1/* $NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc 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 <machine/asm.h> 36__FBSDID("$FreeBSD$"); 37 38#if defined(LIBC_SCCS) && !defined(lint) 39 ASMSTR("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93") 40 ASMSTR("$NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc Exp $") 41#endif /* LIBC_SCCS and not lint */ 42 43#ifdef __ABICALLS__ 44 .abicalls 45#endif 46 47#define DEXP_INF 0x7ff 48#define DEXP_BIAS 1023 49#define DEXP_MIN -1022 50#define DEXP_MAX 1023 51#define DFRAC_BITS 52 52#define DIMPL_ONE 0x00100000 53#define DLEAD_ZEROS 31 - 20 54#define STICKYBIT 1 55#define GUARDBIT 0x80000000 56#define DSIGNAL_NAN 0x00040000 57#define DQUIET_NAN0 0x0007ffff 58#define DQUIET_NAN1 0xffffffff 59 60/* 61 * double ldexp(x, N) 62 * double x; int N; 63 * 64 * Return x * (2**N), for integer values N. 65 */ 66LEAF(ldexp) 67 mfc1 v1, $f13 # get MSW of x 68 mfc1 t3, $f12 # get LSW of x 69 sll t1, v1, 1 # get x exponent 70 srl t1, t1, 32 - 11 71 beq t1, DEXP_INF, 9f # is it a NAN or infinity? 72 beq t1, zero, 1f # zero or denormalized number? 73 addu t1, t1, a2 # scale exponent 74 sll v0, a2, 20 # position N for addition 75 bge t1, DEXP_INF, 8f # overflow? 76 addu v0, v0, v1 # multiply by (2**N) 77 ble t1, zero, 4f # underflow? 78 mtc1 v0, $f1 # save MSW of result 79 mtc1 t3, $f0 # save LSW of result 80 j ra 811: 82 sll t2, v1, 32 - 20 # get x fraction 83 srl t2, t2, 32 - 20 84 srl t0, v1, 31 # get x sign 85 bne t2, zero, 1f 86 beq t3, zero, 9f # result is zero 871: 88/* 89 * Find out how many leading zero bits are in t2,t3 and put in t9. 90 */ 91 move v0, t2 92 move t9, zero 93 bne t2, zero, 1f 94 move v0, t3 95 addu t9, 32 961: 97 srl ta0, v0, 16 98 bne ta0, zero, 1f 99 addu t9, 16 100 sll v0, 16 1011: 102 srl ta0, v0, 24 103 bne ta0, zero, 1f 104 addu t9, 8 105 sll v0, 8 1061: 107 srl ta0, v0, 28 108 bne ta0, zero, 1f 109 addu t9, 4 110 sll v0, 4 1111: 112 srl ta0, v0, 30 113 bne ta0, zero, 1f 114 addu t9, 2 115 sll v0, 2 1161: 117 srl ta0, v0, 31 118 bne ta0, zero, 1f 119 addu t9, 1 120/* 121 * Now shift t2,t3 the correct number of bits. 122 */ 1231: 124 subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros 125 li t1, DEXP_MIN + DEXP_BIAS 126 subu t1, t1, t9 # adjust exponent 127 addu t1, t1, a2 # scale exponent 128 li v0, 32 129 blt t9, v0, 1f 130 subu t9, t9, v0 # shift fraction left >= 32 bits 131 sll t2, t3, t9 132 move t3, zero 133 b 2f 1341: 135 subu v0, v0, t9 # shift fraction left < 32 bits 136 sll t2, t2, t9 137 srl ta0, t3, v0 138 or t2, t2, ta0 139 sll t3, t3, t9 1402: 141 bge t1, DEXP_INF, 8f # overflow? 142 ble t1, zero, 4f # underflow? 143 sll t2, t2, 32 - 20 # clear implied one bit 144 srl t2, t2, 32 - 20 1453: 146 sll t1, t1, 31 - 11 # reposition exponent 147 sll t0, t0, 31 # reposition sign 148 or t0, t0, t1 # put result back together 149 or t0, t0, t2 150 mtc1 t0, $f1 # save MSW of result 151 mtc1 t3, $f0 # save LSW of result 152 j ra 1534: 154 li v0, 0x80000000 155 ble t1, -52, 7f # is result too small for denorm? 156 sll t2, v1, 31 - 20 # clear exponent, extract fraction 157 or t2, t2, v0 # set implied one bit 158 blt t1, -30, 2f # will all bits in t3 be shifted out? 159 srl t2, t2, 31 - 20 # shift fraction back to normal position 160 subu t1, t1, 1 161 sll ta0, t2, t1 # shift right t2,t3 based on exponent 162 srl t8, t3, t1 # save bits shifted out 163 negu t1 164 srl t3, t3, t1 165 or t3, t3, ta0 166 srl t2, t2, t1 167 bge t8, zero, 1f # does result need to be rounded? 168 addu t3, t3, 1 # round result 169 sltu ta0, t3, 1 170 sll t8, t8, 1 171 addu t2, t2, ta0 172 bne t8, zero, 1f # round result to nearest 173 and t3, t3, ~1 1741: 175 mtc1 t3, $f0 # save denormalized result (LSW) 176 mtc1 t2, $f1 # save denormalized result (MSW) 177 bge v1, zero, 1f # should result be negative? 178 neg.d $f0, $f0 # negate result 1791: 180 j ra 1812: 182 mtc1 zero, $f1 # exponent and upper fraction 183 addu t1, t1, 20 # compute amount to shift right by 184 sll t8, t2, t1 # save bits shifted out 185 negu t1 186 srl t3, t2, t1 187 bge t8, zero, 1f # does result need to be rounded? 188 addu t3, t3, 1 # round result 189 sltu ta0, t3, 1 190 sll t8, t8, 1 191 mtc1 ta0, $f1 # exponent and upper fraction 192 bne t8, zero, 1f # round result to nearest 193 and t3, t3, ~1 1941: 195 mtc1 t3, $f0 196 bge v1, zero, 1f # is result negative? 197 neg.d $f0, $f0 # negate result 1981: 199 j ra 2007: 201 mtc1 zero, $f0 # result is zero 202 mtc1 zero, $f1 203 beq t0, zero, 1f # is result positive? 204 neg.d $f0, $f0 # negate result 2051: 206 j ra 2078: 208 li t1, 0x7ff00000 # result is infinity (MSW) 209 mtc1 t1, $f1 210 mtc1 zero, $f0 # result is infinity (LSW) 211 bge v1, zero, 1f # should result be negative infinity? 212 neg.d $f0, $f0 # result is negative infinity 2131: 214 add.d $f0, $f0 # cause overflow faults if enabled 215 j ra 2169: 217 mov.d $f0, $f12 # yes, result is just x 218 j ra 219END(ldexp) 220