Reconstruction of the `date2drp2` algorithm found in the "VOCALOID5 Libraries Installer", bundled with VOCALOID5 ESV for macOS by SilverFox (https://4download.net/209-yamaha-vocaloid-full-version.html)

date2drp2.c

#include <stdio.h>
#include <string.h>

const char *shifttable = "23456789ABCDEFGHKLMNPRSTWXYZ";

const char *convtable[] = {
  "BELKCFHDGA27SZT8M9W43N6XR5YP",
  "ABCDEFGHKLMNPRSTWXYZ23456789",
  "E8AF2B93D46K7H5CGYPNWZRTLXMS",
  "BK5C6HD2A7F43E89LZGYMNXRWPST",
  "23456789ABCDEFGHKLMNPRSTWXYZ",
  "T7S4WZBYRPXNMF8L9AD2EKCH5G63",
  "9H5KGYXL4MBWA3DC2NZFPERT6S78",
  "XWKTLHRSBMA2DCY3ZNPG865F47E9",
  "AD2EKCH5G6",
  "G6DP9R4SHN",
  "M2DHE7A8KW",
  "FS2NGC6PK9",
  "M7EBX3CYGZ",
  "AT5W8BDH4P",
};

const int tab1[][13] = {
  {8,1,7,5,2,1,7,5,2,1,7,5,2},
  {1,8,2,9,3,8,2,9,3,8,2,9,3},
  {8,6,6,1,8,6,6,1,8,6,6,1,8},
  {6,9,2,7,3,9,2,7,3,9,2,7,3},
  {9,1,8,2,6,1,8,2,6,1,8,2,6},
  {1,1,3,2,7,1,3,2,7,1,3,2,7},
  {1,7,3,4,9,7,3,4,9,7,3,4,9},
  {7,8,2,1,4,8,2,1,4,8,2,1,4},
  {8,6,8,7,8,6,8,7,8,6,8,7,8},
  {6,3,8,7,5,3,8,7,5,3,8,7,5},
  {3,2,4,3,2,2,4,3,2,2,4,3,2},
  {2,7,5,9,1,7,5,9,1,7,5,9,1},
  {7,8,4,6,9,8,4,6,9,8,4,6,9},
  {8,3,6,4,2,3,6,4,2,3,6,4,2},
  {3,9,7,0,7,9,7,0,7,9,7,0,7},
  {9,2,4,1,8,2,4,1,8,2,4,1,8},
};
const int tab2[][13] = {
  {0,1,8,8,7,1,8,8,7,1,8,8,7},
  {1,2,3,0,4,2,3,0,4,2,3,0,4},
  {2,1,5,0,8,1,5,0,8,1,5,0,8},
  {1,0,1,0,1,0,1,0,1,0,1,0,1},
  {0,1,1,0,2,1,1,0,2,1,1,0,2},
  {1,2,9,0,4,2,9,0,4,2,9,0,4},
  {2,5,0,3,0,5,0,3,0,5,0,3,0},
  {5,0,5,0,5,0,5,0,5,0,5,0,5},
  {0,7,0,2,1,7,0,2,1,7,0,2,1},
  {7,9,0,1,5,9,0,1,5,9,0,1,5},
  {9,0,1,1,0,0,1,1,0,0,1,1,0},
  {0,1,1,0,3,1,1,0,3,1,1,0,3},
  {1,2,3,1,1,2,3,1,1,2,3,1,1},
  {2,1,2,2,3,1,2,2,3,1,2,2,3},
  {1,9,1,2,8,9,1,2,8,9,1,2,8},
  {9,8,0,1,9,8,0,1,9,8,0,1,9},
};

static inline int hex2i(char c)
{
  if (c == 'K') return 0;
  if (c == 'L') return 1;
  return (c <= '9' ? c - '0' : c - 'A' + 10);
}
static inline int hex2pos(char c)
{
  for (int i = 0; i < 28; i++) if (shifttable[i] == c) return i;
  return -1;
}
static inline char i2hex(int x)
{
  return (x <= 9 ? x + '0' : x - 10 + 'A');
}

int8_t DecodeID(const char *s, char *t)
{
  if (strlen(s) != 16) return 0;
  memcpy(t, s, 14);
  const int *t1 = tab1[hex2i(s[15])];
  const int *t2 = tab2[hex2i(s[14])];
  for (int i = 1; i < 14; i++) t[i] = shifttable[(hex2pos(t[i]) - t1[i] + 28) % 28];
  for (int i = 1; i < 14; i++) t[i] = shifttable[(hex2pos(t[i]) - t2[i] + 28) % 28];
  for (int i = 0; i < 14; i++) {
    char *p = strchr(convtable[i], t[i]);
    if (p != NULL) t[i] = i2hex(p - convtable[i]);
  }
  return 1;
}

int main()
{
  char t[16] = { 0 };
  DecodeID("BXENFF42PWRK4XE7", t); puts(t); // 005114I0040000
  DecodeID("BXENFF42PWRK4XE8", t); puts(t); // 02E3P7MH9B498C
}