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+/*
+ * reg_add_sub.c
+ *
+ * Functions to add or subtract two registers and put the result in a third.
+ *
+ * Copyright (C) 1992,1993,1994
+ * W. Metzenthen, 22 Parker St, Ormond, Vic 3163,
+ * Australia. E-mail billm@vaxc.cc.monash.edu.au
+ * All rights reserved.
+ *
+ * This copyright notice covers the redistribution and use of the
+ * FPU emulator developed by W. Metzenthen. It covers only its use
+ * in the 386BSD, FreeBSD and NetBSD operating systems. Any other
+ * use is not permitted under this copyright.
+ *
+ * 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 include information specifying
+ * that source code for the emulator is freely available and include
+ * either:
+ * a) an offer to provide the source code for a nominal distribution
+ * fee, or
+ * b) list at least two alternative methods whereby the source
+ * can be obtained, e.g. a publically accessible bulletin board
+ * and an anonymous ftp site from which the software can be
+ * downloaded.
+ * 3. All advertising materials specifically mentioning features or use of
+ * this emulator must acknowledge that it was developed by W. Metzenthen.
+ * 4. The name of W. Metzenthen may not be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED ``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
+ * W. METZENTHEN 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.
+ *
+ *
+ * The purpose of this copyright, based upon the Berkeley copyright, is to
+ * ensure that the covered software remains freely available to everyone.
+ *
+ * The software (with necessary differences) is also available, but under
+ * the terms of the GNU copyleft, for the Linux operating system and for
+ * the djgpp ms-dos extender.
+ *
+ * W. Metzenthen June 1994.
+ *
+ *
+ * $Id: reg_add_sub.c,v 1.3 1994/06/10 07:44:44 rich Exp $
+ *
+ */
+
+/*---------------------------------------------------------------------------+
+ | For each function, the destination may be any FPU_REG, including one of |
+ | the source FPU_REGs. |
+ +---------------------------------------------------------------------------*/
+
+#include "exception.h"
+#include "reg_constant.h"
+#include "fpu_emu.h"
+#include "control_w.h"
+#include "fpu_system.h"
+
+
+void
+reg_add(FPU_REG * a, FPU_REG * b, FPU_REG * dest, int control_w)
+{
+ int diff;
+
+ if (!(a->tag | b->tag)) {
+ /* Both registers are valid */
+ if (!(a->sign ^ b->sign)) {
+ /* signs are the same */
+ reg_u_add(a, b, dest, control_w);
+ dest->sign = a->sign;
+ return;
+ }
+ /* The signs are different, so do a subtraction */
+ diff = a->exp - b->exp;
+ if (!diff) {
+ diff = a->sigh - b->sigh; /* Works only if ms bits
+ * are identical */
+ if (!diff) {
+ diff = a->sigl > b->sigl;
+ if (!diff)
+ diff = -(a->sigl < b->sigl);
+ }
+ }
+ if (diff > 0) {
+ reg_u_sub(a, b, dest, control_w);
+ dest->sign = a->sign;
+ } else
+ if (diff == 0) {
+ reg_move(&CONST_Z, dest);
+ /* sign depends upon rounding mode */
+ dest->sign = ((control_w & CW_RC) != RC_DOWN)
+ ? SIGN_POS : SIGN_NEG;
+ } else {
+ reg_u_sub(b, a, dest, control_w);
+ dest->sign = b->sign;
+ }
+ return;
+ } else {
+ if ((a->tag == TW_NaN) || (b->tag == TW_NaN)) {
+ real_2op_NaN(a, b, dest);
+ return;
+ } else
+ if (a->tag == TW_Zero) {
+ if (b->tag == TW_Zero) {
+ char different_signs = a->sign ^ b->sign;
+ /* Both are zero, result will be zero. */
+ reg_move(a, dest);
+ if (different_signs) {
+ /* Signs are different. */
+ /* Sign of answer depends upon
+ * rounding mode. */
+ dest->sign = ((control_w & CW_RC) != RC_DOWN)
+ ? SIGN_POS : SIGN_NEG;
+ }
+ } else {
