simh-testsetgenerator/PDP11/pdp11_fp.c

/* pdp11_fp.c: PDP-11 floating point simulator (32b version)

   Copyright (c) 1993-2004, Robert M Supnik

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   ROBERT M SUPNIK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

   Except as contained in this notice, the name of Robert M Supnik shall not
   be used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from Robert M Supnik.

   04-Oct-04	RMS	Added FIS instructions
   19-Jan-03	RMS	Changed mode definitions for Apple Dev Kit conflict
   08-Oct-02	RMS	Fixed macro definitions
   05-Jun-98	RMS	Fixed implementation specific shift bugs
   20-Apr-98	RMS	Fixed bug in MODf integer truncation
   17-Apr-98	RMS	Fixed bug in STCfi range check
   16-Apr-98	RMS	Fixed bugs in STEXP, STCfi, round/pack
   09-Apr-98	RMS	Fixed bug in LDEXP
   04-Apr-98	RMS	Fixed bug in MODf condition codes
	
   This module simulates the PDP-11 floating point unit (FP11 series).
   It is called from the instruction decoder for opcodes 170000:177777.

   The floating point unit recognizes three instruction formats:

   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	no operand
   | 1  1  1  1| 0  0  0  0  0  0|      opcode     |	170000:
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	170077

   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	one operand
   | 1  1  1  1| 0  0  0| opcode |    dest spec    |	170100:
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	170777

   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	register + operand
   | 1  1  1  1|   opcode  | fac |    dest spec    |	171000:
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+	177777

   The instruction space is further extended through use of the floating
   point status register (FPS) mode bits.  Three mode bits affect how
   instructions are interpreted:

	FPS_D		if 0, floating registers are single precision
			if 1, floating registers are double precision

	FPS_L		if 0, integer operands are word
			if 1, integer operands are longword

	FPS_T		if 0, floating operations are rounded
			if 1, floating operations are truncated

   FPS also contains the condition codes for the floating point unit,
   and exception enable bits for individual error conditions.  Exceptions
   cause a trap through 0244, unless the individual exception, or all
   exceptions, are disabled.  Illegal address mode, undefined variable,
   and divide by zero abort the current instruction; all other exceptions
   permit the instruction to complete.  (Aborts are implemented as traps
   that request an "interrupt" trap.  If an interrupt is pending, it is
   serviced; if not, trap_req is updated and processing continues.)

   Floating point specifiers are similar to integer specifiers, with
   the length of the operand being up to 8 bytes.  In two specific cases,
   the floating point unit reads or writes only two bytes, rather than
   the length specified by the operand type:

	register	for integers, only 16b are accessed; if the
			operand is 32b, these are the high order 16b
			of the operand

	immediate	for integers or floating point, only 16b are
			accessed;  if the operand is 32b or 64b, these
			are the high order 16b of the operand
*/

#include "pdp11_defs.h"

/* Floating point status register */

#define FPS_ER		(1u << FPS_V_ER)		/* error */
#define FPS_ID		(1u << FPS_V_ID)		/* interrupt disable */
#define FPS_IUV		(1u << FPS_V_IUV)		/* int on undef var */
#define FPS_IU		(1u << FPS_V_IU)		/* int on underflow */
#define FPS_IV		(1u << FPS_V_IV)		/* int on overflow */
#define FPS_IC		(1u << FPS_V_IC)		/* int on conv error */
#define FPS_D		(1u << FPS_V_D)			/* single/double */
#define FPS_L		(1u << FPS_V_L)			/* word/long */
#define FPS_T		(1u << FPS_V_T)			/* round/truncate */
#define FPS_N		(1u << FPS_V_N)
#define FPS_Z		(1u << FPS_V_Z)
#define FPS_V		(1u << FPS_V_V)
#define FPS_C		(1u << FPS_V_C)
#define FPS_CC		(FPS_N + FPS_Z + FPS_V + FPS_C)
#define FPS_RW		(FPS_ER + FPS_ID + FPS_IUV + FPS_IU + FPS_IV + \
			FPS_IC + FPS_D + FPS_L + FPS_T + FPS_CC)

/* Floating point exception codes */

#define FEC_OP		2				/* illegal op/mode */
#define FEC_DZRO	4				/* divide by zero */
#define FEC_ICVT	6				/* conversion error */
#define FEC_OVFLO	8				/* overflow */
#define FEC_UNFLO	10				/* underflow */
#define FEC_UNDFV	12				/* undef variable */

/* Floating point format, all assignments 32b relative */

#define FP_V_SIGN	(63 - 32)			/* high lw: sign */
#define FP_V_EXP	(55 - 32)			/* exponent */
#define FP_V_HB		FP_V_EXP			/* hidden bit */
#define FP_V_F0		(48 - 32)			/* fraction 0 */
#define FP_V_F1		(32 - 32)			/* fraction 1 */
#define FP_V_FROUND	(31 - 32)			/* f round point */
#define FP_V_F2		16				/* low lw: fraction 2 */
#define FP_V_F3		0				/* fraction 3 */
#define FP_V_DROUND	(-1)				/* d round point */
#define FP_M_EXP	0377
#define FP_SIGN		(1u << FP_V_SIGN)
#define FP_EXP		(FP_M_EXP << FP_V_EXP)
#define FP_HB		(1u << FP_V_HB)
#define FP_FRACH	((1u << FP_V_HB) - 1)
#define FP_FRACL	0xFFFFFFFF
#define FP_BIAS		0200				/* exponent bias */
#define FP_GUARD	3				/* guard bits */

