KVM: emulator: emulate AAM
[linux-3.10.git] / arch / x86 / math-emu / poly_2xm1.c
1 /*---------------------------------------------------------------------------+
2  |  poly_2xm1.c                                                              |
3  |                                                                           |
4  | Function to compute 2^x-1 by a polynomial approximation.                  |
5  |                                                                           |
6  | Copyright (C) 1992,1993,1994,1997                                         |
7  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
8  |                  E-mail   billm@suburbia.net                              |
9  |                                                                           |
10  |                                                                           |
11  +---------------------------------------------------------------------------*/
12
13 #include "exception.h"
14 #include "reg_constant.h"
15 #include "fpu_emu.h"
16 #include "fpu_system.h"
17 #include "control_w.h"
18 #include "poly.h"
19
20 #define HIPOWER 11
21 static const unsigned long long lterms[HIPOWER] = {
22         0x0000000000000000LL,   /* This term done separately as 12 bytes */
23         0xf5fdeffc162c7543LL,
24         0x1c6b08d704a0bfa6LL,
25         0x0276556df749cc21LL,
26         0x002bb0ffcf14f6b8LL,
27         0x0002861225ef751cLL,
28         0x00001ffcbfcd5422LL,
29         0x00000162c005d5f1LL,
30         0x0000000da96ccb1bLL,
31         0x0000000078d1b897LL,
32         0x000000000422b029LL
33 };
34
35 static const Xsig hiterm = MK_XSIG(0xb17217f7, 0xd1cf79ab, 0xc8a39194);
36
37 /* Four slices: 0.0 : 0.25 : 0.50 : 0.75 : 1.0,
38    These numbers are 2^(1/4), 2^(1/2), and 2^(3/4)
39  */
40 static const Xsig shiftterm0 = MK_XSIG(0, 0, 0);
41 static const Xsig shiftterm1 = MK_XSIG(0x9837f051, 0x8db8a96f, 0x46ad2318);
42 static const Xsig shiftterm2 = MK_XSIG(0xb504f333, 0xf9de6484, 0x597d89b3);
43 static const Xsig shiftterm3 = MK_XSIG(0xd744fcca, 0xd69d6af4, 0x39a68bb9);
44
45 static const Xsig *shiftterm[] = { &shiftterm0, &shiftterm1,
46         &shiftterm2, &shiftterm3
47 };
48
49 /*--- poly_2xm1() -----------------------------------------------------------+
50  | Requires st(0) which is TAG_Valid and < 1.                                |
51  +---------------------------------------------------------------------------*/
52 int poly_2xm1(u_char sign, FPU_REG *arg, FPU_REG *result)
53 {
54         long int exponent, shift;
55         unsigned long long Xll;
56         Xsig accumulator, Denom, argSignif;
57         u_char tag;
58
59         exponent = exponent16(arg);
60
61 #ifdef PARANOID
62         if (exponent >= 0) {    /* Don't want a |number| >= 1.0 */
63                 /* Number negative, too large, or not Valid. */
64                 EXCEPTION(EX_INTERNAL | 0x127);
65                 return 1;
66         }
67 #endif /* PARANOID */
68
69         argSignif.lsw = 0;
70         XSIG_LL(argSignif) = Xll = significand(arg);
71
72         if (exponent == -1) {
73                 shift = (argSignif.msw & 0x40000000) ? 3 : 2;
74                 /* subtract 0.5 or 0.75 */
75                 exponent -= 2;
76                 XSIG_LL(argSignif) <<= 2;
77                 Xll <<= 2;
78         } else if (exponent == -2) {
79                 shift = 1;
80                 /* subtract 0.25 */
81                 exponent--;
82                 XSIG_LL(argSignif) <<= 1;
83                 Xll <<= 1;
84         } else
85                 shift = 0;
86
87         if (exponent < -2) {
88                 /* Shift the argument right by the required places. */
89                 if (FPU_shrx(&Xll, -2 - exponent) >= 0x80000000U)
90                         Xll++;  /* round up */
91         }
92
93         accumulator.lsw = accumulator.midw = accumulator.msw = 0;
94         polynomial_Xsig(&accumulator, &Xll, lterms, HIPOWER - 1);
95         mul_Xsig_Xsig(&accumulator, &argSignif);
96         shr_Xsig(&accumulator, 3);
97
98         mul_Xsig_Xsig(&argSignif, &hiterm);     /* The leading term */
99         add_two_Xsig(&accumulator, &argSignif, &exponent);
100
101         if (shift) {
102                 /* The argument is large, use the identity:
103                    f(x+a) = f(a) * (f(x) + 1) - 1;
104                  */
105                 shr_Xsig(&accumulator, -exponent);
106                 accumulator.msw |= 0x80000000;  /* add 1.0 */
107                 mul_Xsig_Xsig(&accumulator, shiftterm[shift]);
108                 accumulator.msw &= 0x3fffffff;  /* subtract 1.0 */
109                 exponent = 1;
110         }
111
112         if (sign != SIGN_POS) {
113                 /* The argument is negative, use the identity:
114                    f(-x) = -f(x) / (1 + f(x))
115                  */
116                 Denom.lsw = accumulator.lsw;
117                 XSIG_LL(Denom) = XSIG_LL(accumulator);
118                 if (exponent < 0)
119                         shr_Xsig(&Denom, -exponent);
120                 else if (exponent > 0) {
121                         /* exponent must be 1 here */
122                         XSIG_LL(Denom) <<= 1;
123                         if (Denom.lsw & 0x80000000)
124                                 XSIG_LL(Denom) |= 1;
125                         (Denom.lsw) <<= 1;
126                 }
127                 Denom.msw |= 0x80000000;        /* add 1.0 */
128                 div_Xsig(&accumulator, &Denom, &accumulator);
129         }
130
131         /* Convert to 64 bit signed-compatible */
132         exponent += round_Xsig(&accumulator);
133
134         result = &st(0);
135         significand(result) = XSIG_LL(accumulator);
136         setexponent16(result, exponent);
137
138         tag = FPU_round(result, 1, 0, FULL_PRECISION, sign);
139
140         setsign(result, sign);
141         FPU_settag0(tag);
142
143         return 0;
144
145 }