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[APInt] Introduce carry-less multiply primitives (#168527)
In line with a std proposal to introduce std::clmul, and in preparation to introduce a clmul intrinsic, implement carry-less multiply primitives for APIntOps, clmul[rh]. Ref: https://isocpp.org/files/papers/P3642R3.html
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‎llvm/include/llvm/ADT/APInt.h‎

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@@ -2440,6 +2440,27 @@ LLVM_ABI APInt fshl(const APInt &Hi, const APInt &Lo, const APInt &Shift);
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/// (4) fshr(i8 255, i8 0, i8 9) = fshr(i8 255, i8 0, i8 1) // 9 % 8
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LLVM_ABI APInt fshr(const APInt &Hi, const APInt &Lo, const APInt &Shift);
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/// Perform a carry-less multiply, also known as XOR multiplication, and return
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/// low-bits. All arguments and result have the same bitwidth.
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///
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/// Examples:
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/// (1) clmul(i4 1, i4 2) = 2
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/// (2) clmul(i4 5, i4 6) = 14
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/// (3) clmul(i4 -4, i4 2) = -8
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/// (4) clmul(i4 -4, i4 -5) = 4
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LLVM_ABI APInt clmul(const APInt &LHS, const APInt &RHS);
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/// Perform a reversed carry-less multiply.
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///
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/// clmulr(a, b) = bitreverse(clmul(bitreverse(a), bitreverse(b)))
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LLVM_ABI APInt clmulr(const APInt &LHS, const APInt &RHS);
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/// Perform a carry-less multiply, and return high-bits. All arguments and
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/// result have the same bitwidth.
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///
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/// clmulh(a, b) = clmulr(a, b) >> 1
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LLVM_ABI APInt clmulh(const APInt &LHS, const APInt &RHS);
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} // namespace APIntOps
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// See friend declaration above. This additional declaration is required in

‎llvm/lib/Support/APInt.cpp‎

Lines changed: 21 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15,10 +15,10 @@
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/FoldingSet.h"
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#include "llvm/ADT/Hashing.h"
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#include "llvm/ADT/Sequence.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/bit.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/Support/Alignment.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
@@ -3187,3 +3187,23 @@ APInt llvm::APIntOps::fshr(const APInt &Hi, const APInt &Lo,
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return Lo;
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return Hi.shl(Hi.getBitWidth() - ShiftAmt) | Lo.lshr(ShiftAmt);
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}
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APInt llvm::APIntOps::clmul(const APInt &LHS, const APInt &RHS) {
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assert(LHS.getBitWidth() == RHS.getBitWidth());
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unsigned BW = LHS.getBitWidth();
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APInt Result(BW, 0);
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for (unsigned I : seq<unsigned>(BW))
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if (RHS[I])
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Result ^= LHS.shl(I);
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return Result;
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}
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APInt llvm::APIntOps::clmulr(const APInt &LHS, const APInt &RHS) {
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assert(LHS.getBitWidth() == RHS.getBitWidth());
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return clmul(LHS.reverseBits(), RHS.reverseBits()).reverseBits();
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}
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APInt llvm::APIntOps::clmulh(const APInt &LHS, const APInt &RHS) {
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assert(LHS.getBitWidth() == RHS.getBitWidth());
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return clmulr(LHS, RHS).lshr(1);
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}

