Common: Move floating-point utility functions to FloatUtils.h/.cpp

Keeps all of the floating-point utility functions in their own file to
keep them all together. This also provides a place for other
general-purpose floating-point functions to be added in the future,
which will be necessary when improving the flag-setting within the
interpreter.

1 files changed, 216 insertions, 0 deletions

diff --git a/Source/Core/Common/FloatUtils.cpp b/Source/Core/Common/FloatUtils.cpp
new file mode 100644
index 0000000000..4bbb4266d6
--- /dev/null
+++ b/Source/Core/Common/FloatUtils.cpp
@@ -0,0 +1,216 @@
+// Copyright 2018 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include "Common/FloatUtils.h"
+
+#include <cmath>
+
+namespace Common
+{
+u32 ClassifyDouble(double dvalue)
+{
+  // TODO: Optimize the below to be as fast as possible.
+  IntDouble value(dvalue);
+  u64 sign = value.i & DOUBLE_SIGN;
+  u64 exp = value.i & DOUBLE_EXP;
+  if (exp > DOUBLE_ZERO && exp < DOUBLE_EXP)
+  {
+    // Nice normalized number.
+    return sign ? PPC_FPCLASS_NN : PPC_FPCLASS_PN;
+  }
+  else
+  {
+    u64 mantissa = value.i & DOUBLE_FRAC;
+    if (mantissa)
+    {
+      if (exp)
+      {
+        return PPC_FPCLASS_QNAN;
+      }
+      else
+      {
+        // Denormalized number.
+        return sign ? PPC_FPCLASS_ND : PPC_FPCLASS_PD;
+      }
+    }
+    else if (exp)
+    {
+      // Infinite
+      return sign ? PPC_FPCLASS_NINF : PPC_FPCLASS_PINF;
+    }
+    else
+    {
+      // Zero
+      return sign ? PPC_FPCLASS_NZ : PPC_FPCLASS_PZ;
+    }
+  }
+}
+
+u32 ClassifyFloat(float fvalue)
+{
+  // TODO: Optimize the below to be as fast as possible.
+  IntFloat value(fvalue);
+  u32 sign = value.i & FLOAT_SIGN;
+  u32 exp = value.i & FLOAT_EXP;
+  if (exp > FLOAT_ZERO && exp < FLOAT_EXP)
+  {
+    // Nice normalized number.
+    return sign ? PPC_FPCLASS_NN : PPC_FPCLASS_PN;
+  }
+  else
+  {
+    u32 mantissa = value.i & FLOAT_FRAC;
+    if (mantissa)
+    {
+      if (exp)
+      {
+        return PPC_FPCLASS_QNAN;  // Quiet NAN
+      }
+      else
+      {
+        // Denormalized number.
+        return sign ? PPC_FPCLASS_ND : PPC_FPCLASS_PD;
+      }
+    }
+    else if (exp)
+    {
+      // Infinite
+      return sign ? PPC_FPCLASS_NINF : PPC_FPCLASS_PINF;
+    }
+    else
+    {
+      // Zero
+      return sign ? PPC_FPCLASS_NZ : PPC_FPCLASS_PZ;
+    }
+  }
+}
+
+const std::array<BaseAndDec, 32> frsqrte_expected = {{
+    {0x3ffa000, 0x7a4}, {0x3c29000, 0x700}, {0x38aa000, 0x670}, {0x3572000, 0x5f2},
+    {0x3279000, 0x584}, {0x2fb7000, 0x524}, {0x2d26000, 0x4cc}, {0x2ac0000, 0x47e},
+    {0x2881000, 0x43a}, {0x2665000, 0x3fa}, {0x2468000, 0x3c2}, {0x2287000, 0x38e},
+    {0x20c1000, 0x35e}, {0x1f12000, 0x332}, {0x1d79000, 0x30a}, {0x1bf4000, 0x2e6},
+    {0x1a7e800, 0x568}, {0x17cb800, 0x4f3}, {0x1552800, 0x48d}, {0x130c000, 0x435},
+    {0x10f2000, 0x3e7}, {0x0eff000, 0x3a2}, {0x0d2e000, 0x365}, {0x0b7c000, 0x32e},
+    {0x09e5000, 0x2fc}, {0x0867000, 0x2d0}, {0x06ff000, 0x2a8}, {0x05ab800, 0x283},
+    {0x046a000, 0x261}, {0x0339800, 0x243}, {0x0218800, 0x226}, {0x0105800, 0x20b},
+}};
+
+double ApproximateReciprocalSquareRoot(double val)
+{
+  union
+  {
+    double valf;
+    s64 vali;
+  };
+  valf = val;
+  s64 mantissa = vali & ((1LL << 52) - 1);
+  s64 sign = vali & (1ULL << 63);
+  s64 exponent = vali & (0x7FFLL << 52);
