diff --git a/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp b/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
index afc1c9a920..671bd9fa9e 100644
--- a/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
+++ b/Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
@@ -1792,7 +1792,7 @@ void Jit64::divwx(UGeckoInstruction inst)
else
{
// Optimize signed 32-bit integer division by a constant
- Magic m = SignedDivisionConstants(divisor);
+ SignedMagic m = SignedDivisionConstants(divisor);
MOVSX(64, 32, RSCRATCH, Ra);
diff --git a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
index 43c90c9827..95f75a3f2a 100644
--- a/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
+++ b/Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
@@ -1675,7 +1675,7 @@ void JitArm64::divwx(UGeckoInstruction inst)
else
{
// Optimize signed 32-bit integer division by a constant
- Magic m = SignedDivisionConstants(divisor);
+ SignedMagic m = SignedDivisionConstants(divisor);
ARM64Reg WA = gpr.GetReg();
ARM64Reg WB = gpr.GetReg();
diff --git a/Source/Core/Core/PowerPC/JitCommon/DivUtils.cpp b/Source/Core/Core/PowerPC/JitCommon/DivUtils.cpp
index f1b6a1baf6..4648407e86 100644
--- a/Source/Core/Core/PowerPC/JitCommon/DivUtils.cpp
+++ b/Source/Core/Core/PowerPC/JitCommon/DivUtils.cpp
@@ -3,16 +3,18 @@
#include "Core/PowerPC/JitCommon/DivUtils.h"
+#include <algorithm>
+#include <bit>
#include <cstdlib>
namespace JitCommon
{
-Magic SignedDivisionConstants(s32 d)
+SignedMagic SignedDivisionConstants(s32 divisor)
{
const u32 two31 = 2147483648;
- const u32 ad = std::abs(d);
- const u32 t = two31 - (d < 0);
+ const u32 ad = std::abs(divisor);
+ const u32 t = two31 - (divisor < 0);
const u32 anc = t - 1 - t % ad;
u32 q1 = two31 / anc;
u32 r1 = two31 - q1 * anc;
@@ -44,13 +46,43 @@ Magic SignedDivisionConstants(s32 d)
delta = ad - r2;
} while (q1 < delta || (q1 == delta && r1 == 0));
- Magic mag;
+ SignedMagic mag;
mag.multiplier = q2 + 1;
- if (d < 0)
+ if (divisor < 0)
mag.multiplier = -mag.multiplier;
mag.shift = p - 32;
return mag;
}
+UnsignedMagic UnsignedDivisionConstants(u32 divisor)
+{
+ u32 shift = 31 - std::countl_zero(divisor);
+
+ u64 magic_dividend = 0x100000000ULL << shift;
+ u32 multiplier = magic_dividend / divisor;
+ u32 max_quotient = multiplier >> shift;
+
+ // Test for failure in round-up method
+ u32 round_up = (u64(multiplier + 1) * (max_quotient * divisor - 1)) >> (shift + 32);
+ bool fast = round_up == max_quotient - 1;
+
+ if (fast)
+ {
+ multiplier++;
+
+ // Use smallest magic number and shift amount possible
+ u32 trailing_zeroes = std::min(shift, u32(std::countr_zero(multiplier)));
+ multiplier >>= trailing_zeroes;
+ shift -= trailing_zeroes;
+ }
+
+ UnsignedMagic mag;
+ mag.multiplier = multiplier;
+ mag.shift = shift;
+ mag.fast = fast;
+
+ return mag;
+}
+
} // namespace JitCommon
diff --git a/Source/Core/Core/PowerPC/JitCommon/DivUtils.h b/Source/Core/Core/PowerPC/JitCommon/DivUtils.h
index 73d91426e1..2cc3f2e494 100644
--- a/Source/Core/Core/PowerPC/JitCommon/DivUtils.h
+++ b/Source/Core/Core/PowerPC/JitCommon/DivUtils.h
@@ -7,7 +7,7 @@
namespace JitCommon
{
-struct Magic
+struct SignedMagic
{
s32 multiplier;
u8 shift;
@@ -16,6 +16,27 @@ struct Magic
// Calculate the constants required to optimize a signed 32-bit integer division.
