldexp(x, N) 57 * double x; int N; 58 * 59 * Return x * (2**N), for integer values N. 60 */ 61 LEAF(ldexp) 62 mfc1 v1, $f13 # get MSW of x 63 mfc1 t3, $f12 # get LSW of x 64 sll t1, v1, 1 # get x exponent 65 srl t1, t1, 32 - 11 66 beq t1, DEXP_INF, 9f # is it a NAN or infinity? 67 beq t1, zero, 1f # zero or denormalized number? 68 addu t1, t1, a2 # scale exponent 69 sll v0, a2, 20 # position N for addition 70 bge t1, DEXP_INF, 8f # overflow? 71 addu v0, v0, v1 # multiply by (2**N) 72 ble t1, zero, 4f # underflow? 73 mtc1 v0, $f1 # save MSW of result 74 mtc1 t3, $f0 # save LSW of result 75 j ra 76 1: 77 sll t2, v1, 32 - 20 # get x fraction 78 srl t2, t2, 32 - 20 79 srl t0, v1, 31 # get x sign 80 bne t2, zero, 1f 81 beq t3, zero, 9f # result is zero 82 1: 83 /* 84 * Find out how many leading zero bits are in t2,t3 and put in t9. 85 */ 86 move v0, t2 87 move t9, zero 88 bne t2, zero, 1f 89 move v0, t3 90 addu t9, 32 91 1: 92 srl ta0, v0, 16 93 bne ta0, zero, 1f 94 addu t9, 16 95 sll v0, 16 96 1: 97 srl ta0, v0, 24 98 bne ta0, zero, 1f 99 addu t9, 8 100 sll v0, 8 101 1: 102 srl ta0, v0, 28 103 bne ta0, zero, 1f 104 addu t9, 4 105 sll v0, 4 106 1: 107 srl ta0, v0, 30 108 bne ta0, zero, 1f 109 addu t9, 2 110 sll v0, 2 111 1: 112 srl ta0, v0, 31 113 bne ta0, zero, 1f 114 addu t9, 1 115 /* 116 * Now shift t2,t3 the correct number of bits. 117 */ 118 1: 119 subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros 120 li t1, DEXP_MIN + DEXP_BIAS 121 subu t1, t1, t9 # adjust exponent 122 addu t1, t1, a2 # scale exponent 123 li v0, 32 124 blt t9, v0, 1f 125 subu t9, t9, v0 # shift fraction left >= 32 bits 126 sll t2, t3, t9 127 move t3, zero 128 b 2f 129 1: 130 subu v0, v0, t9 # shift fraction left < 32 bits 131 sll t2, t2, t9 132 srl ta0, t3, v0 133 or t2, t2, ta0 134 sll t3, t3, t9 135 2: 136 bge t1, DEXP_INF, 8f # overflow? 137 ble t1, zero, 4f # underflow? 138 sll t2, t2, 32 - 20 # clear implied one bit 139 srl t2, t2, 32 - 20 140 3: 141 sll t1, t1, 31 - 11 # reposition exponent 142 sll t0, t0, 31 # reposition sign 143 or t0, t0, t1 # put result back together 144 or t0, t0, t2 145 mtc1 t0, $f1 # save MSW of result 146 mtc1 t3, $f0 # save LSW of result 147 j ra 148 4: 149 li v0, 0x80000000 150 ble t1, -52, 7f # is result too small for denorm? 151 sll t2, v1, 31 - 20 # clear exponent, extract fraction 152 or t2, t2, v0 # set implied one bit 153 blt t1, -30, 2f # will all bits in t3 be shifted out? 154 srl t2, t2, 31 - 20 # shift fraction back to normal position 155 subu t1, t1, 1 156 sll ta0, t2, t1 # shift right t2,t3 based on exponent 157 srl t8, t3, t1 # save bits shifted out 158 negu t1 159 srl t3, t3, t1 160 or t3, t3, ta0 161 srl t2, t2, t1 162 bge t8, zero, 1f # does result need to be rounded? 163 addu t3, t3, 1 # round result 164 sltu ta0, t3, 1 165 sll t8, t8, 1 166 addu t2, t2, ta0 167 bne t8, zero, 1f # round result to nearest 168 and t3, t3, ~1 169 1: 170 mtc1 t3, $f0 # save denormalized result (LSW) 171 mtc1 t2, $f1 # save denormalized result (MSW) 172 bge v1, zero, 1f # should result be negative? 173 neg.d $f0, $f0 # negate result 174 1: 175 j ra 176 2: 177 mtc1 zero, $f1 # exponent and upper fraction 178 addu t1, t1, 20 # compute amount to shift right by 179 sll t8, t2, t1 # save bits shifted out 180 negu t1 181 srl t3, t2, t1 182 bge t8, zero, 1f # does result need to be rounded? 183 addu t3, t3, 1 # round result 184 sltu ta0, t3, 1 185 sll t8, t8, 1 186 mtc1 ta0, $f1 # exponent and upper fraction 187 bne t8, zero, 1f # round result to nearest 188 and t3, t3, ~1 189 1: 190 mtc1 t3, $f0 191 bge v1, zero, 1f # is result negative? 192 neg.d $f0, $f0 # negate result 193 1: 194 j ra 195 7: 196 mtc1 zero, $f0 # result is zero 197 mtc1 zero, $f1 198 beq t0, zero, 1f # is result positive? 199 neg.d $f0, $f0 # negate result 200 1: 201 j ra 202 8: 203 li t1, 0x7ff00000 # result is infinity (MSW) 204 mtc1 t1, $f1 205 mtc1 zero, $f0 # result is infinity (LSW) 206 bge v1, zero, 1f # should result be negative infinity? 207 neg.d $f0, $f0 # result is negative infinity 208 1: 209 add.d $f0, $f0 # cause overflow faults if enabled 210 j ra 211 9: 212 mov.d $f0, $f12 # yes, result is just x 213 j ra 214 END(ldexp) 215
Indexes created Fri Oct 03 02:09:57 GMT 2025