xref: /netbsd-src/sys/arch/powerpc/fpu/fpu_explode.c (revision f3f59a5d73377b6bc2dcec0001b2faf23b9d3145)

/*	$NetBSD: fpu_explode.c,v 1.14 2022/09/07 06:51:58 rin Exp $ */

/*
 * Copyright (c) 1992, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This software was developed by the Computer Systems Engineering group
 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
 * contributed to Berkeley.
 *
 * All advertising materials mentioning features or use of this software
 * must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Lawrence Berkeley Laboratory.
 *
 * 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.
 *
 *	@(#)fpu_explode.c	8.1 (Berkeley) 6/11/93
 */

/*
 * FPU subroutines: `explode' the machine's `packed binary' format numbers
 * into our internal format.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: fpu_explode.c,v 1.14 2022/09/07 06:51:58 rin Exp $");

#include <sys/types.h>
#include <sys/systm.h>

#include <powerpc/instr.h>
#include <machine/fpu.h>
#include <machine/ieee.h>
#include <machine/reg.h>

#include <powerpc/fpu/fpu_arith.h>
#include <powerpc/fpu/fpu_emu.h>
#include <powerpc/fpu/fpu_extern.h>

static int fpu_itof(struct fpn *, u_int);
static int fpu_xtof(struct fpn *, uint64_t);
static int fpu_stof(struct fpn *, u_int);
static int fpu_dtof(struct fpn *, u_int, u_int);

/*
 * N.B.: in all of the following, we assume the FP format is
 *
 *	---------------------------
 *	| s | exponent | fraction |
 *	---------------------------
 *
 * (which represents -1**s * 1.fraction * 2**exponent), so that the
 * sign bit is way at the top (bit 31), the exponent is next, and
 * then the remaining bits mark the fraction.  A zero exponent means
 * zero or denormalized (0.fraction rather than 1.fraction), and the
 * maximum possible exponent, 2bias+1, signals inf (fraction==0) or NaN.
 *
 * Since the sign bit is always the topmost bit---this holds even for
 * integers---we set that outside all the *tof functions.  Each function
 * returns the class code for the new number (but note that we use
 * FPC_QNAN for all NaNs; fpu_explode will fix this if appropriate).
 */

/*
 * int -> fpn.
 */
static int
fpu_itof(struct fpn *fp, u_int lo)
{

	if (lo == 0)
		return (FPC_ZERO);
	/*
	 * The value FP_1 represents 2^FP_LG, so set the exponent
	 * there and let normalization fix it up.  Convert negative
	 * numbers to sign-and-magnitude.  Note that this relies on
	 * fpu_norm()'s handling of `supernormals'; see fpu_subr.c.
	 */
	fp->fp_exp = FP_LG;
	fp->fp_mant[0] = (int)lo < 0 ? -lo : lo;
	fp->fp_mant[1] = 0;
	fp->fp_mant[2] = 0;
	fp->fp_mant[3] = 0;
	fpu_norm(fp);
	return (FPC_NUM);
}

/*
 * 64-bit int -> fpn.
 */
static int
fpu_xtof(struct fpn *fp, uint64_t i)
{

	if (i == 0)
		return (FPC_ZERO);
	/*
	 * The value FP_1 represents 2^FP_LG, so set the exponent
	 * there and let normalization fix it up.  Convert negative
	 * numbers to sign-and-magnitude.  Note that this relies on
	 * fpu_norm()'s handling of `supernormals'; see fpu_subr.c.
	 */
	fp->fp_exp = FP_LG2;
	*((int64_t*)fp->fp_mant) = (int64_t)i < 0 ? -i : i;
	fp->fp_mant[2] = 0;
	fp->fp_mant[3] = 0;
	fpu_norm(fp);
	return (FPC_NUM);
}

#define	mask(nbits) ((1L << (nbits)) - 1)

