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authorlloyd <lloyd@randombit.net>2006-05-18 18:33:19 +0000
committerlloyd <lloyd@randombit.net>2006-05-18 18:33:19 +0000
commita2c99d3270eb73ef2db5704fc54356c6b75096f8 (patch)
treead3d6c4fcc8dd0f403f8105598943616246fe172 /src/util.cpp
Initial checkin1.5.6
Diffstat (limited to 'src/util.cpp')
-rw-r--r--src/util.cpp81
1 files changed, 81 insertions, 0 deletions
diff --git a/src/util.cpp b/src/util.cpp
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+/*************************************************
+* 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);
+ }
+
+}