APInt: Add overload of isMask

[arsenm]

Summary

This mimics the version in MathExtras.h which isn't testing for a specific mask size.

[arsenm]

ping

[arsenm]

ping

[arsenm]

ping

[arsenm]

ping

[• tstellarAMD]

LGTM.

[arsenm]

r266101

include/llvm/ADT/APInt.h

 
 /// \returns true if the argument APInt value is a sequence of ones starting at
 /// the least significant bit with the remainder zero.
 inline bool isMask(unsigned numBits, const APInt &APIVal) {
   return numBits <= APIVal.getBitWidth() &&
          APIVal == APInt::getLowBitsSet(APIVal.getBitWidth(), numBits);
 }
 
+/// \returns true if the argument is a non-empty sequence of ones starting at
+/// the least significant bit with the remainder zero (32 bit version).
+/// Ex. isMask(0x0000FFFFU) == true.
+inline bool isMask(const APInt &Value) {
+  return (Value != 0) && ((Value + 1) & Value) == 0;
+}
+
 /// \brief Return true if the argument APInt value contains a sequence of ones
 /// with the remainder zero.
 inline bool isShiftedMask(unsigned numBits, const APInt &APIVal) {
   return isMask(numBits, (APIVal - APInt(numBits, 1)) | APIVal);
 }
 
 /// \brief Returns a byte-swapped representation of the specified APInt Value.
 inline APInt byteSwap(const APInt &APIVal) { return APIVal.byteSwap(); }

unittests/ADT/APIntTest.cpp

TEST(APIntTest, IsSplat) {
   EXPECT_TRUE(E.isSplat(1));
   EXPECT_TRUE(E.isSplat(2));
   EXPECT_TRUE(E.isSplat(4));
   EXPECT_TRUE(E.isSplat(8));
   EXPECT_TRUE(E.isSplat(16));
   EXPECT_TRUE(E.isSplat(32));
 }
 
+TEST(APIntTest, isMask) {
+  EXPECT_FALSE(APIntOps::isMask(APInt(32, 0x01010101)));
+  EXPECT_FALSE(APIntOps::isMask(APInt(32, 0xf0000000)));
+  EXPECT_FALSE(APIntOps::isMask(APInt(32, 0xffff0000)));
+  EXPECT_FALSE(APIntOps::isMask(APInt(32, 0xff << 1)));
+
+  for (int N : { 1, 2, 3, 4, 7, 8, 16, 32, 64, 127, 128, 129, 256 }) {
+    EXPECT_FALSE(APIntOps::isMask(APInt(N, 0)));
+
+    APInt One(N, 1);
+    for (int I = 1; I <= N; ++I) {
+      APInt MaskVal = One.shl(I) - 1;
+      EXPECT_TRUE(APIntOps::isMask(MaskVal));
+    }
+  }
+}
+
 #if defined(__clang__)
 // Disable the pragma warning from versions of Clang without -Wself-move
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunknown-pragmas"
 // Disable the warning that triggers on exactly what is being tested.
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wself-move"
 #endif