/* Data lengths */

#define WORD		2
#define LONG		4
#define QUAD		8

/* Double precision operations on 64b quantities */

#define F_LOAD(qd,ac,ds) ds.h = ac.h; ds.l = (qd)? ac.l: 0
#define F_LOAD_P(qd,ac,ds) ds->h = ac.h; ds->l = (qd)? ac.l: 0
#define F_LOAD_FRAC(qd,ac,ds) ds.h = (ac.h & FP_FRACH) | FP_HB; \
	ds.l = (qd)? ac.l: 0
#define F_STORE(qd,sr,ac) ac.h = sr.h; if ((qd)) ac.l = sr.l
#define F_STORE_P(qd,sr,ac) ac.h = sr->h; if ((qd)) ac.l = sr->l
#define F_GET_FRAC_P(sr,ds) ds.l = sr->l; \
	ds.h = (sr->h & FP_FRACH) | FP_HB
#define F_ADD(s2,s1,ds) ds.l = (s1.l + s2.l) & 0xFFFFFFFF; \
	ds.h = (s1.h + s2.h + (ds.l < s2.l)) & 0xFFFFFFFF
#define F_SUB(s2,s1,ds) ds.h = (s1.h - s2.h - (s1.l < s2.l)) & 0xFFFFFFFF; \
	ds.l = (s1.l - s2.l) & 0xFFFFFFFF
#define F_LT(x,y) ((x.h < y.h) || ((x.h == y.h) && (x.l < y.l)))
#define F_LT_AP(x,y) (((x->h & ~FP_SIGN) < (y->h & ~FP_SIGN)) || \
	(((x->h & ~FP_SIGN) == (y->h & ~FP_SIGN)) && (x->l < y->l)))
#define F_LSH_V(sr,n,ds) \
	ds.h = (((n) >= 32)? (sr.l << ((n) - 32)): \
		(sr.h << (n)) | ((sr.l >> (32 - (n))) & and_mask[n])) \
		& 0xFFFFFFFF; \
	ds.l = ((n) >= 32)? 0: (sr.l << (n)) & 0xFFFFFFFF
#define F_RSH_V(sr,n,ds) \
	ds.l = (((n) >= 32)? (sr.h >> ((n) - 32)) & and_mask[64 - (n)]: \
		((sr.l >> (n)) & and_mask[32 - (n)]) | \
		(sr.h << (32 - (n)))) & 0xFFFFFFFF; \
	ds.h = ((n) >= 32)? 0: \
		((sr.h >> (n)) & and_mask[32 - (n)]) & 0xFFFFFFFF

/* For the constant shift macro, arguments must in the range [2,31] */

#define F_LSH_1(ds) ds.h = ((ds.h << 1) | ((ds.l >> 31) & 1)) & 0xFFFFFFFF; \
	ds.l = (ds.l << 1) & 0xFFFFFFFF
#define F_RSH_1(ds) ds.l = ((ds.l >> 1) & 0x7FFFFFFF) | ((ds.h & 1) << 31); \
	ds.h = ((ds.h >> 1) & 0x7FFFFFFF)
#define F_LSH_K(sr,n,ds) \
	ds.h = 	((sr.h << (n)) | ((sr.l >> (32 - (n))) & and_mask[n])) \
		& 0xFFFFFFFF; \
	ds.l = (sr.l << (n)) & 0xFFFFFFFF
#define F_RSH_K(sr,n,ds) \
	ds.l = 	(((sr.l >> (n)) & and_mask[32 - (n)]) | \
		(sr.h << (32 - (n)))) & 0xFFFFFFFF; \
	ds.h = 	((sr.h >> (n)) & and_mask[32 - (n)]) & 0xFFFFFFFF
#define F_LSH_GUARD(ds) F_LSH_K(ds,FP_GUARD,ds)
#define F_RSH_GUARD(ds) F_RSH_K(ds,FP_GUARD,ds)

#define GET_BIT(ir,n)	(((ir) >> (n)) & 1)
#define GET_SIGN(ir)	GET_BIT((ir), FP_V_SIGN)
#define GET_EXP(ir)	(((ir) >> FP_V_EXP) & FP_M_EXP)
#define GET_SIGN_L(ir)	GET_BIT((ir), 31)
#define GET_SIGN_W(ir)	GET_BIT((ir), 15)

extern jmp_buf save_env;
extern int32 cpu_type;
extern int32 FEC, FEA, FPS;
extern int32 CPUERR, trap_req;
extern int32 N, Z, V, C;
extern int32 R[8];
extern int32 STKLIM;
extern int32 cm, isenable, dsenable, MMR0, MMR1;
extern fpac_t FR[6];

fpac_t zero_fac = { 0, 0 };
fpac_t one_fac = { 1, 0 };
fpac_t fround_fac = { (1u << (FP_V_FROUND + 32)), 0 };
fpac_t fround_guard_fac = { 0, (1u << (FP_V_FROUND + FP_GUARD)) };
fpac_t dround_guard_fac = { (1u << (FP_V_DROUND + FP_GUARD)), 0 };
fpac_t fmask_fac = { 0xFFFFFFFF, (1u << (FP_V_HB + FP_GUARD + 1)) - 1 };
static const uint32 and_mask[33] = { 0,
	0x1, 0x3, 0x7, 0xF,
	0x1F, 0x3F, 0x7F, 0xFF,
	0x1FF, 0x3FF, 0x7FF, 0xFFF,
	0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF,
	0x1FFFF, 0x3FFFF, 0x7FFFF, 0xFFFFF,
	0x1FFFFF, 0x3FFFFF, 0x7FFFFF, 0xFFFFFF,
	0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF,
	0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF };
int32 backup_PC;
int32 fpnotrap (int32 code);
int32 GeteaFP (int32 spec, int32 len);

uint32 ReadI (int32 addr, int32 spec, int32 len);
void ReadFP (fpac_t *fac, int32 addr, int32 spec, int32 len);
void WriteI (int32 data, int32 addr, int32 spec, int32 len);
void WriteFP (fpac_t *data, int32 addr, int32 spec, int32 len);
int32 setfcc (int32 old_status, int32 result_high, int32 newV);
int32 addfp11 (fpac_t *src1, fpac_t *src2);
int32 mulfp11 (fpac_t *src1, fpac_t *src2);
int32 divfp11 (fpac_t *src1, fpac_t *src2);
int32 modfp11 (fpac_t *src1, fpac_t *src2, fpac_t *frac);
void frac_mulfp11 (fpac_t *src1, fpac_t *src2);
int32 roundfp11 (fpac_t *src);
int32 round_and_pack (fpac_t *fac, int32 exp, fpac_t *frac, int r);

extern int32 GeteaW (int32 spec);
extern int32 ReadW (int32 addr);
extern void WriteW (int32 data, int32 addr);
extern void set_stack_trap (int32 adr);

