Thread: running through a loop using pointers

Originally Posted by boy

Oh, that was my mistake haha; I was shrinking the code for easy reading on here. My whole code is actually unrooling the loop 16x with 10 parallels.

I switched the int to a double now my code works. But I am running into the problem where my code runs off the end of the array and throws a segmentation fault. I tried adding the two if statements to catch it, but it is still getting the fault, is my if statement wrong?

Code:

 
double *max = malloc(ARRAY_SIZE * sizeof(*max));	
				
do{
	if((max-array) < 1000)
	{
		sum = sum + array[0] + array[1] + array[2] + array[3] + array[ 4] + array[5] + array[6] + array[7] + array[8] + array[9] +  array[10] + array[11] + array[12] + array[13] + array[14] + array[15] ;
		array += 16;
	}
	else if ((max-array) < 30)
	{
		sum = sum + array[0] + array[1] + array[2];
		array += 3;
	}
	else
	{
		sum = sum + array[0] + array[1] + array[2] + array[3] + array[ 4] + array[5] + array[6] + array[7] + array[8] + array[9] +  array[10] + array[11] + array[12] + array[13] + array[14] + array[15] ;  
		sum = sum + array[16] + array[17] + array[18] + array[19] + array[20] + array[21] + array[22] + array[23] + array[24] + array[25] + array[26] + array[27] + array[28] + array[29] + array[30] + array[31]; 
		sum = sum + array[32] + array[33] + array[34] + array[35] + array[36] + array[37] + array[38] + array[39] + array[40] + array[41] + array[42] + array[43] + array[44] + array[45] + array[46] + array[47]; 
		sum = sum + array[48] + array[49] + array[50] + array[51] + array[52] + array[53] + array[54] + array[55] + array[56] + array[57] + array[58] + array[59] + array[60] + array[61] + array[62] + array[63];
		sum = sum + array[64] + array[65] + array[66] + array[67] + array[68] + array[69] + array[70] + array[71] + array[72] + array[73] + array[74] + array[75] + array[76] + array[77] + array[78] + array[79];
		sum = sum + array[80] + array[81] + array[82] + array[83] + array[84] + array[85] + array[86] + array[87] + array[88] + array[89] + array[90] + array[91] + array[92] + array[93] + array[94] + array[95];
		sum = sum + array[96] + array[97] + array[98] + array[99] + array[100] + array[101] + array[102] + array[103] + array[104] + array[105] + array[106] + array[107] + array[108] + array[109] + array[110] + array[111];
		sum = sum + array[112] + array[113] + array[114] + array[115] + array[116] + array[117] + array[118] + array[119] + array[120] + array[121] + array[122] + array[123] + array[124] + array[125] + array[126] + array[127];
		sum = sum + array[128] + array[129] + array[130] + array[131] + array[132] + array[133] + array[134] + array[135] + array[136] + array[137] + array[138] + array[139] + array[140] + array[141] + array[142] + array[143];
		sum = sum + array[144] + array[145] + array[146] + array[147] + array[148] + array[149] + array[150] + array[151] + array[152] + array[153] + array[154] + array[155] + array[156] + array[157] + array[158] + array[159];
										
		array += 160;
		}	
}	
while(array < max);

Dear god man, read up on the use of loops...

You don't have to answer this but... about your C textbook... are you reading it in study fashion or trying to treate it as some kind of reference book for your own version of C... There is only one way to successfully learn C... Take your textbook, open it to page 1, read the words sequentially repeating as necessary, until you understand... Type up the examples and run them, play with the code, make changes, repeat as necessary until you understand... Do the quizzes, work them on your own, figure them out and get the code to work... now turn to page 2... then page 3 and so on until you reach the end of the book... THEN you can try writing code on your own. No offense, but what you got going on is simply not it...

This is my current full code:

Code:

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

// the code you submit must have these two values
#define N_TIMES     600000
#define ARRAY_SIZE   10000

int main (void)
{
    double  *array = calloc(ARRAY_SIZE, sizeof(double));
    double  sum = 0;
    int     i;

    printf("CS201 - Asgmt 4 - Albert Le\n");

    for (i = 0; i < N_TIMES; i++) {

        // do not change anything above this comment,
        // except for your name
				
				int sum0 = 0;
				int sum1 = 0; 
				int sum2 = 0; 
				int sum3 = 0;
				int sum4 = 0;
				int sum5 = 0; 
				int sum6 = 0;
				int sum7 = 0; 
				int sum8 = 0; 
				int sum9 = 0;
				double *end = array +ARRAY_SIZE -160 ;	
				
