3 /*-
4  * SPDX-License-Identifier: BSD-3-Clause
10  * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
44  * Perform an FPU add (return x + y).
46  * To subtract, negate y and call add.
61 	struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r;  in fpu_add()  local
70 	 *  - y = NaN.  Implied: if only one is a signalling NaN, y is.  in fpu_add()
71 	 *	The result is y.  in fpu_add()
72 	 *  - y = Inf.  Implied: x != NaN (is 0, number, or Inf: the NaN  in fpu_add()
74 	 *	If x = -y, the result is NaN.  Otherwise the result  in fpu_add()
75 	 *	is y (an Inf of whichever sign).  in fpu_add()
76 	 *  - y is 0.  Implied: x = 0.  in fpu_add()
77 	 *	If x and y differ in sign (one positive, one negative),  in fpu_add()
78 	 *	the result is +0 except when rounding to -Inf.  If same:  in fpu_add()
79 	 *	+0 + +0 = +0; -0 + -0 = -0.  in fpu_add()
80 	 *  - x is 0.  Implied: y != 0.  in fpu_add()
81 	 *	Result is y.  in fpu_add()
82 	 *  - other.  Implied: both x and y are numbers.  in fpu_add()
87 	DUMPFPN(FPE_REG, y);  in fpu_add()
89 	ORDER(x, y);  in fpu_add()
90 	if (ISNAN(y)) {  in fpu_add()
91 		fe->fe_cx |= FPSCR_VXSNAN;  in fpu_add()
92 		DUMPFPN(FPE_REG, y);  in fpu_add()
93 		return (y);  in fpu_add()
95 	if (ISINF(y)) {  in fpu_add()
96 		if (ISINF(x) && x->fp_sign != y->fp_sign) {  in fpu_add()
97 			fe->fe_cx |= FPSCR_VXISI;  in fpu_add()
100 		DUMPFPN(FPE_REG, y);  in fpu_add()
101 		return (y);  in fpu_add()
103 	rd = ((fe->fe_fpscr) & FPSCR_RN);  in fpu_add()
104 	if (ISZERO(y)) {  in fpu_add()
105 		if (rd != FP_RM)	/* only -0 + -0 gives -0 */  in fpu_add()
106 			y->fp_sign &= x->fp_sign;  in fpu_add()
107 		else			/* any -0 operand gives -0 */  in fpu_add()
108 			y->fp_sign |= x->fp_sign;  in fpu_add()
109 		DUMPFPN(FPE_REG, y);  in fpu_add()
110 		return (y);  in fpu_add()
113 		DUMPFPN(FPE_REG, y);  in fpu_add()
114 		return (y);  in fpu_add()
121 	 * of x and y here.  in fpu_add()
123 	r = &fe->fe_f3;  in fpu_add()
124 	r->fp_class = FPC_NUM;  in fpu_add()
125 	if (x->fp_exp == y->fp_exp) {  in fpu_add()
126 		r->fp_exp = x->fp_exp;  in fpu_add()
127 		r->fp_sticky = 0;  in fpu_add()
129 		if (x->fp_exp < y->fp_exp) {  in fpu_add()
132 			 * This also guarantees that x->fp_sticky = 0.  in fpu_add()
134 			SWAP(x, y);  in fpu_add()
136 		/* now x->fp_exp > y->fp_exp */  in fpu_add()
137 		r->fp_exp = x->fp_exp;  in fpu_add()
138 		r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp);  in fpu_add()
140 	r->fp_sign = x->fp_sign;  in fpu_add()
141 	if (x->fp_sign == y->fp_sign) {  in fpu_add()
147 		 * 11.111...0).  If so, a single bit shift-right will fix it  in fpu_add()
150 		/* r->fp_mant = x->fp_mant + y->fp_mant */  in fpu_add()
151 		FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]);  in fpu_add()
152 		FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]);  in fpu_add()
153 		FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]);  in fpu_add()
154 		FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]);  in fpu_add()
155 		if ((r->fp_mant[0] = r0) >= FP_2) {  in fpu_add()
157 			r->fp_exp++;  in fpu_add()
167 		 * y from x, regardless of whether y itself is the negative  in fpu_add()
169 		 * hold, depending on the magnitudes of x and y:  in fpu_add()
170 		 *   case i)   |x| > |y|.  The result is just x - y,  in fpu_add()
172 		 *   case ii)  |x| = |y|.  The result is 0 (maybe -0)  in fpu_add()
174 		 *   case iii) |x| < |y|.  We goofed; the result should  in fpu_add()
175 		 *	be (y - x), with the same sign as y.  in fpu_add()
176 		 * We could compare |x| and |y| here and avoid case iii,  in fpu_add()
180 		 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0.  in fpu_add()
182 		/* r->fp_mant = x->fp_mant - y->fp_mant */  in fpu_add()
183 		FPU_SET_CARRY(y->fp_sticky);  in fpu_add()
184 		FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]);  in fpu_add()
185 		FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]);  in fpu_add()
186 		FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]);  in fpu_add()
187 		FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]);  in fpu_add()
192 				r->fp_class = FPC_ZERO;  in fpu_add()
193 				r->fp_sign = rd == FP_RM;  in fpu_add()
200 			 * x nor y have sticky bits set.  Flip the sign  in fpu_add()
201 			 * (to y's sign) and negate the result to get y - x.  in fpu_add()
204 			if (x->fp_exp != y->fp_exp || r->fp_sticky)  in fpu_add()
207 			r->fp_sign = y->fp_sign;  in fpu_add()
213 		r->fp_mant[3] = r3;  in fpu_add()
214 		r->fp_mant[2] = r2;  in fpu_add()
215 		r->fp_mant[1] = r1;  in fpu_add()
216 		r->fp_mant[0] = r0;  in fpu_add()