/* Set up for instruction decode and execution */

void fp11 (int32 IR)
{
int32 dst, ea, ac, dstspec;
int32 i, qdouble, lenf, leni;
int32 newV, exp, sign;
fpac_t fac, fsrc, modfrac;
static const uint32 i_limit[2][2] =
	{ { 0x80000000, 0x80010000 }, { 0x80000000, 0x80000001 } };

backup_PC = PC;						/* save PC for FEA */
ac = (IR >> 6) & 03;					/* fac is IR<7:6> */
dstspec = IR & 077;
qdouble = FPS & FPS_D;
lenf = qdouble? QUAD: LONG;
switch ((IR >> 8) & 017) {				/* decode IR<11:8> */
case 0:
	switch (ac) {					/* decode IR<7:6> */
	case 0:						/* specials */
	    if (IR == 0170000) {			/* CFCC */
		N = (FPS >> PSW_V_N) & 1;
		Z = (FPS >> PSW_V_Z) & 1;
		V = (FPS >> PSW_V_V) & 1;
		C = (FPS >> PSW_V_C) & 1;  }
	    else if (IR == 0170001)			/* SETF */
		FPS = FPS & ~FPS_D;
	    else if (IR == 0170002)			/* SETI */
		FPS = FPS & ~FPS_L;
	    else if (IR == 0170011)			/* SETD */
		FPS = FPS | FPS_D;
	    else if (IR == 0170012)			/* SETL */
		FPS = FPS | FPS_L;
	    else fpnotrap (FEC_OP);
	    break;
	case 1:						/* LDFPS */
	    dst = (dstspec <= 07)? R[dstspec]: ReadW (GeteaW (dstspec));
	    FPS = dst & FPS_RW;
	    break;
	case 2:						/* STFPS */
	    FPS = FPS & FPS_RW;
	    if (dstspec <= 07) R[dstspec] = FPS;
	    else WriteW (FPS, GeteaW (dstspec));
	    break;
	case 3:						/* STST */
	    if (dstspec <= 07) R[dstspec] = FEC;
	    else WriteI ((FEC << 16) | FEA, GeteaFP (dstspec, LONG),
		 dstspec, LONG);
	    break;  }				/* end switch <7:6> */
	break;						/* end case 0 */

/* "Easy" instructions */

case 1:
	switch (ac) {					/* decode IR<7:6> */
	case 0:						/* CLRf */
	    WriteFP (&zero_fac, GeteaFP (dstspec, lenf), dstspec, lenf);
	    FPS = (FPS & ~FPS_CC) | FPS_Z;
	    break;
	case 1:						/* TSTf */
	    ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	    FPS = setfcc (FPS, fsrc.h, 0);
	    break;
	case 2:						/* ABSf */
	    ReadFP (&fsrc, ea = GeteaFP (dstspec, lenf), dstspec, lenf);
	    if (GET_EXP (fsrc.h) == 0) fsrc = zero_fac;
	    else fsrc.h = fsrc.h & ~FP_SIGN;
	    WriteFP (&fsrc, ea, dstspec, lenf);
	    FPS = setfcc (FPS, fsrc.h, 0);
	    break;
	case 3:						/* NEGf */
	    ReadFP (&fsrc, ea = GeteaFP (dstspec, lenf), dstspec, lenf);
	    if (GET_EXP (fsrc.h) == 0) fsrc = zero_fac;
	    else fsrc.h = fsrc.h ^ FP_SIGN;
	    WriteFP (&fsrc, ea, dstspec, lenf);
	    FPS = setfcc (FPS, fsrc.h, 0);
	    break;  }					/* end switch <7:6> */
	break;						/* end case 1 */
case 5:							/* LDf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_STORE (qdouble, fsrc, FR[ac]);
	FPS = setfcc (FPS, fsrc.h, 0);
	break;
case 010:						/* STf */
	F_LOAD (qdouble, FR[ac], fac);
	WriteFP (&fac, GeteaFP (dstspec, lenf), dstspec, lenf);
	break;
case 017:						/* LDCff' */
	ReadFP (&fsrc, GeteaFP (dstspec, 12 - lenf), dstspec, 12 - lenf);
	if (GET_EXP (fsrc.h) == 0) fsrc = zero_fac;
	if ((FPS & (FPS_D + FPS_T)) == 0) newV = roundfp11 (&fsrc);
	else newV = 0;
	F_STORE (qdouble, fsrc, FR[ac]);
	FPS = setfcc (FPS, fsrc.h, newV);
	break;
case 014:						/* STCff' */
	F_LOAD (qdouble, FR[ac], fac);
	if (GET_EXP (fac.h) == 0) fac = zero_fac;
	if ((FPS & (FPS_D + FPS_T)) == FPS_D) newV = roundfp11 (&fac);
	else newV = 0;
	WriteFP (&fac, GeteaFP (dstspec, 12 - lenf), dstspec, 12 - lenf);
	FPS = setfcc (FPS, fac.h, newV);
	break;

/* Compare instruction */

case 7:							/* CMPf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	if (GET_EXP (fsrc.h) == 0) fsrc = zero_fac;
	if (GET_EXP (fac.h) == 0) fac = zero_fac;
	if ((fsrc.h == fac.h) && (fsrc.l == fac.l)) {	/* equal? */
	    FPS = (FPS & ~FPS_CC) | FPS_Z;
	    if ((fsrc.h | fsrc.l) == 0) {		/* zero? */
		F_STORE (qdouble, zero_fac, FR[ac]);  }
	    break;  }
	FPS = (FPS & ~FPS_CC) | ((fsrc.h >> (FP_V_SIGN - PSW_V_N)) & FPS_N);
	if ((GET_SIGN (fsrc.h ^ fac.h) == 0) && (fac.h != 0) &&
	    F_LT (fsrc, fac)) FPS = FPS ^ FPS_N;
	break;

