[PATCH] D17649: APInt: Add overload of isMask

[Matt Arsenault via llvm-commits]

arsenm created this revision.
arsenm added a subscriber: llvm-commits.

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

http://reviews.llvm.org/D17649

Files:
  include/llvm/ADT/APInt.h
  unittests/ADT/APIntTest.cpp

Index: unittests/ADT/APIntTest.cpp
===================================================================
--- unittests/ADT/APIntTest.cpp
+++ unittests/ADT/APIntTest.cpp
@@ -994,6 +994,23 @@
   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
Index: include/llvm/ADT/APInt.h
===================================================================
--- include/llvm/ADT/APInt.h
+++ include/llvm/ADT/APInt.h
@@ -1778,6 +1778,13 @@
          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) {


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