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https://github.com/patchzyy/wiicompiled
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patchzyy
54 lines
2.4 KiB
C++
54 lines
2.4 KiB
C++
#pragma once
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// FPSCR[NI] (non-IEEE flush-to-zero) modeled on the host FP environment, plus
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// the thread-local mirror of that state the hot paths read instead of MXCSR.
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#include "ppc_isa_config.h"
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#include <cstdint>
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// Software-flushing Gekko's single-precision denormals per op roughly doubled the THP IDCT
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// kernel's cycle count, so instead the runtime mirrors guest FPSCR[NI] into host MXCSR FTZ+DAZ
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// wherever FPSCR can change (PPC_Mtfs*, fiber context switches, CpuContextScope), making per-op
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// flushes free. Accepted deviations (same trade Dolphin makes): FTZ also flushes double
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// denormals unlike real NI, and a pre-round-flush edge near FLT_MIN rounds via cvtsd2ss instead.
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inline constexpr uint32_t kMkwMxcsrFlushToZeroBits = (1u << 15) | (1u << 6); // FTZ | DAZ
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inline thread_local bool g_mkwHostNiActive = false;
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// Same state in the form PpcForceSingleValueInline consumes: the pre-round subnormal threshold
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// while NI is active, 0.0 (identity, `|value| < 0.0` is always false) otherwise, so that path
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// needs no branch. Every writer of g_mkwHostNiActive must write this beside it in agreement.
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inline constexpr double kMkwNiFlushThreshold = 0x1p-126; // 0x3810000000000000
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inline thread_local double g_mkwNiFlushThreshold = 0.0;
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inline void MkwApplyHostNiMode(uint32_t fpscr) noexcept
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{
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const uint32_t csr = _mm_getcsr();
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const bool wantNi = (fpscr & 0x4u) != 0;
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const uint32_t want = wantNi
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? (csr | kMkwMxcsrFlushToZeroBits)
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: (csr & ~kMkwMxcsrFlushToZeroBits);
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if (want != csr)
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_mm_setcsr(want);
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// `want` has both bits set or both clear, so this is exactly
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// `(_mm_getcsr() & kMkwMxcsrFlushToZeroBits) != 0` after the write - the
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// mirror cannot disagree with the register even if the incoming CSR held
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// only one of the two bits.
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g_mkwHostNiActive = wantNi;
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g_mkwNiFlushThreshold = wantNi ? kMkwNiFlushThreshold : 0.0;
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}
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/// <summary>
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/// Restores a previously captured MXCSR value and re-derives the mirror from
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/// it. Every raw restore has to go through here; a bare _mm_setcsr would leave
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/// the mirror describing the FP environment that was just replaced.
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/// </summary>
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inline void MkwRestoreHostMxcsr(uint32_t csr) noexcept
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{
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_mm_setcsr(csr);
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const bool niActive = (csr & kMkwMxcsrFlushToZeroBits) != 0;
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g_mkwHostNiActive = niActive;
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g_mkwNiFlushThreshold = niActive ? kMkwNiFlushThreshold : 0.0;
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}
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