/* Load and store exponent instructions */

case 015:						/* LDEXP */
	dst = (dstspec <= 07)? R[dstspec]: ReadW (GeteaW (dstspec));
	F_LOAD (qdouble, FR[ac], fac);
	fac.h = (fac.h & ~FP_EXP) | (((dst + FP_BIAS) & FP_M_EXP) << FP_V_EXP);
	newV = 0;
	if ((dst > 0177) && (dst <= 0177600)) {
	    if (dst < 0100000) {
		if (fpnotrap (FEC_OVFLO)) fac = zero_fac;
		newV = FPS_V;  }
	    else {
	    	if (fpnotrap (FEC_UNFLO)) fac = zero_fac;  }  }
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, newV);
	break;	
case 012:						/* STEXP */
	dst = (GET_EXP (FR[ac].h) - FP_BIAS) & 0177777;
	N = GET_SIGN_W (dst);
	Z = (dst == 0);
	V = 0;
	C = 0;
	FPS = (FPS & ~FPS_CC) | (N << PSW_V_N) | (Z << PSW_V_Z);
	if (dstspec <= 07) R[dstspec] = dst;
	else WriteW (dst, GeteaW (dstspec));
	break;

/* Integer convert instructions */

case 016:						/* LDCif */
	leni = FPS & FPS_L? LONG: WORD;
	if (dstspec <= 07) fac.l = R[dstspec] << 16;
	else fac.l = ReadI (GeteaFP (dstspec, leni), dstspec, leni);
	fac.h = 0;
	if (fac.l) {
	    if (sign = GET_SIGN_L (fac.l)) fac.l = (fac.l ^ 0xFFFFFFFF) + 1;
	    for (i = 0; GET_SIGN_L (fac.l) == 0; i++) fac.l = fac.l << 1;
	    exp = ((FPS & FPS_L)? FP_BIAS + 32: FP_BIAS + 16) - i;
	    fac.h = (sign << FP_V_SIGN) | (exp << FP_V_EXP) |
		((fac.l >> (31 - FP_V_HB)) & FP_FRACH);
	    fac.l = (fac.l << (FP_V_HB + 1)) & FP_FRACL;
	    if ((FPS & (FPS_D + FPS_T)) == 0) roundfp11 (&fac);  }
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, 0);
	break;
case 013:						/* STCfi */
	sign = GET_SIGN (FR[ac].h);			/* get sign, */
	exp = GET_EXP (FR[ac].h);			/* exponent, */
	F_LOAD_FRAC (qdouble, FR[ac], fac);		/* fraction */
	if (FPS & FPS_L) {
	    leni = LONG;
	    i = FP_BIAS + 32;  }
	else {
	    leni = WORD;
	    i = FP_BIAS + 16;  }
	C = 0;
	if (exp <= FP_BIAS) dst = 0;
	else if (exp > i) {
	    dst = 0;
	    C = 1;  }
	else {
	    F_RSH_V (fac, FP_V_HB + 1 + i - exp, fsrc);
	    if (leni == WORD) fsrc.l = fsrc.l & ~0177777;
	    if (fsrc.l >= i_limit[leni == LONG][sign]) {
		dst = 0;
		C = 1;  }  
	    else {
	    	dst = fsrc.l;
		if (sign) dst = -dst;  }  }
	N = GET_SIGN_L (dst);
	Z = (dst == 0);
	V = 0;
	if (C) fpnotrap (FEC_ICVT);
	FPS = (FPS & ~FPS_CC) | (N << PSW_V_N) |
	    (Z << PSW_V_Z) | (C << PSW_V_C);
	if (dstspec <= 07) R[dstspec] = (dst >> 16) & 0177777;
	else WriteI (dst, GeteaFP (dstspec, leni), dstspec, leni);
	break;

/* Calculation instructions */

case 2:							/* MULf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	newV = mulfp11 (&fac, &fsrc);
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, newV);
	break;
case 3:							/* MODf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	newV = modfp11 (&fac, &fsrc, &modfrac);
	F_STORE (qdouble, fac, FR[ac | 1]);
	F_STORE (qdouble, modfrac, FR[ac]);
	FPS = setfcc (FPS, modfrac.h, newV);
	break;
case 4:							/* ADDf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	newV = addfp11 (&fac, &fsrc);
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, newV);
	break;
case 6:							/* SUBf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	if (GET_EXP (fsrc.h) != 0) fsrc.h = fsrc.h ^ FP_SIGN;
	newV = addfp11 (&fac, &fsrc);
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, newV);
	break;
case 011:						/* DIVf */
	ReadFP (&fsrc, GeteaFP (dstspec, lenf), dstspec, lenf);
	F_LOAD (qdouble, FR[ac], fac);
	if (GET_EXP (fsrc.h) == 0) {			/* divide by zero? */
	    fpnotrap (FEC_DZRO);
	    ABORT (TRAP_INT);  }
	newV = divfp11 (&fac, &fsrc);
	F_STORE (qdouble, fac, FR[ac]);
	FPS = setfcc (FPS, fac.h, newV);
	break;  }					/* end switch fop */
return;
}

