/* $NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc Exp $ */ /*- * Copyright (c) 1991, 1993 * The Regents of the University of California. All rights reserved. * * This code is derived from software contributed to Berkeley by * Ralph Campbell. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include __FBSDID("$FreeBSD$"); #if defined(LIBC_SCCS) && !defined(lint) ASMSTR("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93") ASMSTR("$NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc Exp $") #endif /* LIBC_SCCS and not lint */ #ifdef __ABICALLS__ .abicalls #endif #define DEXP_INF 0x7ff #define DEXP_BIAS 1023 #define DEXP_MIN -1022 #define DEXP_MAX 1023 #define DFRAC_BITS 52 #define DIMPL_ONE 0x00100000 #define DLEAD_ZEROS 31 - 20 #define STICKYBIT 1 #define GUARDBIT 0x80000000 #define DSIGNAL_NAN 0x00040000 #define DQUIET_NAN0 0x0007ffff #define DQUIET_NAN1 0xffffffff /* * double ldexp(x, N) * double x; int N; * * Return x * (2**N), for integer values N. */ LEAF(ldexp) mfc1 v1, $f13 # get MSW of x mfc1 t3, $f12 # get LSW of x sll t1, v1, 1 # get x exponent srl t1, t1, 32 - 11 beq t1, DEXP_INF, 9f # is it a NAN or infinity? beq t1, zero, 1f # zero or denormalized number? addu t1, t1, a2 # scale exponent sll v0, a2, 20 # position N for addition bge t1, DEXP_INF, 8f # overflow? addu v0, v0, v1 # multiply by (2**N) ble t1, zero, 4f # underflow? mtc1 v0, $f1 # save MSW of result mtc1 t3, $f0 # save LSW of result j ra 1: sll t2, v1, 32 - 20 # get x fraction srl t2, t2, 32 - 20 srl t0, v1, 31 # get x sign bne t2, zero, 1f beq t3, zero, 9f # result is zero 1: /* * Find out how many leading zero bits are in t2,t3 and put in t9. */ move v0, t2 move t9, zero bne t2, zero, 1f move v0, t3 addu t9, 32 1: srl ta0, v0, 16 bne ta0, zero, 1f addu t9, 16 sll v0, 16 1: srl ta0, v0, 24 bne ta0, zero, 1f addu t9, 8 sll v0, 8 1: srl ta0, v0, 28 bne ta0, zero, 1f addu t9, 4 sll v0, 4 1: srl ta0, v0, 30 bne ta0, zero, 1f addu t9, 2 sll v0, 2 1: srl ta0, v0, 31 bne ta0, zero, 1f addu t9, 1 /* * Now shift t2,t3 the correct number of bits. */ 1: subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros li t1, DEXP_MIN + DEXP_BIAS subu t1, t1, t9 # adjust exponent addu t1, t1, a2 # scale exponent li v0, 32 blt t9, v0, 1f subu t9, t9, v0 # shift fraction left >= 32 bits sll t2, t3, t9 move t3, zero b 2f 1: subu v0, v0, t9 # shift fraction left < 32 bits sll t2, t2, t9 srl ta0, t3, v0 or t2, t2, ta0 sll t3, t3, t9 2: bge t1, DEXP_INF, 8f # overflow? ble t1, zero, 4f # underflow? sll t2, t2, 32 - 20 # clear implied one bit srl t2, t2, 32 - 20 3: sll t1, t1, 31 - 11 # reposition exponent sll t0, t0, 31 # reposition sign or t0, t0, t1 # put result back together or t0, t0, t2 mtc1 t0, $f1 # save MSW of result mtc1 t3, $f0 # save LSW of result j ra 4: li v0, 0x80000000 ble t1, -52, 7f # is result too small for denorm? sll t2, v1, 31 - 20 # clear exponent, extract fraction or t2, t2, v0 # set implied one bit blt t1, -30, 2f # will all bits in t3 be shifted out? srl t2, t2, 31 - 20 # shift fraction back to normal position subu t1, t1, 1 sll ta0, t2, t1 # shift right t2,t3 based on exponent srl t8, t3, t1 # save bits shifted out negu t1 srl t3, t3, t1 or t3, t3, ta0 srl t2, t2, t1 bge t8, zero, 1f # does result need to be rounded? addu t3, t3, 1 # round result sltu ta0, t3, 1 sll t8, t8, 1 addu t2, t2, ta0 bne t8, zero, 1f # round result to nearest and t3, t3, ~1 1: mtc1 t3, $f0 # save denormalized result (LSW) mtc1 t2, $f1 # save denormalized result (MSW) bge v1, zero, 1f # should result be negative? neg.d $f0, $f0 # negate result 1: j ra 2: mtc1 zero, $f1 # exponent and upper fraction addu t1, t1, 20 # compute amount to shift right by sll t8, t2, t1 # save bits shifted out negu t1 srl t3, t2, t1 bge t8, zero, 1f # does result need to be rounded? addu t3, t3, 1 # round result sltu ta0, t3, 1 sll t8, t8, 1 mtc1 ta0, $f1 # exponent and upper fraction bne t8, zero, 1f # round result to nearest and t3, t3, ~1 1: mtc1 t3, $f0 bge v1, zero, 1f # is result negative? neg.d $f0, $f0 # negate result 1: j ra 7: mtc1 zero, $f0 # result is zero mtc1 zero, $f1 beq t0, zero, 1f # is result positive? neg.d $f0, $f0 # negate result 1: j ra 8: li t1, 0x7ff00000 # result is infinity (MSW) mtc1 t1, $f1 mtc1 zero, $f0 # result is infinity (LSW) bge v1, zero, 1f # should result be negative infinity? neg.d $f0, $f0 # result is negative infinity 1: add.d $f0, $f0 # cause overflow faults if enabled j ra 9: mov.d $f0, $f12 # yes, result is just x j ra END(ldexp)