Add a ceilLogBase2 function to APInt.

llvm-svn: 83932

2 files changed, 16 insertions, 0 deletions

diff --git a/llvm/include/llvm/ADT/APInt.h b/llvm/include/llvm/ADT/APInt.h
index 6c418bda62d..88aa9956d93 100644
--- a/llvm/include/llvm/ADT/APInt.h
+++ b/llvm/include/llvm/ADT/APInt.h
@@ -1234,6 +1234,11 @@ public:
     return BitWidth - 1 - countLeadingZeros();
   }
 
+  /// @returns the ceil log base 2 of this APInt.
+  unsigned ceilLogBase2() const {
+    return BitWidth - (*this - 1).countLeadingZeros();
+  }
+
   /// @returns the log base 2 of this APInt if its an exact power of two, -1
   /// otherwise
   int32_t exactLogBase2() const {
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 24a3d9b4ade..7b03d0f00c8 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -315,6 +315,17 @@ TEST(APIntTest, StringBitsNeeded16) {
   EXPECT_EQ(9U, APInt::getBitsNeeded("-20", 16));
 }
 
+TEST(APIntTest, Log2) {
+  EXPECT_EQ(APInt(15, 7).logBase2(), 2);
+  EXPECT_EQ(APInt(15, 7).ceilLogBase2(), 3);
+  EXPECT_EQ(APInt(15, 7).exactLogBase2(), -1);
+  EXPECT_EQ(APInt(15, 8).logBase2(), 3);
+  EXPECT_EQ(APInt(15, 8).ceilLogBase2(), 3);
+  EXPECT_EQ(APInt(15, 8).exactLogBase2(), 3);
+  EXPECT_EQ(APInt(15, 9).logBase2(), 3);
+  EXPECT_EQ(APInt(15, 9).ceilLogBase2(), 4);
+  EXPECT_EQ(APInt(15, 9).exactLogBase2(), -1);
+}
 
 #ifdef GTEST_HAS_DEATH_TEST
 TEST(APIntTest, StringDeath) {