+
+  // Special case 0
+  if (mantissa == 0 && exponent == 0)
+    return sign ? -std::numeric_limits<double>::infinity() :
+                  std::numeric_limits<double>::infinity();
+  // Special case NaN-ish numbers
+  if (exponent == (0x7FFLL << 52))
+  {
+    if (mantissa == 0)
+    {
+      if (sign)
+        return std::numeric_limits<double>::quiet_NaN();
+
+      return 0.0;
+    }
+
+    return 0.0 + valf;
+  }
+
+  // Negative numbers return NaN
+  if (sign)
+    return std::numeric_limits<double>::quiet_NaN();
+
+  if (!exponent)
+  {
+    // "Normalize" denormal values
+    do
+    {
+      exponent -= 1LL << 52;
+      mantissa <<= 1;
+    } while (!(mantissa & (1LL << 52)));
+    mantissa &= (1LL << 52) - 1;
+    exponent += 1LL << 52;
+  }
+
+  bool odd_exponent = !(exponent & (1LL << 52));
+  exponent = ((0x3FFLL << 52) - ((exponent - (0x3FELL << 52)) / 2)) & (0x7FFLL << 52);
+
+  int i = (int)(mantissa >> 37);
+  vali = sign | exponent;
+  int index = i / 2048 + (odd_exponent ? 16 : 0);
+  const auto& entry = frsqrte_expected[index];
+  vali |= (s64)(entry.m_base - entry.m_dec * (i % 2048)) << 26;
+  return valf;
+}
+
+const std::array<BaseAndDec, 32> fres_expected = {{
+    {0x7ff800, 0x3e1}, {0x783800, 0x3a7}, {0x70ea00, 0x371}, {0x6a0800, 0x340}, {0x638800, 0x313},
+    {0x5d6200, 0x2ea}, {0x579000, 0x2c4}, {0x520800, 0x2a0}, {0x4cc800, 0x27f}, {0x47ca00, 0x261},
+    {0x430800, 0x245}, {0x3e8000, 0x22a}, {0x3a2c00, 0x212}, {0x360800, 0x1fb}, {0x321400, 0x1e5},
+    {0x2e4a00, 0x1d1}, {0x2aa800, 0x1be}, {0x272c00, 0x1ac}, {0x23d600, 0x19b}, {0x209e00, 0x18b},
+    {0x1d8800, 0x17c}, {0x1a9000, 0x16e}, {0x17ae00, 0x15b}, {0x14f800, 0x15b}, {0x124400, 0x143},
+    {0x0fbe00, 0x143}, {0x0d3800, 0x12d}, {0x0ade00, 0x12d}, {0x088400, 0x11a}, {0x065000, 0x11a},
+    {0x041c00, 0x108}, {0x020c00, 0x106},
+}};
+
+// Used by fres and ps_res.
+double ApproximateReciprocal(double val)
+{
+  // We are using namespace std scoped here because the Android NDK is complete trash as usual
+  // For 32bit targets(mips, ARMv7, x86) it doesn't provide an implementation of std::copysign
+  // but instead provides just global namespace copysign implementations.
+  // The workaround for this is to just use namespace std within this function's scope
+  // That way on real toolchains it will use the std:: variant like normal.
+  using namespace std;
+  union
+  {
+    double valf;
+    s64 vali;
+  };
+
+  valf = val;
+  s64 mantissa = vali & ((1LL << 52) - 1);
+  s64 sign = vali & (1ULL << 63);
+  s64 exponent = vali & (0x7FFLL << 52);
+
+  // Special case 0
+  if (mantissa == 0 && exponent == 0)
+    return copysign(std::numeric_limits<double>::infinity(), valf);
+
+  // Special case NaN-ish numbers
+  if (exponent == (0x7FFLL << 52))
+  {
+    if (mantissa == 0)
+      return copysign(0.0, valf);
+    return 0.0 + valf;
+  }
+
+  // Special case small inputs
+  if (exponent < (895LL << 52))
+    return copysign(std::numeric_limits<float>::max(), valf);
+
+  // Special case large inputs
+  if (exponent >= (1149LL << 52))
+    return copysign(0.0, valf);
+
+  exponent = (0x7FDLL << 52) - exponent;
+
+  int i = (int)(mantissa >> 37);
+  const auto& entry = fres_expected[i / 1024];
+  vali = sign | exponent;
+  vali |= (s64)(entry.m_base - (entry.m_dec * (i % 1024) + 1) / 2) << 29;
+  return valf;
+}
+
+}  // namespace Common