				do{

							sum0 = sum + array[0] + array[1] + array[2] + array[3] + array[ 4] + array[5] + array[6] + array[7] + array[8] + array[9] +  array[10] + array[11] + array[12] + array[13] + array[14] + array[15] ;  
							sum1 = sum0 + array[16] + array[17] + array[18] + array[19] + array[20] + array[21] + array[22] + array[23] + array[24] + array[25] + array[26] + array[27] + array[28] + array[29] + array[30] + array[31]; 
							sum2 = sum1+ array[32] + array[33] + array[34] + array[35] + array[36] + array[37] + array[38] + array[39] + array[40] + array[41] + array[42] + array[43] + array[44] + array[45] + array[46] + array[47]; 
							sum3 = sum2 + array[48] + array[49] + array[50] + array[51] + array[52] + array[53] + array[54] + array[55] + array[56] + array[57] + array[58] + array[59] + array[60] + array[61] + array[62] + array[63];
							 sum4 = sum3 + array[64] + array[65] + array[66] + array[67] + array[68] + array[69] + array[70] + array[71] + array[72] + array[73] + array[74] + array[75] + array[76] + array[77] + array[78] + array[79];
							sum5 = sum4+ array[80] + array[81] + array[82] + array[83] + array[84] + array[85] + array[86] + array[87] + array[88] + array[89] + array[90] + array[91] + array[92] + array[93] + array[94] + array[95];
							sum6 = sum5 + array[96] + array[97] + array[98] + array[99] + array[100] + array[101] + array[102] + array[103] + array[104] + array[105] + array[106] + array[107] + array[108] + array[109] + array[110] + array[111];
							sum7 = sum6 + array[112] + array[113] + array[114] + array[115] + array[116] + array[117] + array[118] + array[119] + array[120] + array[121] + array[122] + array[123] + array[124] + array[125] + array[126] + array[127];
							sum8 = sum7 + array[128] + array[129] + array[130] + array[131] + array[132] + array[133] + array[134] + array[135] + array[136] + array[137] + array[138] + array[139] + array[140] + array[141] + array[142] + array[143];
							sum9 = sum8 + array[144] + array[145] + array[146] + array[147] + array[148] + array[149] + array[150] + array[151] + array[152] + array[153] + array[154] + array[155] + array[156] + array[157] + array[158] + array[159]; 
							
							sum = sum9;
							
							array = array + 160;
				}	
				while(array < end );
									
				
        // do not change anything below this comment

        }
    return 0;
}

Sorry if I didn't answer this earlier, but my goal for this assignment is to optimize the program that is the reason for all the unrool and splits.

I just went through my debugger several times again and finally found out that my array was not incrementing at all, it was staying at the same start point, I am guessing that is why my code is getting a segmentation fault. I don't know how else I would be able to increment array otherwise, could someone help?

Thanks for your help laserlight, all variables values will be tested as is for the grade. I am actually even allowed to alter the outer loop at all.

I changed all the sums to reuse sum, and change the iterations to be of 100, but I still get a segmentation fault.

Thanks everyone for your help, mission accomplished and submitted.

boy

I just created a new pointer to point to the array

Code:

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

// the code you submit must have these two values
#define N_TIMES     600000
#define ARRAY_SIZE   10000

int main (void)
{
    double  *array = calloc(ARRAY_SIZE, sizeof(double));
    double  sum = 0;
    int     i;

    printf("CS201 - Asgmt 4 - Albert Le\n");

    for (i = 0; i < N_TIMES; i++) {

        // do not change anything above this comment,
        // except for your name
				
				//int j = 0;
				double *a = malloc(sizeof(double));
				a = array;
				double *end = array + ARRAY_SIZE;
				
				for(;a < end; a += 100)
				{
						sum +=  a[0] + a[1] + a[2] + a[3] + a[ 4] + a[5] + a[6] + a[7] + a[8] + a[9] +  a[10] + a[11] + a[12] + a[13] + a[14] + a[15] ;  
						sum +=  a[16] + a[17] + a[18] + a[19] + a[20] + a[21] + a[22] + a[23] + a[24] + a[25] + a[26] + a[27] + a[28] + a[29] + a[30] + a[31]; 
						sum +=  a[32] + a[33] + a[34] + a[35] + a[36] + a[37] + a[38] + a[39] + a[40] + a[41] + a[42] + a[43] + a[44] + a[45] + a[46] + a[47]; 
						sum +=  a[48] + a[49] + a[50] + a[51] + a[52] + a[53] + a[54] + a[55] + a[56] + a[57] + a[58] + a[59] + a[60] + a[61] + a[62] + a[63];
						sum += a[64] + a[65] + a[66] + a[67] + a[68] + a[69] + a[70] + a[71] + a[72] + a[73] + a[74] + a[75] + a[76] + a[77] + a[78] + a[79];
						sum += a[80] + a[81] + a[82] + a[83] + a[84] + a[85] + a[86] + a[87] + a[88] + a[89] + a[90] + a[91] + a[92] + a[93] + a[94] + a[95] + a[96] + a[97] + a[98] + a[99];								
				}
        // do not change anything below this comment

        }
    return 0;
}

What about using another loop for the 100 manual sums ?

Originally Posted by manasij7479

What about using another loop for the 100 manual sums ?

Or boy, since your professor wants pre-emptively optimized code for some reason, it would be funny if you used Duff's device.

Good thing I posted my code on here for you to see laserlight, cut .6 seconds off of my time with just that change, and was able to resubmit it with 3 minutes to spare. Thank you laserlight.
Final time was 5.1 seconds average over 5 runs, which before was 5.65 average.

lol whiteflags, i'm not sure how he would grade me if i implemented that

Anyways, Thanks again for all your guys help, and quick replies