// Taken from The PowerPC Compiler Writer's Guide and LLVM.
// Divisor must not be -1, 0, 1 or INT_MIN.
-Magic SignedDivisionConstants(s32 divisor);
+SignedMagic SignedDivisionConstants(s32 divisor);
+
+struct UnsignedMagic
+{
+ u32 multiplier;
+ u8 shift;
+ bool fast;
+};
+
+/// Calculate the constants required to optimize an unsigned 32-bit integer
+/// division.
+/// Divisor must not be 0, 1, or a power of two.
+///
+/// Original implementation by calc84maniac.
+/// Results are the same as the approach laid out in Hacker's Delight, with an
+/// improvement for so-called uncooperative divisors (e.g. 7), as discovered by
+/// ridiculousfish.
+///
+/// See also:
+/// https://ridiculousfish.com/blog/posts/labor-of-division-episode-iii.html
+/// https://rubenvannieuwpoort.nl/posts/division-by-constant-unsigned-integers
+UnsignedMagic UnsignedDivisionConstants(u32 divisor);
} // namespace JitCommon
diff --git a/Source/UnitTests/Core/PowerPC/DivUtilsTest.cpp b/Source/UnitTests/Core/PowerPC/DivUtilsTest.cpp
index 894d0f628a..b218745849 100644
--- a/Source/UnitTests/Core/PowerPC/DivUtilsTest.cpp
+++ b/Source/UnitTests/Core/PowerPC/DivUtilsTest.cpp
@@ -9,12 +9,12 @@ using namespace JitCommon;
TEST(DivUtils, Signed)
{
- Magic m3 = SignedDivisionConstants(3);
- Magic m5 = SignedDivisionConstants(5);
- Magic m7 = SignedDivisionConstants(7);
- Magic minus3 = SignedDivisionConstants(-3);
- Magic minus5 = SignedDivisionConstants(-5);
- Magic minus7 = SignedDivisionConstants(-7);
+ SignedMagic m3 = SignedDivisionConstants(3);
+ SignedMagic m5 = SignedDivisionConstants(5);
+ SignedMagic m7 = SignedDivisionConstants(7);
+ SignedMagic minus3 = SignedDivisionConstants(-3);
+ SignedMagic minus5 = SignedDivisionConstants(-5);
+ SignedMagic minus7 = SignedDivisionConstants(-7);
EXPECT_EQ(0x55555556, m3.multiplier);
EXPECT_EQ(0, m3.shift);
@@ -30,3 +30,32 @@ TEST(DivUtils, Signed)
EXPECT_EQ(0x6DB6DB6D, minus7.multiplier);
EXPECT_EQ(2, minus7.shift);
}
+
+TEST(DivUtils, Unsigned)
+{
+ UnsignedMagic m3 = UnsignedDivisionConstants(3);
+ UnsignedMagic m5 = UnsignedDivisionConstants(5);
+ UnsignedMagic m7 = UnsignedDivisionConstants(7);
+ UnsignedMagic m9 = UnsignedDivisionConstants(9);
+ UnsignedMagic m19 = UnsignedDivisionConstants(19);
+
+ EXPECT_EQ(0xAAAAAAABU, m3.multiplier);
+ EXPECT_EQ(1, m3.shift);
+ EXPECT_TRUE(m3.fast);
+
+ EXPECT_EQ(0xCCCCCCCDU, m5.multiplier);
+ EXPECT_EQ(2, m5.shift);
+ EXPECT_TRUE(m5.fast);
+
+ EXPECT_EQ(0x92492492U, m7.multiplier);
+ EXPECT_EQ(2, m7.shift);
+ EXPECT_FALSE(m7.fast);
+
+ EXPECT_EQ(0x38E38E39U, m9.multiplier);
+ EXPECT_EQ(1, m9.shift);
+ EXPECT_TRUE(m9.fast);
+
+ EXPECT_EQ(0xD79435E5U, m19.multiplier);
+ EXPECT_EQ(4, m19.shift);
+ EXPECT_FALSE(m19.fast);
+}