#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

int highbit (uint32_t n)
{
   assert (n != 0);

   int  result = 0;
   if (n & 0xFFFF0000) {
      result  += 16;
      n      >>= 16;
   }
   if (n & 0xFF00) {
      result  += 8;
      n      >>= 8;
   }
   if (n & 0xF0) {
      result  += 4;
      n      >>= 4;
   }
   if (n & 0xC) {
      result  += 2;
      n      >>= 2;
   }
   if (n & 0x2) {
      result  += 1;
      n      >>= 1;
   }
   return result;
}

inline uint32_t min (uint32_t a, uint32_t b)
{
   return (a<b) ? a : b;
}

uint32_t maxOr (uint32_t    minA, uint32_t minB,
                uint32_t    maxA, uint32_t maxB)
{
   assert (minA <= maxA);
   assert (minB <= maxB);

   if (maxA == 0) return maxB;
   if (maxB == 0) return maxA;

   uint32_t a = maxA ^ minA;
   if (a != 0)
      a = ((1 << highbit (a)) - 1);

   uint32_t b = maxB ^ minB;
   if (b != 0)
      b = ((1 << highbit (b)) - 1);

   uint32_t  t = maxA & maxB;
   if (t != 0)
      t = ((1 << highbit (t)) - 1);

   return min (maxA|maxB|a|b, maxA|maxB|t);
}

int main (int, char**)
{
   uint32_t minA = 200;
   uint32_t maxA = 783;
   uint32_t minB = 69;
   uint32_t maxB = 609;
   printf ("minA=%x\n"
           "maxA=%x\n"
           "minB=%x\n"
           "maxB=%x\n"
           "maxOr=%x\n",
           minA, maxA, minB, maxB,
           maxOr (minA, minB, maxA, maxB));
   return 0;
}