diff options
author | lloyd <lloyd@randombit.net> | 2006-05-18 18:33:19 +0000 |
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committer | lloyd <lloyd@randombit.net> | 2006-05-18 18:33:19 +0000 |
commit | a2c99d3270eb73ef2db5704fc54356c6b75096f8 (patch) | |
tree | ad3d6c4fcc8dd0f403f8105598943616246fe172 /src/util.cpp |
Initial checkin1.5.6
Diffstat (limited to 'src/util.cpp')
-rw-r--r-- | src/util.cpp | 81 |
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); + } + +} |