array inside array for bit wise operation in Various String Opt Algo's

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what is the meaning of 'S[x[i]]' in the following algorithm program, i understand how '&','<<' and all other code of program, but not sure about 'S[x[i]]', because in it x[i] clearly does not refer to a index position for array S, because it would not make sense as in my example, x[0] = 97/'a' and my S array has a size limit of max 32.

C++

int preSo(char *x, int m, unsigned int *S) { 
    unsigned int j, lim; 
    int i; 
    for (i = 0; i < ASIZE; ++i) 
      S[i] = ~0; 
    for (lim = i = 0, j = 1; i < m; ++i, j <<= 1) { 
      S[x[i]] &= ~j; 
      lim |= j; 
    } 
    lim = ~(lim>>1); 
    return(lim); 
  } 

void SO(char *x, int m, char *y, int n) { 
    unsigned int lim, state; 
    unsigned int S[ASIZE]; 
    int j; 
   /* if (m > WORD) 
      error("SO: Use pattern size <= word size"); */

    /* Preprocessing */ 
    lim = preSo(x, m, S); 

    /* Searching */ 
    for (state = ~0, j = 0; j < n; ++j) { 
      state = (state<<1) | S[y[j]]; 
      if (state < lim) 
        OUTPUT(j - m + 1); 
    } 
  } 

void OUTPUT(int n)
{
	printf("%d",n);
}

void main()
{
	char * pattern="abg";
	char * text ="abg and ade ac are not same as ad";
	SO(pattern,3,text,28);
	getch();

}

i am now adding my test result for value of S[x[0]], x[0] = 97 ,S[x[0]] = 3435973836, value of S[97] = 3341248 where is this value coming from.

Posted 1-Jun-15 19:55pm

RajneeshSaysHello

Updated 1-Jun-15 20:29pm

barneyman

v3

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Comments

barneyman 2-Jun-15 2:03am

you're correct - it means the S[97] (where 97 is gleaned from x[0])

RajneeshSaysHello 2-Jun-15 2:27am

please see test results

barneyman 2-Jun-15 2:38am

there's nothing special about the code S[x[0]] - it's original value is 0xCCCCCCCC (which is stack 'undefined' value in debug) - i don't know where you're getting 0x32FBC0 from

S is initialised to -1 in preSo, and then there's some XORing going on ...

Debug it ...

RajneeshSaysHello 2-Jun-15 2:57am

i did and showed different value's of S[..] with xor and without xor.

Sergey Alexandrovich Kryukov 2-Jun-15 2:06am

There is nothing worse than trying to explain how something work in a program that you did not write and I would never try to write. This is just a waste of time. Start writing your own code; then we will gladly help you.
—SA

_Asif_ 2-Jun-15 3:43am

couldn't agree more

RajneeshSaysHello 2-Jun-15 2:26am

please see my test result now, as i have not defined any value of S[97] anywhere in my code.

RajneeshSaysHello 2-Jun-15 3:09am

also i am not just trying to understand this code, i am asking for the particular variable value.

Mohibur Rashid 2-Jun-15 3:32am

You will have to go a long way to understand this. 97 is the ascii value of 'a' and you are saying haven't defined S[97]. As other suggested you need to learn how to debug.

in simple S[x[i]] == S[97] when i==0, s[0] is 'a'; and 97 is the number.

RajneeshSaysHello 2-Jun-15 3:54am

i have posted my debug result i will post here again:
S[ASize];//declaring it ASIZE is 26(no of alphabets) got it, ok
x[0] = 'a', x[1] = 'b', x[2] = 'g'//got it simple, ok moving on
S[0] = ~0 //~0 is 2 times 32 and is some huge value
....
...
S[32] = ~0// same as S[0]

now i have not defined S[97] or S[x[0]] so i do not know where it value is defined or it is getting from, i can easily take the logic and build my own without using this code, but i need to understand a "C" language value assignment in this particular case , forget whole code it is here just to show you an example where such a case is happening,

Mohibur Rashid 2-Jun-15 4:01am

What compiler are you using? you are calling getch() function. If you are using tc3.0, it will not give you any error.

RajneeshSaysHello 2-Jun-15 4:06am

its mvs2010

RajneeshSaysHello 2-Jun-15 4:06am

why should i get an error ? because i am fetching value of S[97] when it is not defined, hmm,, i am thinking it is somehow related to being an unsigned int

Stefan_Lang 2-Jun-15 8:52am

You're right. it doesn't make sense. The code is wrong, whatever it is trying to achieve.

The values you'll get will depend on the current state of your system, your compiler, and potentially the flags and settings used to build the program, so it is no wonder you don't get the same results as others: S[x[i]] is undefined, and that you don't get the same results is exactly what undefined means!

[no name] 30-Jan-23 2:55am

In main function:
char * pattern="abg";

call to SO function in main:
SO(pattern,3,text,28);

entering SO function:
SO(char *x, int m, char *y, int n)

&pattern is now first parameter to SO function, &x

from SO function:
lim = preSo(x, m, S);

&pattern now going to preSo as first parameter x

in preSo function:
S[x[i]] &= ~j;

brackets have highest precedence so x[i] is evaluated first an x is a ptr to
pattern and pattern[0] is 'a' ascii 97 decimal...

I think thats what is happening?

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