/* Effective address calculation for fp operands

   Inputs:
	spec	=	specifier
	len	=	length
   Outputs:
	VA	=	virtual address

   Warnings:
	- Do not call this routine for integer mode 0 operands
	- Do not call this routine more than once per instruction
*/

int32 GeteaFP (int32 spec, int32 len)
{
int32 adr, reg, ds;

reg = spec & 07;					/* reg number */
ds = (reg == 7)? isenable: dsenable;			/* dspace if not PC */
switch (spec >> 3) {					/* case on spec */
case 0:							/* floating AC */
	if (reg >= 06) { fpnotrap (FEC_OP); ABORT (TRAP_INT);  }
	return 0;
case 1:							/* (R) */
	return (R[reg] | ds);
case 2:							/* (R)+ */
	if (reg == 7) len = 2;
	R[reg] = ((adr = R[reg]) + len) & 0177777;
	if (update_MM) MMR1 = (len << 3) | reg;
	return (adr | ds);
case 3:							/* @(R)+ */
	R[reg] = ((adr = R[reg]) + 2) & 0177777;
	if (update_MM) MMR1 = 020 | reg;
	adr = ReadW (adr | ds);
	return (adr | dsenable);
case 4:							/* -(R) */
	adr = R[reg] = (R[reg] - len) & 0177777;
	if (update_MM) MMR1 = (((-len) & 037) << 3) | reg;
	if ((reg == 6) && (cm == MD_KER) && (adr < (STKLIM + STKL_Y)))
	    set_stack_trap (adr);
	return (adr | ds);
case 5:							/* @-(R) */
	adr = R[reg] = (R[reg] - 2) & 0177777;
	if (update_MM) MMR1 = 0360 | reg;
	if ((reg == 6) && (cm == MD_KER) && (adr < (STKLIM + STKL_Y)))
	    set_stack_trap (adr);
	adr = ReadW (adr | ds);
	return (adr | dsenable);
case 6:							/* d(r) */
	adr = ReadW (PC | isenable);
	PC = (PC + 2) & 0177777;
	return (((R[reg] + adr) & 0177777) | dsenable);
case 7:							/* @d(R) */
	adr = ReadW (PC | isenable);
	PC = (PC + 2) & 0177777;
	adr = ReadW (((R[reg] + adr) & 0177777) | dsenable);
	return (adr | dsenable);  }			/* end switch */
return 0;
}

/* Read integer operand

   Inputs:
	VA	=	virtual address, VA<18:16> = mode, I/D space
	spec	=	specifier
	len	=	length (2/4 bytes)
   Outputs:
	data	=	data read from memory or I/O space
*/

uint32 ReadI (int32 VA, int32 spec, int32 len)
{
if ((len == WORD) || (spec == 027)) return (ReadW (VA) << 16);
return ((ReadW (VA) << 16) | ReadW ((VA & ~0177777) | ((VA + 2) & 0177777)));
}

/* Read floating operand

   Inputs:
	fptr	=	pointer to output
	VA	=	virtual address, VA<18:16> = mode, I/D space
	spec	=	specifier
	len	=	length (4/8 bytes)
*/

void ReadFP (fpac_t *fptr, int32 VA, int32 spec, int32 len)
{
int32 exta;

if (spec <= 07) {
	F_LOAD_P (len == QUAD, FR[spec], fptr);
	return;  }
if (spec == 027) {
	fptr->h = (ReadW (VA) << FP_V_F0);
	fptr->l = 0;  }
else {	exta = VA & ~0177777;
	fptr->h = (ReadW (VA) << FP_V_F0) |
	    (ReadW (exta | ((VA + 2) & 0177777)) << FP_V_F1);
	if (len == QUAD) fptr->l = 
	    (ReadW (exta | ((VA + 4) & 0177777)) << FP_V_F2) |
	    (ReadW (exta | ((VA + 6) & 0177777)) << FP_V_F3);
	else fptr->l = 0;  }
if ((GET_SIGN (fptr->h) != 0) && (GET_EXP (fptr->h) == 0) &&
	(fpnotrap (FEC_UNDFV) == 0)) ABORT (TRAP_INT);
return;
}

/* Write integer result

   Inputs:
	data	=	data to be written
	VA	=	virtual address, VA<18:16> = mode, I/D space
	spec	=	specifier
	len	=	length
   Outputs: none
*/

void WriteI (int32 data, int32 VA, int32 spec, int32 len)
{
WriteW ((data >> 16) & 0177777, VA);
if ((len == WORD) || (spec == 027)) return;
WriteW (data & 0177777, (VA & ~0177777) | ((VA + 2) & 0177777));
return;
}

/* Write floating result

   Inputs:
	fptr	=	pointer to data to be written
	VA	=	virtual address, VA<18:16> = mode, I/D space
	spec	=	specifier
	len	=	length
   Outputs: none
*/

void WriteFP (fpac_t *fptr, int32 VA, int32 spec, int32 len)
{
int32 exta;

if (spec <= 07) {
	F_STORE_P (len == QUAD, fptr, FR[spec]);
	return;  }
WriteW ((fptr->h >> FP_V_F0) & 0177777, VA);
if (spec == 027) return;
exta = VA & ~0177777;
WriteW ((fptr->h >> FP_V_F1) & 0177777, exta | ((VA + 2) & 0177777));
if (len == LONG) return;
WriteW ((fptr->l >> FP_V_F2) & 0177777, exta | ((VA + 4) & 0177777));
WriteW ((fptr->l >> FP_V_F3) & 0177777, exta | ((VA + 6) & 0177777));
return;
}

/* FIS instructions */

t_stat fis11 (int32 IR)
{
int32 reg, exta;
fpac_t fac, fsrc;

reg = IR & 07;						/* isolate reg */
if (reg == 7) exta = isenable;				/* choose I,D */
else exta = dsenable;
if (IR & 000740) {					/* defined? */
	if (CPUT (CPUT_03)) ReadW (exta | R[reg]);	/* 11/03 reads word */
	ABORT (TRAP_ILL);  }
FEC = 0;						/* no errors */
FPS = FPS_IU|FPS_IV;					/* trap ovf,unf */

fsrc.h = (ReadW (exta | R[reg]) << FP_V_F0) |
	(ReadW (exta | ((R[reg] + 2) & 0177777)) << FP_V_F1);
fsrc.l = 0;
fac.h = (ReadW (exta | ((R[reg] + 4) & 0177777)) << FP_V_F0) |
	(ReadW (exta | ((R[reg] + 6) & 0177777)) << FP_V_F1);
fac.l = 0;
if (GET_SIGN (fsrc.h) && (GET_EXP (fsrc.h) == 0))	/* clean 0's */
	fsrc.h = fsrc.l = 0;
if (GET_SIGN (fac.h) && (GET_EXP (fac.l) == 0))
	fac.h = fac.l = 0;