‎llvm/unittests/ADT/APIntTest.cpp‎

Lines changed: 83 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3823,4 +3823,87 @@ TEST(APIntTest, Fshr) {
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-8193);
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}
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TEST(APIntTest, clmul) {
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EXPECT_EQ(APIntOps::clmul(APInt(4, 1), APInt(4, 2)).getZExtValue(), 2U);
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EXPECT_EQ(APIntOps::clmul(APInt(4, 5), APInt(4, 6)).getZExtValue(), 14U);
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EXPECT_EQ(APIntOps::clmul(APInt(4, -4, /*isSigned*/ true),
3830+
APInt(4, 2, /*isSigned*/ false))
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.getSExtValue(),
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-8);
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EXPECT_EQ(APIntOps::clmul(APInt(4, -4, /*isSigned*/ true),
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APInt(4, -5, /*isSigned*/ true))
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.getSExtValue(),
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4);
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EXPECT_EQ(APIntOps::clmul(APInt(8, 0), APInt(8, 255)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmul(APInt(8, 15), APInt(8, 15)).getZExtValue(), 85U);
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EXPECT_EQ(APIntOps::clmul(APInt(8, 1), APInt(8, 2)).getZExtValue(), 2U);
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EXPECT_EQ(APIntOps::clmul(APInt(64, 0, /*isSigned*/ true),
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APInt(64, 9223372036854775807, /*isSigned*/ true))
3842+
.getSExtValue(),
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0);
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EXPECT_EQ(APIntOps::clmul(APInt(64, 1, /*isSigned*/ true),
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APInt(64, 2, /*isSigned*/ true))
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.getSExtValue(),
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2);
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EXPECT_EQ(APIntOps::clmul(APInt(16, -2, /*isSigned*/ true),
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APInt(16, -1, /*isSigned*/ true))
3850+
.getSExtValue(),
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-21846);
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}
3853+
3854+
TEST(APIntTest, clmulr) {
3855+
EXPECT_EQ(APIntOps::clmulr(APInt(4, 1), APInt(4, 2)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulr(APInt(4, 5), APInt(4, 6)).getZExtValue(), 3U);
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EXPECT_EQ(APIntOps::clmulr(APInt(4, -4, /*isSigned*/ true),
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APInt(4, 2, /*isSigned*/ false))
3859+
.getSExtValue(),
3860+
3);
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EXPECT_EQ(APIntOps::clmulr(APInt(4, -4, /*isSigned*/ true),
3862+
APInt(4, -5, /*isSigned*/ true))
3863+
.getSExtValue(),
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-2);
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EXPECT_EQ(APIntOps::clmulr(APInt(8, 0), APInt(8, 255)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulr(APInt(8, 15), APInt(8, 15)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulr(APInt(8, 1), APInt(8, 2)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulr(APInt(64, 0, /*isSigned*/ true),
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APInt(64, 9223372036854775807, /*isSigned*/ true))
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.getSExtValue(),
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0);
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EXPECT_EQ(APIntOps::clmulr(APInt(64, 1, /*isSigned*/ true),
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APInt(64, 2, /*isSigned*/ true))
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.getSExtValue(),
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0);
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EXPECT_EQ(APIntOps::clmulr(APInt(16, -2, /*isSigned*/ true),
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APInt(16, -1, /*isSigned*/ true))
3878+
.getSExtValue(),
3879+
-21845);
3880+
}
3881+
3882+
TEST(APIntTest, clmulh) {
3883+
EXPECT_EQ(APIntOps::clmulh(APInt(4, 1), APInt(4, 2)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulh(APInt(4, 5), APInt(4, 6)).getZExtValue(), 1U);
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EXPECT_EQ(APIntOps::clmulh(APInt(4, -4, /*isSigned*/ true),
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APInt(4, 2, /*isSigned*/ false))
3887+
.getSExtValue(),
3888+
1);
3889+
EXPECT_EQ(APIntOps::clmulh(APInt(4, -4, /*isSigned*/ true),
3890+
APInt(4, -5, /*isSigned*/ true))
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.getSExtValue(),
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7);
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EXPECT_EQ(APIntOps::clmulh(APInt(8, 0), APInt(8, 255)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulh(APInt(8, 15), APInt(8, 15)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulh(APInt(8, 1), APInt(8, 2)).getZExtValue(), 0U);
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EXPECT_EQ(APIntOps::clmulh(APInt(64, 0, /*isSigned*/ true),
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APInt(64, 9223372036854775807, /*isSigned*/ true))
3898+
.getSExtValue(),
3899+
0);
3900+
EXPECT_EQ(APIntOps::clmulh(APInt(64, 1, /*isSigned*/ true),
3901+
APInt(64, 2, /*isSigned*/ true))
3902+
.getSExtValue(),
3903+
0);
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EXPECT_EQ(APIntOps::clmulh(APInt(16, -2, /*isSigned*/ true),
3905+
APInt(16, -1, /*isSigned*/ true))
3906+
.getSExtValue(),
3907+
21845);
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}
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} // end anonymous namespace

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