DevCPP generated binary is getting hung.

[Abhinandan H Patil]

Hi DevCPP team,

You are doing great job.. Keep going..

Here is the issue which you may want to have a look at.

I am generating 100,000 random numbers using built in function and using the
customised function.

I expect the time to do so is linear function of input size.However the
generated binary works for 10,000 numbers but not for 100,000 numbers.

Here is the code which you may want to execute..

include <stdio.h>

include <stdlib.h>

//#include <sys times.h="">

define NO_OF_RANDOM_NOS 100000

int randCustom(int seed); / Function prototype /
/ Variables for the program/
int randomNumberArray,iter,iter1,dupValue=0,dupValueBuiltIn=0;
int builtInRandomNumberArray,dupFlag,dupBuiltInFlag;
long customStart,customEnd,builtInStart,builtInEnd;
//struct tms
structCustomStart,structCustomEnd,structBuiltInStart,structBuiltInEnd;
int main()
{
/ srand ( time(NULL) ); /
//customStart = times (&structCustomStart);
for(iter=0;iter<=NO_OF_RANDOM_NOS;iter++)
{
randomNumberArray=randCustom(NO_OF_RANDOM_NOSiter+1);
/ Uncomment the following value to see the behaviour for lower
value of seeds
randomNumberArray=randCustom(iter); */
}
//customEnd = times (&structCustomEnd);
printf("\n Custom number generation time = %ld",customEnd -
customStart);
//builtInStart = times(&structBuiltInStart);

for(iter=0;iter<=NO_OF_RANDOM_NOS;iter++)
{
builtInRandomNumberArray=rand();
}
//builtInEnd = times(&structBuiltInEnd);
printf("\n built in number generation time = %ld",builtInEnd -
builtInStart);
for(iter=0;iter<NO_OF_RANDOM_NOS;iter++)
{
for(iter1=0;iter1<NO_OF_RANDOM_NOS;iter1++)
{
if(iter == iter1) continue;
if(randomNumberArray == randomNumberArray)
{
dupFlag = 1;
}
if(builtInRandomNumberArray
==builtInRandomNumberArray)
{
dupBuiltInFlag=1;
}
}
}
dupValue=0;
dupValueBuiltIn=0;
for(iter=0;iter<NO_OF_RANDOM_NOS;iter++)
{
/ printf("The dup indicating flag %d",dupFlag); /
if(dupFlag==1) dupValue++;
if(dupBuiltInFlag==1) dupValueBuiltIn++;
}
printf("The number of duplicates in the custom array %d\n",dupValue);
printf("The number of duplicates in the built in array %d\n",dupValueBuiltIn);
return 0;
}
int randCustom(int seed)
{
static long temp = 100001;
if ( seed == 0 ) return 1;
temp = (temp*125)%2796203;
return ((temp%seed)+1);
}

[Aris]

Lets think about it

randomNumberArray = randCustom(NO_OF_RANDOM_NOS*iter+1);

The seed of randCustom is the value of NO_OF_RANDOM_NOS*iter+1

Values:
NO_OF_RANDOM_NOS: 100.000
iter: 0 to 100000
and the 1 value. Lets calculate it if iter is 99.997

NO_OF_RANDOM_NOS * iter +1 -> 100.000 * 99.997 + 1 -> 9.999.700.000 + 1 ->
9.999.700.001

But seed of randCustom function is int
Is it possible an int variable to store 9.999.700.001???

Usually in 32bit system the size of an int variable is 4bytes.

4bytes or 4 * 8 bits -> 32bits.

the max number that an int (32bits) can store is 2^32 if int is unsigned .

2^32 = 4.294.967.295 < 9.999.700.001 So we have a problem here. int cannot
store the value!!!

But you use int and not unsigned int and thethe max number that an unsigned
int can store is

2^31 -1 = 2.147.483.647 < 9.999.700.001

[Aris]

sorry i made a mistake:
(line: 13)

the max number that an int (32bits) can store is 2^32 - 1 if int is unsigned

2^32 = 4.294.967.295 < 9.999.700.001

[Abhinandan H Patil]

Thanks Arism...

The max value for

The seed of randCustom is the value of NO_OF_RANDOM_NOSiter+1 is
100000100000+1 ~ 10^10 which is far greater than 2^32.However the value
should get truncated and depending upon the compiler "some" value should get
assigned.

Add this line in the beginning :
int junk = 10000000000; and print it.Its get printed as "The value of junk is
1410065408".

I mean to say some value should get assigned.

Here the issue is compiler generated code going into infinite loop.Can some
one check that !!