gistfile1.cpp

#include <stdio.h>
#include <bitset>
#include <iostream>
#include <map>
#include <cstring>
#include <string>

using namespace std;

int bitCount(unsigned int num) {
  bitset<32> set(num);
  int count = 32;
  for (int i = 1; i <= 32; ++i) {
    if (set[32 - i]) break;
    --count;
  }
  return count;
}

unsigned int reverseXor(unsigned int num) {
  bitset<32> orig(num), mod(num>>6), res(num);
  int blank = 32 - bitCount(num>>6);
  int i;
  for (i = 31; i > 32 - (blank + 6) && i > 0; --i)
    orig.set(i, res[i] ^ mod[i]);
  for (; i >= 0; --i) {
    mod.set(i, orig[i + 6]);
    orig.set(i, res[i] ^ mod[i]);
  }
  return (unsigned int)orig.to_ulong();
}

int hash(const char* str, int l, int h = 0) {
  for (int i = 0; i < l; ++i) {
    h += (int)*(str + i);
    h += (h << 10);
    h ^= (h >> 6);
  }
  return h;
}

int hashback(const char* str, int l, int target) {
  unsigned int h = target;
  for (; l > 0; --l) {
    h = reverseXor(h);
    h = h * [REDACTED];
    h -= (int)*(str + l - 1);
  }
  return h;
}

int permuteChar(char* c) {
  *c += 1;
  if (*c == 91) *c = 97;
  else if (*c == 123) {
    *c = 65;
    return 1;
  }
  return 0;
}

bool permute(char* str, int len) {
  for (int i = len - 1; i >= 0; --i) {
    if (!permuteChar(str + i)) return true;
  }
  return false;
}

int main(int argc, char** argv) {
  map<int, string> precomp;
  int target = 55555;
  char* prefix = new char[4];
  strcpy(prefix, "AAA");
  do {
    precomp[hashback(prefix, 3, target)] = string(prefix);
  } while (permute(prefix, 3));
  char* str = new char[8];
  str[7] = 0;
  if (argc > 1) strncpy(str, argv[1], 6);
  else strcpy(str, "AAAAAAA");
  do {
    int h = hash(str, 7);
    map<int, string>::iterator hit = precomp.find(h);
    if (hit != precomp.end() && hash((string(str) + hit->second).c_str(), 10) == target) {
      cout << str << hit->second << endl;
    }
  } while (permute(str, 7));
  return 0;
}