/* $OpenBSD: ldexp.S,v 1.9 2019/01/05 12:16:59 visa 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 "SYS.h"

#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     63 - 52
#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, 0)
        .set    reorder
        dmfc1   t3, $f12                # get x
        dsll    t1, t3, 1               # get x exponent
        dsrl    t1, t1, 64 - 11
        beq     t1, DEXP_INF, 9f        # is it a NAN or infinity?
        beq     t1, zero, 1f            # zero or denormalized number?
        daddu   t1, a1                  # scale exponent
        dsll    v0, a1, 52              # position N for addition
        bge     t1, DEXP_INF, 8f        # overflow?
        daddu   v0, t3, v0              # multiply by (2**N)
        ble     t1, zero, 4f            # underflow?
        dmtc1   v0, $f0                 # save result
        j       ra
1:
        dsll    t2, t3, 64 - 52         # get x fraction
        dsrl    t2, t2, 64 - 52
        dsrl    t0, t3, 63              # get x sign
        beq     t2, zero, 9f            # result is zero
/*
 * Find out how many leading zero bits are in t2 and put in t9.
 */
        move    v0, t2
        move    t9, zero
        dsrl    ta0, v0, 32
        bne     ta0, zero, 1f
        daddu   t9, 32
        dsll    v0, 32
1:
        dsrl    ta0, v0, 16
        bne     ta0, zero, 1f
        daddu   t9, 16
        dsll    v0, 16
1:
        dsrl    ta0, v0, 24
        bne     ta0, zero, 1f
        daddu   t9, 8
        dsll    v0, 8
1:
        dsrl    ta0, v0, 28
        bne     ta0, zero, 1f
        daddu   t9, 4
        dsll    v0, 4
1:
        dsrl    ta0, v0, 30
        bne     ta0, zero, 1f
        daddu   t9, 2
        dsll    v0, 2
1:
        dsrl    ta0, v0, 31
        bne     ta0, zero, 1f
        daddu   t9, 1
/*
 * Now shift t2 the correct number of bits.
 */
1:
        dsubu   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
        dsll    t2, t9

        bge     t1, DEXP_INF, 8f        # overflow?
        ble     t1, zero, 4f            # underflow?
        dsll    t2, t2, 64 - 52         # clear implied one bit
        dsrl    t2, t2, 64 - 52

        dsll    t1, t1, 63 - 11         # reposition exponent
        dsll    t0, t0, 63              # reposition sign
        or      t0, t0, t1              # put result back together
        or      t0, t0, t2
        dmtc1   t0, $f0                 # save result
        j       ra
4:
        dli     v0, 0x8000000000000000
        ble     t1, -52, 7f             # is result too small for denorm?
        dsll    t2, t3, 63 - 52         # clear exponent, extract fraction
        or      t2, t2, v0              # set implied one bit
        dsrl    t2, t2, 63 - 52         # shift fraction back to normal position
        subu    t1, t1, 1
        dsrl    t8, t2, t1              # save bits shifted out
        negu    t1
        dsrl    t2, t2, t1
        bge     t8, zero, 1f            # does result need to be rounded?
        daddu   t2, t2, 1               # round result
        dsll    t8, t8, 1
        bne     t8, zero, 1f            # round result to nearest
        ori     t2, 1
        xori    t2, 1
1:
        dmtc1   t2, $f0                 # save denormalized result (LSW)
        bge     t3, zero, 1f            # should result be negative?
        neg.d   $f0, $f0                # negate result
1:
        j       ra
7:
        dmtc1   zero, $f0               # result is zero
        bge     t3, zero, 1f            # is result positive?
        neg.d   $f0, $f0                # negate result
1:
        j       ra
8:
        dli     t1, 0x7ff0000000000000  # result is infinity (MSW)
        dmtc1   t1, $f0 
        bge     t3, zero, 1f            # should result be negative infinity?
        neg.d   $f0, $f0                # result is negative infinity
1:
        add.d   $f0, $f0, $f0           # cause overflow faults if enabled
        j       ra
9:
        mov.d   $f0, $f12               # yes, result is just x
        j       ra
END_STRONG(ldexp)