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https://github.com/Ryujinx/Ryujinx.git
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103 lines
2.8 KiB
C#
103 lines
2.8 KiB
C#
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using System;
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namespace ChocolArm64.Instruction
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{
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static class ASoftFloat
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{
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static ASoftFloat()
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{
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InvSqrtEstimateTable = BuildInvSqrtEstimateTable();
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}
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private static readonly byte[] InvSqrtEstimateTable;
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private static byte[] BuildInvSqrtEstimateTable()
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{
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byte[] Table = new byte[512];
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for (ulong index = 128; index < 512; index++)
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{
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ulong a = index;
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if (a < 256)
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{
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a = (a << 1) + 1;
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}
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else
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{
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a = (a | 1) << 1;
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}
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ulong b = 256;
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while (a * (b + 1) * (b + 1) < (1ul << 28))
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{
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b++;
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}
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b = (b + 1) >> 1;
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Table[index] = (byte)(b & 0xFF);
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}
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return Table;
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}
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public static float InvSqrtEstimate(float x)
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{
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return (float)InvSqrtEstimate((double)x);
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}
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public static double InvSqrtEstimate(double x)
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{
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ulong x_bits = (ulong)BitConverter.DoubleToInt64Bits(x);
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ulong x_sign = x_bits & 0x8000000000000000;
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long x_exp = (long)((x_bits >> 52) & 0x7FF);
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ulong scaled = x_bits & ((1ul << 52) - 1);
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if (x_exp == 0x7ff)
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{
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if (scaled == 0)
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{
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// Infinity -> Zero
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return BitConverter.Int64BitsToDouble((long)x_sign);
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}
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// NaN
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return BitConverter.Int64BitsToDouble((long)(x_bits | 0x0008000000000000));
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}
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if (x_exp == 0)
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{
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if (scaled == 0)
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{
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// Zero -> Infinity
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return BitConverter.Int64BitsToDouble((long)(x_sign | 0x7ff0000000000000));
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}
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// Denormal
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while ((scaled & (1 << 51)) == 0)
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{
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scaled <<= 1;
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x_exp--;
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}
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scaled <<= 1;
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}
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if (((ulong)x_exp & 1) == 1)
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{
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scaled >>= 45;
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scaled &= 0xFF;
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scaled |= 0x80;
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}
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else
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{
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scaled >>= 44;
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scaled &= 0xFF;
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scaled |= 0x100;
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}
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ulong result_exp = ((ulong)(3068 - x_exp) / 2) & 0x7FF;
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ulong estimate = (ulong)InvSqrtEstimateTable[scaled];
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ulong fraction = estimate << 44;
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ulong result = x_sign | (result_exp << 52) | fraction;
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return BitConverter.Int64BitsToDouble((long)result);
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}
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}
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}
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