/*
 * All external floating formats convert to internal in the same manner,
 * as defined here.  Note that only normals get an implied 1.0 inserted.
 */
#define	FP_TOF(exp, expbias, allfrac, f0, f1, f2, f3) \
	if (exp == 0) { \
		if (allfrac == 0) \
			return (FPC_ZERO); \
		fp->fp_exp = 1 - expbias; \
		fp->fp_mant[0] = f0; \
		fp->fp_mant[1] = f1; \
		fp->fp_mant[2] = f2; \
		fp->fp_mant[3] = f3; \
		fpu_norm(fp); \
		return (FPC_NUM); \
	} \
	if (exp == (2 * expbias + 1)) { \
		if (allfrac == 0) \
			return (FPC_INF); \
		fp->fp_mant[0] = f0; \
		fp->fp_mant[1] = f1; \
		fp->fp_mant[2] = f2; \
		fp->fp_mant[3] = f3; \
		return (FPC_QNAN); \
	} \
	fp->fp_exp = exp - expbias; \
	fp->fp_mant[0] = FP_1 | f0; \
	fp->fp_mant[1] = f1; \
	fp->fp_mant[2] = f2; \
	fp->fp_mant[3] = f3; \
	return (FPC_NUM)

/*
 * 32-bit single precision -> fpn.
 * We assume a single occupies at most (64-FP_LG) bits in the internal
 * format: i.e., needs at most fp_mant[0] and fp_mant[1].
 */
static int
fpu_stof(struct fpn *fp, u_int hi)
{
	int exp;
	u_int frac, f0, f1;
#define SNG_SHIFT (SNG_FRACBITS - FP_LG)

	exp = (hi >> (32 - 1 - SNG_EXPBITS)) & mask(SNG_EXPBITS);
	frac = hi & mask(SNG_FRACBITS);
	f0 = frac >> SNG_SHIFT;
	f1 = frac << (32 - SNG_SHIFT);
	FP_TOF(exp, SNG_EXP_BIAS, frac, f0, f1, 0, 0);
}

/*
 * 64-bit double -> fpn.
 * We assume this uses at most (96-FP_LG) bits.
 */
static int
fpu_dtof(struct fpn *fp, u_int hi, u_int lo)
{
	int exp;
	u_int frac, f0, f1, f2;
#define DBL_SHIFT (DBL_FRACBITS - 32 - FP_LG)

	exp = (hi >> (32 - 1 - DBL_EXPBITS)) & mask(DBL_EXPBITS);
	frac = hi & mask(DBL_FRACBITS - 32);
	f0 = frac >> DBL_SHIFT;
	f1 = (frac << (32 - DBL_SHIFT)) | (lo >> DBL_SHIFT);
	f2 = lo << (32 - DBL_SHIFT);
	frac |= lo;
	FP_TOF(exp, DBL_EXP_BIAS, frac, f0, f1, f2, 0);
}

/*
 * Explode the contents of a register / regpair / regquad.
 * If the input is a signalling NaN, an NV (invalid) exception
 * will be set.  (Note that nothing but NV can occur until ALU
 * operations are performed.)
 */
void
fpu_explode(struct fpemu *fe, struct fpn *fp, int type, uint64_t i)
{
	u_int hi, lo;
	int class;

	hi = (u_int)(i >> 32);
	lo = (u_int)i;
	fp->fp_sign = hi >> 31;
	fp->fp_sticky = 0;
	switch (type) {

	case FTYPE_LNG:
		class = fpu_xtof(fp, i);
		break;

	case FTYPE_INT:
		fp->fp_sign = lo >> 31;
		class = fpu_itof(fp, lo);
		break;

	case FTYPE_SNG:
		class = fpu_stof(fp, hi);
		break;

	case FTYPE_DBL:
		class = fpu_dtof(fp, hi, lo);
		break;

	default:
		panic("fpu_explode: invalid type %d", type);
	}

	if (class == FPC_QNAN && (fp->fp_mant[0] & FP_QUIETBIT) == 0) {
		/*
		 * Input is a signalling NaN.  All operations that return
		 * an input NaN operand put it through a ``NaN conversion'',
		 * which basically just means ``turn on the quiet bit''.
		 * We do this here so that all NaNs internally look quiet
		 * (we can tell signalling ones by their class).
		 */
		fp->fp_mant[0] |= FP_QUIETBIT;
		fe->fe_cx = FPSCR_VXSNAN;	/* assert invalid operand */
		class = FPC_SNAN;
	}
	fp->fp_class = class;
	DUMPFPN(FPE_REG, fp);
}