Segmentation Errors

[Chris Osborne]

Good day to all,

 I believe that these irritatiing little buggers (segmentation errors) have something to do with memory problems. I have a program, (the one that I was discussing with regards to speed), of which I will attach the source code to the bottom of the program. This program works when we input reasonably small numbers. However we need to test some numbers with a minimum of 2 million digits and by the computer throws a segmentation error when it goes round the loop that increases b the second time (just after bb=b + 1).

 Any ideas or help would be very useful. (Like possibly a better way to import the numbers from the files, or maybe we just need to learn to handle memory stacks).

 Thanks in advance
 Chris

 #include <iostream>
 #include <fstream>
 #include <stdio.h>
 #include <gmpxx.h>
 #include <ctime>


 double diffclock(clock_t clock1,clock_t clock2)
 {
 double diffticks=clock1-clock2;
 double diffms=(diffticks*1000)/CLOCKS_PER_SEC;
 return diffms;
 }

 int main (int argc, char *argv[])
 {
 //set up vars as ints in Z
 mpz_t x, xmax, b, d, sqd, sqdsq, c, ab, bb, bx, b_squared;

 //init vars
 mpz_init(x);
 mpz_init(xmax);
 mpz_init(b);
 mpz_init(d);
 mpz_init(sqd);
 mpz_init(sqdsq);
 mpz_init(c);
 mpz_init(ab);
 mpz_init(bb);
 mpz_init(bx);
 mpz_init(b_squared);

 //FILE *file1 = fopen("min.txt", "rb");
 char *minname = "min.txt";
 std::ifstream minfile(minname);
 char temp0[2000001];
 minfile.getline(temp0, 2000001);
 mpz_set_str (x, temp0, 10);

 char *maxname = "max1.txt";
 std::ifstream maxfile(maxname);
 char temp1[2000010];
 maxfile.getline(temp1, 2000010);
 mpz_set_str (xmax, temp1, 10);

 //setting up x's extrema (string(var, where?, base)
 //mpz_set_str (x, argv[1], 10);
 //mpz_set_str (xmax, argv[2], 10);

 //print Testing from: To:
 gmp_printf ("Testing from: %Zd\n\n", x);
 gmp_printf ("To: %Zd\n\n", xmax);


 //start the timer!
 clock_t begin=clock();
 //create output file
 FILE *file = fopen("output.txt", "w");
 FILE *file1 = fopen("notwork.txt", "w");



 //main sub-routine, While x<=xmax
 for( ;mpz_cmp(x, xmax)<0; mpz_add_ui(x,x,1))

 {

 gmp_printf ("Current x: %Zd\n", x);
 //make sure b and the counter are equal to 0
 mpz_set_ui (b,0);



 do
 {
 //add 1 to b on each loop
 mpz_add_ui (b,b,1); //acheived with for
 //gmp_printf("current b: %Zd\n", b);

 //work up to d=(b+1)²-4(41b²-bx)

 //creation of (b+1)²
 mpz_add_ui(bb,b,1);
 mpz_pow_ui(bb,bb,2);

 //creation of 4(41b²-bx)
 mpz_pow_ui(b_squared,b,2);
 //ab=41b²
 mpz_mul_ui(ab,b_squared,41);
 mpz_clear(b_squared);
 //bx=...b*x!!!!
 mpz_mul(bx,b,x);

 /* Not correctly assembling*
 //assembly using submul (rop=op2*(rop-op1))
 //ab=4(41b²-bx)
 mpz_submul_ui(ab,bx,4); */

 //Let's do it the old-fashioned slow assembly way then ^^
 mpz_sub(ab,ab,bx);
 mpz_mul_ui(ab,ab,4);
 mpz_clear(bx);

 //=> d=bb-ab
 mpz_sub(d,bb,ab);
 mpz_clear(bb);
 mpz_clear(ab);


 // iff d is negative and c is equal to zero (counter unused), this counter shouldn't be needed but is a decent safeguard, then print this value of x to the output file
 //This needs to be before the sqrt you stupid bugger!
 if(mpz_sgn(d)<0)
 {
 gmp_fprintf(file, "%Zd,", x);
 break;
 };
 //check if d is a perfect square
 //calculate d's square root
 mpz_sqrt(sqd,d);
 //db gmp_printf("sqd: %Zd \n\n", sqd);
 //and then sqaure the sqaure root
 mpz_mul(sqdsq,sqd,sqd);


 //check if ((floor(d)^1/2)^2)==d and a conditional sub-routine to break our loop and add 1 to a counter
 if(mpz_cmp(sqdsq,d)==0)
 {
 gmp_fprintf(file1, "%Zd,", x);
 break;
 };


 }while(mpz_sgn(d)>=0);

 }


 clock_t end=clock();
 std::cout << "Time elapsed: " << double(diffclock(end,begin)) << " ms"<< std::endl;

 }