N = Z = V = C = 0;					/* clear cc's */
switch ((IR >> 3) & 3) {				/* case IR<5:3> */

case 0:							/* FAD */
	addfp11 (&fac, &fsrc);
	break;
case 1:							/* FSUB */
	if (fsrc.h != 0) fsrc.h = fsrc.h ^ FP_SIGN;	/* invert sign */
	addfp11 (&fac, &fsrc);
	break;
case 2:							/* FMUL */
	mulfp11 (&fac, &fsrc);
	break;
case 3:							/* FDIV */
	if (fsrc.h == 0) {				/* div by 0? */
	    V = N = C = 1;				/* set cc's */
	    setTRAP (TRAP_FPE);				/* set trap */
	    return SCPE_OK;  }
	else divfp11 (&fac, &fsrc);
	break;  }

if (FEC == 0) {						/* no err? */
	WriteW ((fac.h >> FP_V_F0) & 0177777, exta | ((R[reg] + 4) & 0177777));
	WriteW ((fac.h >> FP_V_F1) & 0177777, exta | ((R[reg] + 6) & 0177777));
	R[reg] = (R[reg] + 4) & 0177777;		/* pop stack */
	N = (GET_SIGN (fac.h) != 0);			/* set N,Z */
	Z = (fac.h == 0);  }
else if (FEC == FEC_OVFLO) V = 1;			/* ovf? trap set */
else if (FEC == FEC_UNFLO) V = N = 1;			/* unf? trap set */
else return SCPE_IERR;					/* what??? */
return SCPE_OK;
}

/* Floating point add

   Inputs:
	facp	=	pointer to src1 (output)
	fsrcp	=	pointer to src2
   Outputs:
	ovflo	=	overflow variable
*/

int32 addfp11 (fpac_t *facp, fpac_t *fsrcp)
{
int32 facexp, fsrcexp, ediff;
fpac_t facfrac, fsrcfrac;

if (F_LT_AP (facp, fsrcp)) {				/* if !fac! < !fsrc! */
	facfrac = *facp;
	*facp = *fsrcp;					/* swap operands */
	*fsrcp = facfrac;  }
facexp = GET_EXP (facp->h);				/* get exponents */
fsrcexp = GET_EXP (fsrcp->h);
if (facexp == 0) {					/* fac = 0? */
	*facp = fsrcexp? *fsrcp: zero_fac;		/* result fsrc or 0 */
	return 0;  }
if (fsrcexp == 0) return 0;				/* fsrc = 0? no op */
ediff = facexp - fsrcexp;				/* exponent diff */
if (ediff >= 60) return 0;				/* too big? no op */
F_GET_FRAC_P (facp, facfrac);				/* get fractions */
F_GET_FRAC_P (fsrcp, fsrcfrac);
F_LSH_GUARD (facfrac);					/* guard fractions */
F_LSH_GUARD (fsrcfrac);
if (GET_SIGN (facp->h) != GET_SIGN (fsrcp->h)) {	/* signs different? */
	if (ediff) { F_RSH_V (fsrcfrac, ediff, fsrcfrac);  } /* sub, shf fsrc */
	F_SUB (fsrcfrac, facfrac, facfrac);		/* sub fsrc from fac */
	if ((facfrac.h | facfrac.l) == 0)  {     	/* result zero? */
	    *facp = zero_fac;				/* no overflow */
	    return 0;  }
	if (ediff <= 1) {				/* big normalize? */
	    if ((facfrac.h & (0x00FFFFFF << FP_GUARD)) == 0) {
		F_LSH_K (facfrac, 24, facfrac);
		facexp = facexp - 24;  }
	    if ((facfrac.h & (0x00FFF000 << FP_GUARD)) == 0) {
		F_LSH_K (facfrac, 12, facfrac);
		facexp = facexp - 12;  }
	    if ((facfrac.h & (0x00FC0000 << FP_GUARD)) == 0) {
		F_LSH_K (facfrac, 6, facfrac);
		facexp = facexp - 6;  }  }
	while (GET_BIT (facfrac.h, FP_V_HB + FP_GUARD) == 0) {
	    F_LSH_1 (facfrac);
	    facexp = facexp - 1;  }  }
else {	if (ediff) { F_RSH_V (fsrcfrac, ediff, fsrcfrac);  } /* add, shf fsrc */
	F_ADD (fsrcfrac, facfrac, facfrac);		/* add fsrc to fac */
	if (GET_BIT (facfrac.h, FP_V_HB + FP_GUARD + 1)) {
	    F_RSH_1 (facfrac);				/* carry out, shift */
	    facexp = facexp + 1;  }  }
return round_and_pack (facp, facexp, &facfrac, 1);
}

/* Floating point multiply

   Inputs:
	facp	=	pointer to src1 (output)
	fsrcp	=	pointer to src2
   Outputs:
	ovflo	=	overflow indicator
*/

int32 mulfp11 (fpac_t *facp, fpac_t *fsrcp)
{
int32 facexp, fsrcexp;
fpac_t facfrac, fsrcfrac;

facexp = GET_EXP (facp->h);				/* get exponents */
fsrcexp = GET_EXP (fsrcp->h);
if ((facexp == 0) || (fsrcexp == 0)) {			/* test for zero */
	*facp = zero_fac;
	return 0;  }
F_GET_FRAC_P (facp, facfrac);				/* get fractions */
F_GET_FRAC_P (fsrcp, fsrcfrac);
facexp = facexp + fsrcexp - FP_BIAS;			/* calculate exp */
facp->h = facp->h  ^ fsrcp->h;				/* calculate sign */
frac_mulfp11 (&facfrac, &fsrcfrac);			/* multiply fracs */

/* Multiplying two numbers in the range [.5,1) produces a result in the
   range [.25,1).  Therefore, at most one bit of normalization is required
   to bring the result back to the range [.5,1).
*/

if (GET_BIT (facfrac.h, FP_V_HB + FP_GUARD) == 0) {
	F_LSH_1 (facfrac);
	facexp = facexp - 1;  }
return round_and_pack (facp, facexp, &facfrac, 1);
}

