Consolidate all of the various log2 computing functions into MathExtras.h.

Also, provide accelerated implementations when building with GCC.
Patch contributed by Jim Laskey!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22591 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 131 insertions, 18 deletions

diff --git a/include/llvm/Support/MathExtras.h b/include/llvm/Support/MathExtras.h
index 1f5f86b..1e000b6 100644
--- a/include/llvm/Support/MathExtras.h
+++ b/include/llvm/Support/MathExtras.h
@@ -18,32 +18,145 @@
 
 namespace llvm {
 
-#if defined(log2)
-# undef log2
+// NOTE: The following support functions use the _32/_64 extensions instead of type 
+// overloading so that signed and unsigned integers can be used without ambiguity.
+
+
+// Hi_32 - This function returns the high 32 bits of a 64 bit value.
+inline unsigned Hi_32(uint64_t Value) {
+  return (unsigned)(Value >> 32);
+}
+
+// Lo_32 - This function returns the low 32 bits of a 64 bit value.
+inline unsigned Lo_32(uint64_t Value) {
+  return (unsigned)Value;
+}
+
+// is?Type - these functions produce optimal testing for integer data types.
+inline bool isInt8  (int Value)     { return (  signed char )Value == Value; }
+inline bool isUInt8 (int Value)     { return (unsigned char )Value == Value; }
+inline bool isInt16 (int Value)     { return (  signed short)Value == Value; }
+inline bool isUInt16(int Value)     { return (unsigned short)Value == Value; }
+inline bool isInt32 (int64_t Value) { return (  signed int  )Value == Value; }
+inline bool isUInt32(int64_t Value) { return (unsigned int  )Value == Value; }
+
+// isMask_32 - This function returns true if the argument is a sequence of ones starting 
+// at the least significant bit with the remainder zero (32 bit version.)
+// Ex. isMask_32(0x0000FFFFU) == true.
+inline const bool isMask_32(unsigned Value) {
+  return Value && ((Value + 1) & Value) == 0;
+}
+
+// isMask_64 - This function returns true if the argument is a sequence of ones starting 
+// at the least significant bit with the remainder zero (64 bit version.)
+inline const bool isMask_64(uint64_t Value) {
+  return Value && ((Value + 1) & Value) == 0;
+}
+
+// isShiftedMask_32 - This function returns true if the argument contains a sequence of ones 
+// with the remainder zero (32 bit version.)
+// Ex. isShiftedMask_32(0x0000FF00U) == true.
+inline const bool isShiftedMask_32(unsigned Value) {
+  return isMask_32((Value - 1) | Value);
+}
+
+// isShiftedMask_64 - This function returns true if the argument contains a sequence of ones 
+// with the remainder zero (64 bit version.)
+inline const bool isShiftedMask_64(uint64_t Value) {
+  return isMask_64((Value - 1) | Value);
+}
+
+// isPowerOf2_32 - This function returns true if the argument is a power of two > 0.
+// Ex. isPowerOf2_32(0x00100000U) == true (32 bit edition.)
+inline bool isPowerOf2_32(unsigned Value) {
+  return Value && !(Value & (Value - 1));
+}
+
+// isPowerOf2_64 - This function returns true if the argument is a power of two > 0
+// (64 bit edition.)
+inline bool isPowerOf2_64(uint64_t Value) {
+  return Value && !(Value & (Value - 1LL));
+}
+
+// CountLeadingZeros_32 - this function performs the platform optimal form
+// of counting the number of zeros from the most significant bit to the first one bit.
+// Ex. CountLeadingZeros_32(0x00F000FF) == 8.
+// Returns 32 if the word is zero.
+inline unsigned CountLeadingZeros_32(unsigned Value) {
+  unsigned Count; // result
+  #if __GNUC__ >= 4
+    // PowerPC is defined for __builtin_clz(0)
+    #if defined(__ppc__) || defined(__ppc64__)
+      if (!Value) return 32;
 #endif
+    Count = __builtin_clz(Value);
+  #else
+    if (!Value) return 32;
+    Count = 0;
+    // bisecton method for count leading zeros
+    for (unsigned Shift = 32 >> 1; Shift; Shift >>= 1) {
+        unsigned Tmp = Value >> Shift;
+        if (Tmp) {
+            Count |= Shift;
+            Value = Tmp;
+        }
+    }
+  #endif
+  return Count;
+}
 
-inline unsigned log2(uint64_t C) {
-  unsigned getPow;
-  for (getPow = 0; C > 1; ++getPow)
-    C >>= 1;
-  return getPow;
+// CountLeadingZeros_64 - This function performs the platform optimal form
+// of counting the number of zeros from the most significant bit to the first one bit
+// (64 bit edition.)
+// Returns 64 if the word is zero.
+inline unsigned CountLeadingZeros_64(uint64_t Value) {
+  unsigned Count; // result
+  #if __GNUC__ >= 4
+    // PowerPC is defined for __builtin_clzll(0)
+    #if defined(__ppc__) || defined(__ppc64__)
+      if (!Value) return 64;
+    #endif
+    Count = __builtin_clzll(Value);
+  #elif sizeof(long) == sizeof(int64_t)
+    if (!Value) return 64;
+    Count = 0;
+    // bisecton method for count leading zeros
+    for (uint64_t Shift = 64 >> 1; Shift; Shift >>= 1) {
+      uint64_t Tmp = Value >> Shift;
+      if (Tmp) {
+        Count |= Shift;
+        Value = Tmp;
+      }
 }
+  #else
+    // get hi portion
+    unsigned Hi = Hi_32(Value);
 
-inline unsigned log2(unsigned C) {
-  unsigned getPow;
-  for (getPow = 0; C > 1; ++getPow)
-    C >>= 1;
-  return getPow;
+    // if some bits in hi portion
+    if (Hi) {
+        // leading zeros in hi portion plus all bits in lo portion
+        Count = CountLeadingZeros_32(Hi) + 32;
+    } else {
+        // get lo portion
+        unsigned Lo = Lo_32(Value);
+        // same as 32 bit value
+        Count = CountLeadingZeros_32(Lo);
+    }
+  #endif
+  return Count;
 }
 
-inline bool isPowerOf2(int64_t C, unsigned &getPow) {
-  if (C < 0) C = -C;
-  if (C > 0 && C == (C & ~(C - 1))) {
-    getPow = log2(static_cast<uint64_t>(C));
-    return true;
+// Log2_32 - This function returns the floor log base 2 of the specified value, -1 if the value is zero.
+// (32 bit edition.)
+// Ex. Log2_32(32) == 5, Log2_32(1) == 0, Log2_32(0) == -1
+inline unsigned Log2_32(unsigned Value) {
+    return 31 - CountLeadingZeros_32(Value);
   }
 
-  return false;
+// Log2_64 - This function returns the floor log base 2 of the specified value, -1 if the value is zero.
+// (64 bit edition.)
+inline unsigned Log2_64(unsigned Value) {
+    return 63 - CountLeadingZeros_64(Value);
 }
 
 // Platform-independent wrappers for the C99 isnan() function.