+#ifdef DENORM_OPERAND
+ if ((b->tag == TW_Valid) && (b->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(b, dest);
+ }
+ return;
+ } else
+ if (b->tag == TW_Zero) {
+#ifdef DENORM_OPERAND
+ if ((a->tag == TW_Valid) && (a->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(a, dest);
+ return;
+ } else
+ if (a->tag == TW_Infinity) {
+ if (b->tag != TW_Infinity) {
+#ifdef DENORM_OPERAND
+ if ((b->tag == TW_Valid) && (b->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(a, dest);
+ return;
+ }
+ if (a->sign == b->sign) {
+ /* They are both + or
+ * - infinity */
+ reg_move(a, dest);
+ return;
+ }
+ arith_invalid(dest); /* Infinity-Infinity is
+ * undefined. */
+ return;
+ } else
+ if (b->tag == TW_Infinity) {
+#ifdef DENORM_OPERAND
+ if ((a->tag == TW_Valid) && (a->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(b, dest);
+ return;
+ }
+ }
+#ifdef PARANOID
+ EXCEPTION(EX_INTERNAL | 0x101);
+#endif
+}
+
+
+/* Subtract b from a. (a-b) -> dest */
+void
+reg_sub(FPU_REG * a, FPU_REG * b, FPU_REG * dest, int control_w)
+{
+ int diff;
+
+ if (!(a->tag | b->tag)) {
+ /* Both registers are valid */
+ diff = a->exp - b->exp;
+ if (!diff) {
+ diff = a->sigh - b->sigh; /* Works only if ms bits
+ * are identical */
+ if (!diff) {
+ diff = a->sigl > b->sigl;
+ if (!diff)
+ diff = -(a->sigl < b->sigl);
+ }
+ }
+ switch (a->sign * 2 + b->sign) {
+ case 0: /* P - P */
+ case 3: /* N - N */
+ if (diff > 0) {
+ reg_u_sub(a, b, dest, control_w);
+ dest->sign = a->sign;
+ } else
+ if (diff == 0) {
+#ifdef DENORM_OPERAND
+ if ((b->tag == TW_Valid) && (b->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(&CONST_Z, dest);
+ /* sign depends upon rounding mode */
+ dest->sign = ((control_w & CW_RC) != RC_DOWN)
+ ? SIGN_POS : SIGN_NEG;
+ } else {
+ reg_u_sub(b, a, dest, control_w);
+ dest->sign = a->sign ^ SIGN_POS ^ SIGN_NEG;
+ }
+ return;
+ case 1: /* P - N */
+ reg_u_add(a, b, dest, control_w);
+ dest->sign = SIGN_POS;
+ return;
+ case 2: /* N - P */
+ reg_u_add(a, b, dest, control_w);
+ dest->sign = SIGN_NEG;
+ return;
+ }
+ } else {
+ if ((a->tag == TW_NaN) || (b->tag == TW_NaN)) {
+ real_2op_NaN(a, b, dest);
+ return;
+ } else
+ if (b->tag == TW_Zero) {
+ if (a->tag == TW_Zero) {
+ char same_signs = !(a->sign ^ b->sign);
+ /* Both are zero, result will be zero. */
+ reg_move(a, dest); /* Answer for different
+ * signs. */
+ if (same_signs) {
+ /* Sign depends upon rounding
+ * mode */
+ dest->sign = ((control_w & CW_RC) != RC_DOWN)
+ ? SIGN_POS : SIGN_NEG;
+ }
+ } else {
+#ifdef DENORM_OPERAND
+ if ((a->tag == TW_Valid) && (a->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(a, dest);
+ }
+ return;
+ } else
+ if (a->tag == TW_Zero) {
+#ifdef DENORM_OPERAND
+ if ((b->tag == TW_Valid) && (b->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(b, dest);
+ dest->sign ^= SIGN_POS ^ SIGN_NEG;
+ return;
+ } else
+ if (a->tag == TW_Infinity) {
+ if (b->tag != TW_Infinity) {
+#ifdef DENORM_OPERAND
+ if ((b->tag == TW_Valid) && (b->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(a, dest);
+ return;
+ }
+ /* Both args are Infinity */
+ if (a->sign == b->sign) {
+ arith_invalid(dest); /* Infinity-Infinity is
+ * undefined. */
+ return;
+ }
+ reg_move(a, dest);
+ return;
+ } else
+ if (b->tag == TW_Infinity) {
+#ifdef DENORM_OPERAND
+ if ((a->tag == TW_Valid) && (a->exp <= EXP_UNDER) &&
+ denormal_operand())
+ return;
+#endif /* DENORM_OPERAND */
+ reg_move(b, dest);
+ dest->sign ^= SIGN_POS ^ SIGN_NEG;
+ return;
+ }
+ }
+#ifdef PARANOID
+ EXCEPTION(EX_INTERNAL | 0x110);
+#endif
+}
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