/* Floating point mod

   Inputs:
	facp	=	pointer to src1 (integer result)
	fsrcp	=	pointer to src2
	fracp	=	pointer to fractional result
   Outputs:
	ovflo	=	overflow indicator

   See notes on multiply for initial operation
*/

int32 modfp11 (fpac_t *facp, fpac_t *fsrcp, fpac_t *fracp)
{
int32 facexp, fsrcexp;
fpac_t facfrac, fsrcfrac, fmask;

facexp = GET_EXP (facp->h);				/* get exponents */
fsrcexp = GET_EXP (fsrcp->h);
if ((facexp == 0) || (fsrcexp == 0)) {			/* test for zero */
	*fracp = zero_fac;
	*facp = zero_fac;
	return 0;  }
F_GET_FRAC_P (facp, facfrac);				/* get fractions */
F_GET_FRAC_P (fsrcp, fsrcfrac);
facexp = facexp + fsrcexp - FP_BIAS;			/* calculate exp */
fracp->h = facp->h = facp->h ^ fsrcp->h;		/* calculate sign */
frac_mulfp11 (&facfrac, &fsrcfrac);			/* multiply fracs */

/* Multiplying two numbers in the range [.5,1) produces a result in the
   range [.25,1).  Therefore, at most one bit of normalization is required
   to bring the result back to the range [.5,1).
*/

if (GET_BIT (facfrac.h, FP_V_HB + FP_GUARD) == 0) {
	F_LSH_1 (facfrac);
	facexp = facexp - 1;  }

/* There are three major cases of MODf:

   1. Exp <= FP_BIAS (all fraction).  Return 0 as integer, product as
      fraction.  Underflow can occur.
   2. Exp > FP_BIAS + #fraction bits (all integer).  Return product as
      integer, 0 as fraction.  Overflow can occur.
   3. FP_BIAS < exp <= FP_BIAS + #fraction bits.  Separate integer and
      fraction and return both.  Neither overflow nor underflow can occur.
*/

	if (facexp <= FP_BIAS) {			/* case 1 */
	    *facp = zero_fac;
	    return round_and_pack (fracp, facexp, &facfrac, 1);  }
	if (facexp > ((FPS & FPS_D)? FP_BIAS + 56: FP_BIAS + 24)) {
	    *fracp = zero_fac;				/* case 2 */
	    return round_and_pack (facp, facexp, &facfrac, 0);  }
	F_RSH_V (fmask_fac, facexp - FP_BIAS, fmask);	/* shift mask */
	fsrcfrac.l = facfrac.l & fmask.l;		/* extract fraction */
	fsrcfrac.h = facfrac.h & fmask.h;
	if ((fsrcfrac.h | fsrcfrac.l) == 0) *fracp = zero_fac;
	else {
	    F_LSH_V (fsrcfrac, facexp - FP_BIAS, fsrcfrac);
	    fsrcexp = FP_BIAS;
	    if ((fsrcfrac.h & (0x00FFFFFF << FP_GUARD)) == 0) {
		F_LSH_K (fsrcfrac, 24, fsrcfrac);
		fsrcexp = fsrcexp - 24;  }
	    if ((fsrcfrac.h & (0x00FFF000 << FP_GUARD)) == 0) {
		F_LSH_K (fsrcfrac, 12, fsrcfrac);
		fsrcexp = fsrcexp - 12;  }
	    if ((fsrcfrac.h & (0x00FC0000 << FP_GUARD)) == 0) {
		F_LSH_K (fsrcfrac, 6, fsrcfrac);
		fsrcexp = fsrcexp - 6;  }
	    while (GET_BIT (fsrcfrac.h, FP_V_HB + FP_GUARD) == 0) {
		F_LSH_1 (fsrcfrac);
		fsrcexp = fsrcexp - 1;  }
	    round_and_pack (fracp, fsrcexp, &fsrcfrac, 1);  }
	facfrac.l = facfrac.l & ~fmask.l;
	facfrac.h = facfrac.h & ~fmask.h;
	return round_and_pack (facp, facexp, &facfrac, 0);
}

/* Fraction multiply

   Inputs:
	f1p	=	pointer to multiplier (output)
	f2p	=	pointer to multiplicand fraction

   Note: the inputs are unguarded; the output is guarded.

   This routine performs a classic shift-and-add multiply.  The low
   order bit of the multiplier is tested; if 1, the multiplicand is
   added into the high part of the double precision result.  The
   result and the multiplier are both shifted right 1.

   For the 24b x 24b case, this routine develops 48b of result.
   For the 56b x 56b case, this routine only develops the top 64b
   of the the result.  Because the inputs are normalized fractions,
   the interesting part of the result is the high 56+guard bits.
   Everything shifted off to the right, beyond 64b, plays no part
   in rounding or the result.

   There are many possible optimizations in this routine: scanning
   for groups of zeroes, particularly in the 56b x 56b case; using
   "extended multiply" capability if available in the hardware.
*/

void frac_mulfp11 (fpac_t *f1p, fpac_t *f2p)
{
fpac_t result, mpy, mpc;
int32 i;

result = zero_fac;					/* clear result */
mpy = *f1p;						/* get operands */
mpc = *f2p;
F_LSH_GUARD (mpc);					/* guard multipicand */
if ((mpy.l | mpc.l) == 0) {				/* 24b x 24b? */
	for (i = 0; i < 24; i++) {
	    if (mpy.h & 1) result.h = result.h + mpc.h;
	    F_RSH_1 (result);
	    mpy.h = mpy.h >> 1;  }  }
else {	if (mpy.l != 0) {				/* 24b x 56b? */
	    for (i = 0; i < 32; i++) {
		if (mpy.l & 1) { F_ADD (mpc, result, result);  }
		F_RSH_1 (result);
		mpy.l = mpy.l >> 1;  }  }
	for (i = 0; i < 24; i++) {
	    if (mpy.h & 1) { F_ADD (mpc, result, result);  }
	    F_RSH_1 (result);
	    mpy.h = mpy.h >> 1;  }  }
*f1p = result;
return;
}

