1 files changed, 81 insertions, 0 deletions
diff --git a/src/util.cpp b/src/util.cpp
new file mode 100644
index 000000000..9f6d08a81
--- /dev/null
+++ b/src/util.cpp
@@ -0,0 +1,81 @@
+/*************************************************
+* Utility Functions Source File                  *
+* (C) 1999-2006 The Botan Project                *
+*************************************************/
+
+#include <botan/util.h>
+#include <botan/bit_ops.h>
+#include <algorithm>
+#include <cmath>
+
+namespace Botan {
+
+/*************************************************
+* Round up n to multiple of align_to             *
+*************************************************/
+u32bit round_up(u32bit n, u32bit align_to)
+   {
+   if(n % align_to || n == 0)
+      n += align_to - (n % align_to);
+   return n;
+   }
+
+/*************************************************
+* Round down n to multiple of align_to           *
+*************************************************/
+u32bit round_down(u32bit n, u32bit align_to)
+   {
+   return (n - (n % align_to));
+   }
+
+/*************************************************
+* Return the work required for solving DL        *
+*************************************************/
+u32bit dl_work_factor(u32bit n_bits)
+   {
+   const u32bit MIN_ESTIMATE = 64;
+
+   if(n_bits < 32)
+      return 0;
+
+   const double log_x = n_bits / 1.44;
+
+   u32bit estimate = (u32bit)(2.76 * std::pow(log_x, 1.0/3.0) *
+                                     std::pow(std::log(log_x), 2.0/3.0));
+
+   return std::max(estimate, MIN_ESTIMATE);
+   }
+
+/*************************************************
+* Estimate the entropy of the buffer             *
+*************************************************/
+u32bit entropy_estimate(const byte buffer[], u32bit length)
+   {
+   if(length <= 4)
+      return 0;
+
+   u32bit estimate = 0;
+   byte last = 0, last_delta = 0, last_delta2 = 0;
+
+   for(u32bit j = 0; j != length; ++j)
+      {
+      byte delta = last ^ buffer[j];
+      last = buffer[j];
+
+      byte delta2 = delta ^ last_delta;
+      last_delta = delta;
+
+      byte delta3 = delta2 ^ last_delta2;
+      last_delta2 = delta2;
+
+      byte min_delta = delta;
+      if(min_delta > delta2) min_delta = delta2;
+      if(min_delta > delta3) min_delta = delta3;
+
+      estimate += hamming_weight(min_delta);
+      }
+
+   return (estimate / 2);
+   }
+
+}