1 files changed, 103 insertions, 0 deletions
diff --git a/src/lib/utils/bit_ops.h b/src/lib/utils/bit_ops.h
new file mode 100644
index 000000000..0072fde71
--- /dev/null
+++ b/src/lib/utils/bit_ops.h
@@ -0,0 +1,103 @@
+/*
+* Bit/Word Operations
+* (C) 1999-2008 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_BIT_OPS_H__
+#define BOTAN_BIT_OPS_H__
+
+#include <botan/types.h>
+
+namespace Botan {
+
+/**
+* Power of 2 test. T should be an unsigned integer type
+* @param arg an integer value
+* @return true iff arg is 2^n for some n > 0
+*/
+template<typename T>
+inline bool is_power_of_2(T arg)
+   {
+   return ((arg != 0 && arg != 1) && ((arg & (arg-1)) == 0));
+   }
+
+/**
+* Return the index of the highest set bit
+* T is an unsigned integer type
+* @param n an integer value
+* @return index of the highest set bit in n
+*/
+template<typename T>
+inline size_t high_bit(T n)
+   {
+   for(size_t i = 8*sizeof(T); i > 0; --i)
+      if((n >> (i - 1)) & 0x01)
+         return i;
+   return 0;
+   }
+
+/**
+* Return the index of the lowest set bit
+* T is an unsigned integer type
+* @param n an integer value
+* @return index of the lowest set bit in n
+*/
+template<typename T>
+inline size_t low_bit(T n)
+   {
+   for(size_t i = 0; i != 8*sizeof(T); ++i)
+      if((n >> i) & 0x01)
+         return (i + 1);
+   return 0;
+   }
+
+/**
+* Return the number of significant bytes in n
+* @param n an integer value
+* @return number of significant bytes in n
+*/
+template<typename T>
+inline size_t significant_bytes(T n)
+   {
+   for(size_t i = 0; i != sizeof(T); ++i)
+      if(get_byte(i, n))
+         return sizeof(T)-i;
+   return 0;
+   }
+
+/**
+* Compute Hamming weights
+* @param n an integer value
+* @return number of bits in n set to 1
+*/
+template<typename T>
+inline size_t hamming_weight(T n)
+   {
+   const byte NIBBLE_WEIGHTS[] = {
+      0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };
+
+   size_t weight = 0;
+   for(size_t i = 0; i != 2*sizeof(T); ++i)
+      weight += NIBBLE_WEIGHTS[(n >> (4*i)) & 0x0F];
+   return weight;
+   }
+
+/**
+* Count the trailing zero bits in n
+* @param n an integer value
+* @return maximum x st 2^x divides n
+*/
+template<typename T>
+inline size_t ctz(T n)
+   {
+   for(size_t i = 0; i != 8*sizeof(T); ++i)
+      if((n >> i) & 0x01)
+         return i;
+   return 8*sizeof(T);
+   }
+
+}
+
+#endif