/* Floating point divide

   Inputs:
	facp	=	pointer to dividend (output)
	fsrcp	=	pointer to divisor
   Outputs:
	ovflo	=	overflow indicator

   Source operand must be checked for zero by caller!
*/

int32 divfp11 (fpac_t *facp, fpac_t *fsrcp)
{
int32 facexp, fsrcexp, i, count, qd;
fpac_t facfrac, fsrcfrac, quo;

fsrcexp = GET_EXP (fsrcp->h);				/* get divisor exp */
facexp = GET_EXP (facp->h);				/* get dividend exp */
if (facexp == 0) {					/* test for zero */
	*facp = zero_fac;				/* result zero */
	return 0;  }
F_GET_FRAC_P (facp, facfrac);				/* get fractions */
F_GET_FRAC_P (fsrcp, fsrcfrac);
F_LSH_GUARD (facfrac);					/* guard fractions */
F_LSH_GUARD (fsrcfrac);
facexp = facexp - fsrcexp + FP_BIAS + 1;		/* calculate exp */
facp->h = facp->h ^ fsrcp->h;				/* calculate sign */
qd = FPS & FPS_D;
count = FP_V_HB + FP_GUARD + (qd? 33: 1);		/* count = 56b/24b */

quo = zero_fac;
for (i = count; (i > 0) && ((facfrac.h | facfrac.l) != 0); i--) {
	F_LSH_1 (quo);					/* shift quotient */
	if (!F_LT (facfrac, fsrcfrac)) {		/* divd >= divr? */
	    F_SUB (fsrcfrac, facfrac, facfrac);		/* divd - divr */
	    if (qd) quo.l = quo.l | 1;			/* double or single? */
	    else quo.h = quo.h | 1;  }
	F_LSH_1 (facfrac);  }				/* shift divd */
if (i > 0) { F_LSH_V (quo, i, quo);  }			/* early exit? */

/* Dividing two numbers in the range [.5,1) produces a result in the
   range [.5,2).  Therefore, at most one bit of normalization is required
   to bring the result back to the range [.5,1).  The choice of counts
   and quotient bit positions makes this work correctly.
*/

if (GET_BIT (quo.h, FP_V_HB + FP_GUARD) == 0) {
	F_LSH_1 (quo);
	facexp = facexp - 1;  }
return round_and_pack (facp, facexp, &quo, 1);
}

/* Update floating condition codes
   Note that FC is only set by STCfi via the integer condition codes

   Inputs:
	oldst	=	current status
	result	=	high result
	newV	=	new V
   Outputs:
	newst	=	new status
*/

int32 setfcc (int32 oldst, int32 result, int32 newV)
{
oldst = (oldst & ~FPS_CC) | newV;
if (GET_SIGN (result)) oldst = oldst | FPS_N;
if (GET_EXP (result) == 0) oldst = oldst | FPS_Z;
return oldst;
}

/* Round (in place) floating point number to f_floating

   Inputs:
	fptr	=	pointer to floating number
   Outputs:
	ovflow	=	overflow
*/

int32 roundfp11 (fpac_t *fptr)
{
fpac_t outf;

outf = *fptr;						/* get argument */
F_ADD (fround_fac, outf, outf);				/* round */
if (GET_SIGN (outf.h ^ fptr->h)) {			/* flipped sign? */
	outf.h = (outf.h ^ FP_SIGN) & 0xFFFFFFFF;	/* restore sign */
	if (fpnotrap (FEC_OVFLO)) *fptr = zero_fac; 	/* if no int, clear */
	else *fptr = outf;				/* return rounded */
	return FPS_V;  }				/* overflow */
else {	*fptr = outf;					/* round was ok */
	return 0;  }					/* no overflow */
}

/* Round result of calculation, test overflow, pack

   Input:
	facp	=	pointer to result, sign in place
	exp	=	result exponent, right justified
	fracp	=	pointer to result fraction, right justified with
			guard bits
	r	=	round (1) or truncate (0)
   Outputs:
	ovflo	=	overflow indicator
*/

int32 round_and_pack (fpac_t *facp, int32 exp, fpac_t *fracp, int r)
{
fpac_t frac;

frac = *fracp;						/* get fraction */
if (r && ((FPS & FPS_T) == 0)) { 
	if (FPS & FPS_D) { F_ADD (dround_guard_fac, frac, frac);  }
	else { F_ADD (fround_guard_fac, frac, frac);  }
	if (GET_BIT (frac.h, FP_V_HB + FP_GUARD + 1)) {
	    F_RSH_1 (frac);
	    exp = exp + 1;  }  }
F_RSH_GUARD (frac);
facp->l = frac.l & FP_FRACL;
facp->h = (facp->h & FP_SIGN) | ((exp & FP_M_EXP) << FP_V_EXP) |
	(frac.h & FP_FRACH);
if (exp > 0377) {
	if (fpnotrap (FEC_OVFLO)) *facp = zero_fac;
	return FPS_V;  }
if ((exp <= 0) && (fpnotrap (FEC_UNFLO))) *facp = zero_fac;
return 0;
}

/* Process floating point exception

   Inputs:
	code	=	exception code
   Outputs:
	int	=	FALSE if interrupt enabled, TRUE if disabled
*/

int32 fpnotrap (int32 code)
{
static const int32 test_code[] = { 0, 0, 0, FPS_IC, FPS_IV, FPS_IU, FPS_IUV };

if ((code >= FEC_ICVT) && (code <= FEC_UNDFV) &&
    ((FPS & test_code[code >> 1]) == 0)) return TRUE;
FPS = FPS | FPS_ER;
FEC = code;
FEA = (backup_PC - 2) & 0177777;
if ((FPS & FPS_ID) == 0) setTRAP (TRAP_FPE);
return FALSE;
}