C++ Program to Implement Segmented Sieve

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This C++ Program demonstrates the implementation of Segmented Sieve.

Here is source code of the C++ Program to demonstrate the implementation of Segmented Sieve. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

  1. /* 
  2.  * C++ Program to Implement Segmented Sieve
  3.  */
  4. #include <iostream>
  5. #include <cstring>
  6. #define MAX 46656
  7. #define LMT 216
  8. #define LEN 4830
  9. #define RNG 100032
  10. #define sq(x) ((x)*(x))
  11. #define mset(x,v) memset(x, v , sizeof(x))
  12. #define chkC(x,n) (x[n >> 6] & (1 << ((n >> 1) & 31)))
  13. #define setC(x,n) (x[n >> 6] |= (1 << ((n >> 1) & 31)))
  14. using namespace std;
  15. unsigned base[MAX/64], segment[RNG/64], primes[LEN];
  16.  
  17. /* 
  18.  * Generates all the necessary prime numbers and marks them in base[]
  19.  */
  20. void sieve()
  21. {
  22.     unsigned i, j, k;
  23.     for (i = 3; i < LMT; i += 2)
  24.     {
  25.         if (!chkC(base, i))
  26.         {    
  27.             for (j = i * i, k = i << 1; j < MAX; j += k)
  28.                 setC(base, j);
  29.         }
  30.     }
  31.     for (i = 3, j = 0; i < MAX; i += 2)
  32.     {
  33.         if (!chkC(base, i))
  34.             primes[j++] = i;
  35.     }
  36. }
  37.  
  38. /*
  39.  * Returns the prime-count within range [a,b] and marks them in segment[] 
  40.  */
  41. int segmented_sieve(int a, int b)
  42. {
  43.     unsigned i, j, k, cnt = (a <= 2 && 2 <=b )? 1 : 0;
  44.     if (b < 2) 
  45.         return 0;
  46.     if (a < 3) 
  47.         a = 3;
  48.     if (a % 2 == 0) 
  49.         a++;
  50.     mset (segment, 0);
  51.     for (i = 0; sq(primes[i]) <= b; i++)
  52.     {
  53.         j = primes[i] * ((a + primes[i] - 1) / primes[i]);
  54.         if (j % 2 == 0) j += primes[i];
  55.         for (k = primes[i] << 1; j <= b; j += k)
  56.         {
  57.             if (j != primes[i])
  58.                 setC(segment, (j - a));
  59.         }
  60.     }
  61.     for (i = 0; i <= b - a; i += 2)
  62.     {
  63.         if (!chkC(segment, i))
  64.             cnt++;
  65.     }
  66.     return cnt;
  67. }
  68. /* 
  69.  * Main
  70.  */
  71. int main()
  72. {
  73.     sieve();
  74.     int a, b;
  75.     cout<<"Enter Lower Bound: ";
  76.     cin>>a;
  77.     cout<<"Enter Upper Bound: ";
  78.     cin>>b;
  79.     cout<<"Number of primes between "<<a<<" and "<<b<<":  ";
  80.     cout<<segmented_sieve(a, b)<<endl;
  81.     return 0;
  82. }

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$ g++ sieve_segemented.cpp
$ a.out
 
Enter Lower Bound: 7
Enter Upper Bound: 600
Number of primes between 7 and 600:  106
 
------------------
(program exited with code: 1)
Press return to continue

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn