From d1e841f55db0a2f25341045196c7830128c9f144 Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Sun, 26 Apr 2020 18:33:35 +1000
Subject: [PATCH] GTE: Use intrinsic CountLeadingZeros()
Super tiny micro-optimization.
---
src/core/gte.cpp | 40 +++++++---------------------------------
1 file changed, 7 insertions(+), 33 deletions(-)
diff --git a/src/core/gte.cpp b/src/core/gte.cpp
index 2513d1b10..454623177 100644
--- a/src/core/gte.cpp
+++ b/src/core/gte.cpp
@@ -1,41 +1,15 @@
#include "gte.h"
+#include "common/bitutils.h"
#include <algorithm>
#include <array>
-// TODO: Optimize, intrinsics?
-static inline constexpr u32 CountLeadingZeros(u16 value)
+ALWAYS_INLINE u32 CountLeadingBits(u32 value)
{
- u32 count = 0;
- for (u32 i = 0; i < 16 && (value & UINT16_C(0x8000)) == 0; i++)
- {
- count++;
- value <<= 1;
- }
+ // if top-most bit is set, we want to count ones not zeros
+ if (value & UINT32_C(0x80000000))
+ value ^= UINT32_C(0xFFFFFFFF);
- return count;
-}
-
-static inline constexpr u32 CountLeadingBits(u32 value)
-{
- u32 count = 0;
- if ((value & UINT32_C(0x80000000)) != 0)
- {
- for (u32 i = 0; i < 32 && ((value & UINT32_C(0x80000000)) != 0); i++)
- {
- count++;
- value <<= 1;
- }
- }
- else
- {
- for (u32 i = 0; i < 32 && (value & UINT32_C(0x80000000)) == 0; i++)
- {
- count++;
- value <<= 1;
- }
- }
-
- return count;
+ return (value == 0u) ? 32 : CountLeadingZeros(value);
}
namespace GTE {
@@ -365,7 +339,7 @@ u32 Core::UNRDivide(u32 lhs, u32 rhs)
return 0x1FFFF;
}
- const u32 shift = CountLeadingZeros(static_cast<u16>(rhs));
+ const u32 shift = (rhs == 0) ? 16 : CountLeadingZeros(static_cast<u16>(rhs));
lhs <<= shift;
rhs <<= shift;