/* * 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 1.2 1994/04/29 21:30:15 gclarkii 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 }