blob: 7bee69baea184c95f7709049dab611878a96e306 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
|
using System;
namespace ChocolArm64.Instruction
{
static class ASoftFloat
{
static ASoftFloat()
{
InvSqrtEstimateTable = BuildInvSqrtEstimateTable();
}
private static readonly byte[] InvSqrtEstimateTable;
private static byte[] BuildInvSqrtEstimateTable()
{
byte[] Table = new byte[512];
for (ulong index = 128; index < 512; index++)
{
ulong a = index;
if (a < 256)
{
a = (a << 1) + 1;
}
else
{
a = (a | 1) << 1;
}
ulong b = 256;
while (a * (b + 1) * (b + 1) < (1ul << 28))
{
b++;
}
b = (b + 1) >> 1;
Table[index] = (byte)(b & 0xFF);
}
return Table;
}
public static float InvSqrtEstimate(float x)
{
return (float)InvSqrtEstimate((double)x);
}
public static double InvSqrtEstimate(double x)
{
ulong x_bits = (ulong)BitConverter.DoubleToInt64Bits(x);
ulong x_sign = x_bits & 0x8000000000000000;
long x_exp = (long)((x_bits >> 52) & 0x7FF);
ulong scaled = x_bits & ((1ul << 52) - 1);
if (x_exp == 0x7ff)
{
if (scaled == 0)
{
// Infinity -> Zero
return BitConverter.Int64BitsToDouble((long)x_sign);
}
// NaN
return BitConverter.Int64BitsToDouble((long)(x_bits | 0x0008000000000000));
}
if (x_exp == 0)
{
if (scaled == 0)
{
// Zero -> Infinity
return BitConverter.Int64BitsToDouble((long)(x_sign | 0x7ff0000000000000));
}
// Denormal
while ((scaled & (1 << 51)) == 0)
{
scaled <<= 1;
x_exp--;
}
scaled <<= 1;
}
if (((ulong)x_exp & 1) == 1)
{
scaled >>= 45;
scaled &= 0xFF;
scaled |= 0x80;
}
else
{
scaled >>= 44;
scaled &= 0xFF;
scaled |= 0x100;
}
ulong result_exp = ((ulong)(3068 - x_exp) / 2) & 0x7FF;
ulong estimate = (ulong)InvSqrtEstimateTable[scaled];
ulong fraction = estimate << 44;
ulong result = x_sign | (result_exp << 52) | fraction;
return BitConverter.Int64BitsToDouble((long)result);
}
}
}
|
