PPU: implement accurate FRES

Implemented with an accurate lookup table.

rpcs3/Emu/Cell/Common.h

@@ -17,6 +17,138 @@ inline int fexpf(float x)
 	return (std::bit_cast<u32>(x) >> 23) & 0xff;
 }
 
+constexpr u32 ppu_fres_mantissas[128] =
+{
+	0x007f0000,
+	0x007d0800,
+	0x007b1800,
+	0x00793000,
+	0x00775000,
+	0x00757000,
+	0x0073a000,
+	0x0071e000,
+	0x00700000,
+	0x006e4000,
+	0x006ca000,
+	0x006ae000,
+	0x00694000,
+	0x00678000,
+	0x00660000,
+	0x00646000,
+	0x0062c000,
+	0x00614000,
+	0x005fc000,
+	0x005e4000,
+	0x005cc000,
+	0x005b4000,
+	0x0059c000,
+	0x00584000,
+	0x00570000,
+	0x00558000,
+	0x00540000,
+	0x0052c000,
+	0x00518000,
+	0x00500000,
+	0x004ec000,
+	0x004d8000,
+	0x004c0000,
+	0x004b0000,
+	0x00498000,
+	0x00488000,
+	0x00474000,
+	0x00460000,
+	0x0044c000,
+	0x00438000,
+	0x00428000,
+	0x00418000,
+	0x00400000,
+	0x003f0000,
+	0x003e0000,
+	0x003d0000,
+	0x003bc000,
+	0x003ac000,
+	0x00398000,
+	0x00388000,
+	0x00378000,
+	0x00368000,
+	0x00358000,
+	0x00348000,
+	0x00338000,
+	0x00328000,
+	0x00318000,
+	0x00308000,
+	0x002f8000,
+	0x002ec000,
+	0x002e0000,
+	0x002d0000,
+	0x002c0000,
+	0x002b0000,
+	0x002a0000,
+	0x00298000,
+	0x00288000,
+	0x00278000,
+	0x0026c000,
+	0x00260000,
+	0x00250000,
+	0x00244000,
+	0x00238000,
+	0x00228000,
+	0x00220000,
+	0x00210000,
+	0x00200000,
+	0x001f8000,
+	0x001e8000,
+	0x001e0000,
+	0x001d0000,
+	0x001c8000,
+	0x001b8000,
+	0x001b0000,
+	0x001a0000,
+	0x00198000,
+	0x00190000,
+	0x00180000,
+	0x00178000,
+	0x00168000,
+	0x00160000,
+	0x00158000,
+	0x00148000,
+	0x00140000,
+	0x00138000,
+	0x00128000,
+	0x00120000,
+	0x00118000,
+	0x00108000,
+	0x00100000,
+	0x000f8000,
+	0x000f0000,
+	0x000e0000,
+	0x000d8000,
+	0x000d0000,
+	0x000c8000,
+	0x000b8000,
+	0x000b0000,
+	0x000a8000,
+	0x000a0000,
+	0x00098000,
+	0x00090000,
+	0x00080000,
+	0x00078000,
+	0x00070000,
+	0x00068000,
+	0x00060000,
+	0x00058000,
+	0x00050000,
+	0x00048000,
+	0x00040000,
+	0x00038000,
+	0x00030000,
+	0x00028000,
+	0x00020000,
+	0x00018000,
+	0x00010000,
+	0x00000000,
+};
+
 constexpr u32 ppu_frsqrte_mantissas[16] =
 {
 	0x000f1000u, 0x000d8000u, 0x000c0000u, 0x000a8000u,

rpcs3/Emu/Cell/PPUInterpreter.cpp

@@ -6176,9 +6176,16 @@ auto FRES()
 	if constexpr (Build == 0xf1a6)
 		return ppu_exec_select<Flags...>::template select<set_fpcc>();
 
