/*
* (C) 2021 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/rfc4880.h>
#include <algorithm>

namespace Botan {

namespace {

/*
PGP stores the iteration count as a single byte
Thus it can only actually take on one of 256 values, based on the
formula in RFC 4880 section 3.6.1.3
*/
static const uint32_t OPENPGP_S2K_ITERS[256] = {
   1024, 1088, 1152, 1216, 1280, 1344, 1408, 1472, 1536, 1600,
   1664, 1728, 1792, 1856, 1920, 1984, 2048, 2176, 2304, 2432,
   2560, 2688, 2816, 2944, 3072, 3200, 3328, 3456, 3584, 3712,
   3840, 3968, 4096, 4352, 4608, 4864, 5120, 5376, 5632, 5888,
   6144, 6400, 6656, 6912, 7168, 7424, 7680, 7936, 8192, 8704,
   9216, 9728, 10240, 10752, 11264, 11776, 12288, 12800, 13312,
   13824, 14336, 14848, 15360, 15872, 16384, 17408, 18432, 19456,
   20480, 21504, 22528, 23552, 24576, 25600, 26624, 27648, 28672,
   29696, 30720, 31744, 32768, 34816, 36864, 38912, 40960, 43008,
   45056, 47104, 49152, 51200, 53248, 55296, 57344, 59392, 61440,
   63488, 65536, 69632, 73728, 77824, 81920, 86016, 90112, 94208,
   98304, 102400, 106496, 110592, 114688, 118784, 122880, 126976,
   131072, 139264, 147456, 155648, 163840, 172032, 180224, 188416,
   196608, 204800, 212992, 221184, 229376, 237568, 245760, 253952,
   262144, 278528, 294912, 311296, 327680, 344064, 360448, 376832,
   393216, 409600, 425984, 442368, 458752, 475136, 491520, 507904,
   524288, 557056, 589824, 622592, 655360, 688128, 720896, 753664,
   786432, 819200, 851968, 884736, 917504, 950272, 983040, 1015808,
   1048576, 1114112, 1179648, 1245184, 1310720, 1376256, 1441792,
   1507328, 1572864, 1638400, 1703936, 1769472, 1835008, 1900544,
   1966080, 2031616, 2097152, 2228224, 2359296, 2490368, 2621440,
   2752512, 2883584, 3014656, 3145728, 3276800, 3407872, 3538944,
   3670016, 3801088, 3932160, 4063232, 4194304, 4456448, 4718592,
   4980736, 5242880, 5505024, 5767168, 6029312, 6291456, 6553600,
   6815744, 7077888, 7340032, 7602176, 7864320, 8126464, 8388608,
   8912896, 9437184, 9961472, 10485760, 11010048, 11534336,
   12058624, 12582912, 13107200, 13631488, 14155776, 14680064,
   15204352, 15728640, 16252928, 16777216, 17825792, 18874368,
   19922944, 20971520, 22020096, 23068672, 24117248, 25165824,
   26214400, 27262976, 28311552, 29360128, 30408704, 31457280,
   32505856, 33554432, 35651584, 37748736, 39845888, 41943040,
   44040192, 46137344, 48234496, 50331648, 52428800, 54525952,
   56623104, 58720256, 60817408, 62914560, 65011712 };

}

uint8_t RFC4880_encode_count(size_t desired_iterations)
   {
   if(desired_iterations <= OPENPGP_S2K_ITERS[0])
      return 0;

   if(desired_iterations >= OPENPGP_S2K_ITERS[255])
      return 255;

   auto i = std::lower_bound(OPENPGP_S2K_ITERS, OPENPGP_S2K_ITERS + 256, desired_iterations);

   return static_cast<uint8_t>(i - OPENPGP_S2K_ITERS);
   }

size_t RFC4880_decode_count(uint8_t iter)
   {
   return OPENPGP_S2K_ITERS[iter];
   }

}