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X86 : Cleanup comments, moved Parity calculation into a macro.

This commit is contained in:
PatrickvL 2017-11-22 15:06:42 +01:00
parent 69cce01cc6
commit 8737046c84
1 changed files with 5 additions and 13 deletions
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18
src/CxbxKrnl/EmuX86.cpp
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@ -751,15 +751,6 @@ inline void EmuX86_SetFlags_OSZAP
);
}
// Calculate Parity flag, based on "Compute parity in parallel" method from
// http://graphics.stanford.edu/~seander/bithacks.html#ParityParallel
inline bool ComputeParityInParallel(uint8_t v)
{
// Note : If input isn't a byte, do : v &= 255;
v ^= v >> 4;
return (0x6996 >> (v & 0xf)) & 1;
}
// EFLAGS Cross-Reference : http://datasheets.chipdb.org/Intel/x86/Intel%20Architecture/EFLAGS.PDF
// TODO : Review these CPU flag calculations, maybe peek at how MAME or Bochs does this.
@ -767,13 +758,14 @@ inline bool ComputeParityInParallel(uint8_t v)
#define BitSize (info.ops[0].size) // Note : Uses 'info' argument of functions using this macro
// TODO : Use templates for these, so 8, 16 and 32 bit versions will compile into efficient bit manipulations
#define OF_Add(r,s,d) (((r ^ s) & (r ^ d)) >> (BitSize-1)) & 1 // Result, Dest, Src
#define OF_Sub(r,s,d) (((d ^ s) & (d ^ r)) >> (BitSize-1)) & 1 // Result, Dest, Src
#define OF_Add(r,s,d) (((r ^ s) & (r ^ d)) >> (BitSize-1)) & 1 // Result, Src, Dest
#define OF_Sub(r,s,d) (((d ^ s) & (r ^ d)) >> (BitSize-1)) & 1 // Result, Src, Dest
#define SFCalc(result) (result >> (BitSize-1)) & 1
#define ZFCalc(result) (result == 0)
#define AFCalc(r,s,d) ((r ^ s ^ d)>> 3) & 1
#define PFCalc(result) (ComputeParityInParallel(static_cast<uint8_t>(result)))
#define AFCalc(r,s,d) ((r ^ s ^ d) >> 3) & 1 // Result, Src, Dest
#define PFCalc(result) (0x6996 >> ((result ^ (result >> 4)) & 0xF)) & 1 // See http://graphics.stanford.edu/~seander/bithacks.html#ParityParallel
#define CFCalc(result) (result >> BitSize) & 1 // TODO : Instead of looking at an actual overflow bit, use high bit of (result XOR dest XOR src)
// Flags calculated : Overflow (for addition or subtraction), Sign, Zero, Adjust, Parity and Carry
// See http://x86.renejeschke.de/ for affected CPU flags per instruction