-	static const auto exec = [](ppu_thread& ppu, ppu_opcode_t op) {
-	ppu.fpr[op.frd] = f32(1.0 / ppu.fpr[op.frb]);
-	ppu_set_fpcc<Flags...>(ppu, ppu.fpr[op.frd], 0.);
+	static const auto exec = [](ppu_thread& ppu, ppu_opcode_t op)
+	{
+		const f64 a = ppu.fpr[op.frb];
+		const u64 b = std::bit_cast<u64>(a);
+		const u64 e = (b >> 52) & 0x7ff; // double exp
+		const u64 i = (b >> 45) & 0x7f; // mantissa LUT index
+		const u64 r = e >= (0x3ff + 0x80) ? 0 : (0x7ff - 2 - e) << 52 | u64{ppu_fres_mantissas[i]} << (32 - 3);
+
+		ppu.fpr[op.frd] = f32(std::bit_cast<f64>(a == a ? (b & 0x8000'0000'0000'0000) | r : (0x8'0000'0000'0000 | b)));
+		ppu_set_fpcc<Flags...>(ppu, ppu.fpr[op.frd], 0.);
 	};
 	RETURN_(ppu, op);
 }

rpcs3/Emu/Cell/PPUTranslator.cpp

@@ -3991,9 +3991,22 @@ void PPUTranslator::FSQRTS(ppu_opcode_t op)
 
 void PPUTranslator::FRES(ppu_opcode_t op)
 {
-	const auto b = GetFpr(op.frb, 32);
-	const auto result = m_ir->CreateFDiv(ConstantFP::get(GetType<f32>(), 1.0), b);
-	SetFpr(op.frd, result);
+	if (!m_fres_table)
+	{
+		m_fres_table = new GlobalVariable(*m_module, ArrayType::get(GetType<u32>(), 128), true, GlobalValue::PrivateLinkage, ConstantDataArray::get(m_context, ppu_fres_mantissas));
+	}
+
+	const auto a = GetFpr(op.frb);
+	const auto b = bitcast<u64>(a);
+	const auto n = m_ir->CreateFCmpUNO(a, a); // test for NaN
+	const auto e = m_ir->CreateAnd(m_ir->CreateLShr(b, 52), 0x7ff); // double exp
+	const auto i = m_ir->CreateAnd(m_ir->CreateLShr(b, 45), 0x7f); // mantissa LUT index
+	const auto m = m_ir->CreateShl(ZExt(m_ir->CreateLoad(m_ir->CreateGEP(m_fres_table, {m_ir->getInt64(0), i}))), 29);
+	const auto c = m_ir->CreateICmpUGE(e, m_ir->getInt64(0x3ff + 0x80)); // test for INF
+	const auto x = m_ir->CreateShl(m_ir->CreateSub(m_ir->getInt64(0x7ff - 2), e), 52);
+	const auto s = m_ir->CreateSelect(c, m_ir->getInt64(0), m_ir->CreateOr(x, m));
+	const auto r = bitcast<f64>(m_ir->CreateSelect(n, m_ir->CreateOr(b, 0x8'0000'0000'0000), m_ir->CreateOr(s, m_ir->CreateAnd(b, 0x8000'0000'0000'0000))));
+	SetFpr(op.frd, m_ir->CreateFPTrunc(r, GetType<f32>()));
 
 	//m_ir->CreateStore(GetUndef<bool>(), m_fpscr_fr);
 	//m_ir->CreateStore(GetUndef<bool>(), m_fpscr_fi);
@@ -4002,7 +4015,7 @@ void PPUTranslator::FRES(ppu_opcode_t op)
 	//SetFPSCRException(m_fpscr_ux, Call(GetType<bool>(), m_pure_attr, "__fres_get_ux", b));
 	//SetFPSCRException(m_fpscr_zx, Call(GetType<bool>(), m_pure_attr, "__fres_get_zx", b));
 	//SetFPSCRException(m_fpscr_vxsnan, Call(GetType<bool>(), m_pure_attr, "__fres_get_vxsnan", b));
-	SetFPRF(result, op.rc != 0);
+	SetFPRF(r, op.rc != 0);
 }
 
 void PPUTranslator::FMULS(ppu_opcode_t op)

rpcs3/Emu/Cell/PPUTranslator.h

@@ -56,6 +56,7 @@ class PPUTranslator final : public cpu_translator
 
 	llvm::Value* m_mtocr_table{};
 	llvm::Value* m_frsqrte_table{};
+	llvm::Value* m_fres_table{};
 
 	llvm::Value* m_globals[175];
 	llvm::Value** const m_g_cr = m_globals + 99;