From 46f829ee25ed0cba401cd759da684d3c4aa1478a Mon Sep 17 00:00:00 2001
From: Michael Gottesman <mgottesman@apple.com>
Date: Fri, 13 Dec 2013 20:47:37 +0000
Subject: [PATCH] [block-freq] Add the method APInt::nearestLogBase2().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197272 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/APInt.h    | 13 +++++++++++
 unittests/ADT/APIntTest.cpp | 44 +++++++++++++++++++++++++++++++++----
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/llvm/ADT/APInt.h b/include/llvm/ADT/APInt.h
index 2073fa08cbf..2bb5c3e2a12 100644
--- a/include/llvm/ADT/APInt.h
+++ b/include/llvm/ADT/APInt.h
@@ -1507,6 +1507,19 @@ public:
     return BitWidth - (*this - 1).countLeadingZeros();
   }
 
+  /// \returns the nearest log base 2 of this APInt. Ties round up.
+  unsigned nearestLogBase2() const {
+    // This is implemented by taking the normal log 2 of a number and adding 1
+    // to it if MSB - 1 is set.
+
+    // We follow the model from logBase2 that logBase2(0) == UINT32_MAX. This
+    // works since if we have 0, MSB will be 0. Then we subtract one yielding
+    // UINT32_MAX. Finally extractBit of MSB - 1 will be UINT32_MAX implying
+    // that we get BitWidth - 1.
+    unsigned lg = logBase2();
+    return lg + unsigned(extractBit(std::min(lg - 1, BitWidth - 1)));
+  }
+
   /// \returns the log base 2 of this APInt if its an exact power of two, -1
   /// otherwise
   int32_t exactLogBase2() const {
diff --git a/unittests/ADT/APIntTest.cpp b/unittests/ADT/APIntTest.cpp
index 1d330f0d369..36cbd868a2e 100644
--- a/unittests/ADT/APIntTest.cpp
+++ b/unittests/ADT/APIntTest.cpp
@@ -609,10 +609,10 @@ TEST(APIntTest, extractBit) {
 
   // Multiword check.
   integerPart E2[4] = {
-    0xeb6eb136591cba21ULL,
-    0x7b9358bd6a33f10aULL,
-    0x7e7ffa5eadd8846ULL,
-    0x305f341ca00b613dULL
+    0xEB6EB136591CBA21ULL,
+    0x7B9358BD6A33F10AULL,
+    0x7E7FFA5EADD8846ULL,
+    0x305F341CA00B613DULL
   };
   APInt A2(integerPartWidth*4, ArrayRef<integerPart>(E2, 4));
   for (unsigned i = 0; i < 4; ++i) {
@@ -623,4 +623,40 @@ TEST(APIntTest, extractBit) {
   }
 }
 
+TEST(APIntTest, nearestLogBase2) {
+  // Single word check.  
+
+  // Test round up.
+  uint64_t I1 = 0x1800001;
+  APInt A1(64, I1);
+  EXPECT_EQ(A1.nearestLogBase2(), A1.ceilLogBase2());
+
+  // Test round down.
+  uint64_t I2 = 0x1000011;
+  APInt A2(64, I2);
+  EXPECT_EQ(A2.nearestLogBase2(), A2.logBase2());
+
+  // Test ties round up.
+  uint64_t I3 = 0x1800000;
+  APInt A3(64, I3);
+  EXPECT_EQ(A3.nearestLogBase2(), A3.ceilLogBase2());
+
+  // Multiple word check.
+
+  // Test round up.
+  integerPart I4[4] = {0x0, 0xF, 0x18, 0x0};
+  APInt A4(integerPartWidth*4, ArrayRef<integerPart>(I4, 4));
+  EXPECT_EQ(A4.nearestLogBase2(), A4.ceilLogBase2());
+
+  // Test round down.
+  integerPart I5[4] = {0x0, 0xF, 0x10, 0x0};
+  APInt A5(integerPartWidth*4, ArrayRef<integerPart>(I5, 4));
+  EXPECT_EQ(A5.nearestLogBase2(), A5.logBase2());
+
+  // Test ties round up.
+  uint64_t I6[4] = {0x0, 0x0, 0x0, 0x18};
+  APInt A6(integerPartWidth*4, ArrayRef<integerPart>(I6, 4));
+  EXPECT_EQ(A6.nearestLogBase2(), A6.ceilLogBase2());
+}
+
 }
-- 
2.34.1