1 // SPDX-License-Identifier: GPL-2.0-only
2 /* IEEE754 floating point arithmetic
3  * double precision: common utilities
4  */
5 /*
6  * MIPS floating point support
7  * Copyright (C) 1994-2000 Algorithmics Ltd.
8  */
9 
10 #include "ieee754dp.h"
11 
ieee754dp_tlong(union ieee754dp x)12 s64 ieee754dp_tlong(union ieee754dp x)
13 {
14 	u64 residue;
15 	int round;
16 	int sticky;
17 	int odd;
18 
19 	COMPXDP;
20 
21 	ieee754_clearcx();
22 
23 	EXPLODEXDP;
24 	FLUSHXDP;
25 
26 	switch (xc) {
27 	case IEEE754_CLASS_SNAN:
28 	case IEEE754_CLASS_QNAN:
29 		ieee754_setcx(IEEE754_INVALID_OPERATION);
30 		return ieee754di_indef();
31 
32 	case IEEE754_CLASS_INF:
33 		ieee754_setcx(IEEE754_INVALID_OPERATION);
34 		return ieee754di_overflow(xs);
35 
36 	case IEEE754_CLASS_ZERO:
37 		return 0;
38 
39 	case IEEE754_CLASS_DNORM:
40 	case IEEE754_CLASS_NORM:
41 		break;
42 	}
43 	if (xe >= 63) {
44 		/* look for valid corner case */
45 		if (xe == 63 && xs && xm == DP_HIDDEN_BIT)
46 			return -0x8000000000000000LL;
47 		/* Set invalid. We will only use overflow for floating
48 		   point overflow */
49 		ieee754_setcx(IEEE754_INVALID_OPERATION);
50 		return ieee754di_overflow(xs);
51 	}
52 	/* oh gawd */
53 	if (xe > DP_FBITS) {
54 		xm <<= xe - DP_FBITS;
55 	} else if (xe < DP_FBITS) {
56 		if (xe < -1) {
57 			residue = xm;
58 			round = 0;
59 			sticky = residue != 0;
60 			xm = 0;
61 		} else {
62 			/* Shifting a u64 64 times does not work,
63 			* so we do it in two steps. Be aware that xe
64 			* may be -1 */
65 			residue = xm << (xe + 1);
66 			residue <<= 63 - DP_FBITS;
67 			round = (residue >> 63) != 0;
68 			sticky = (residue << 1) != 0;
69 			xm >>= DP_FBITS - xe;
70 		}
71 		odd = (xm & 0x1) != 0x0;
72 		switch (ieee754_csr.rm) {
73 		case FPU_CSR_RN:
74 			if (round && (sticky || odd))
75 				xm++;
76 			break;
77 		case FPU_CSR_RZ:
78 			break;
79 		case FPU_CSR_RU:	/* toward +Infinity */
80 			if ((round || sticky) && !xs)
81 				xm++;
82 			break;
83 		case FPU_CSR_RD:	/* toward -Infinity */
84 			if ((round || sticky) && xs)
85 				xm++;
86 			break;
87 		}
88 		if ((xm >> 63) != 0) {
89 			/* This can happen after rounding */
90 			ieee754_setcx(IEEE754_INVALID_OPERATION);
91 			return ieee754di_overflow(xs);
92 		}
93 		if (round || sticky)
94 			ieee754_setcx(IEEE754_INEXACT);
95 	}
96 	if (xs)
97 		return -xm;
98 	else
99 		return xm;
100 }
101