Databases
StackOverflow2013
Postsdbo
POVerify if a binary array is a subset of another one in C
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POVerify if a binary array is a subset of another one in C
    primarykey
    data
    text
    <p>I need to verify if the bits in an array of bytes (i.e. chars) are a subset of another array of the same type: for example, 0001.0011 (19) is a subset of 0011.0011 (51), while 0000.1011 (11) is not.</p> <p>I started playing with bitwise operations, and almost solved it with a XOR/OR/XOR sequence:</p> <pre><code>int is_subset (char *set_a, char *set_b, int size) { /* The operation is performed with three bitwise operations, resulting in a * sequence of bits that will be equal to zero if set_a is a subset of * set_b. As a bonus, the positions where the sets differ will be * available in the resulting sequence, and thus the number of differing * positions can be obtained by counting the number of bits set (for exemple, * with __builtin_popcount in GCC). * * Exemple (TRUE): Exemple (FALSE): * ================ ================ * set_a 00010011 set_a 00001011 * set_b 00110011 set_b 00110011 * ---------------- ---------------- * XOR 00100000 XOR 00111000 * set_b 00110011 set_b 00110011 * ---------------- ---------------- * OR 00110011 OR 00111011 * set_b 00110011 set_b 00110011 * ---------------- ---------------- * XOR 00000000 XOR 00001000 */ int i; for (i = 0; i &lt; size; i++) if ( (((set_a[i] ^ set_b[i]) | set_b[i]) ^ set_b[i]) != 0) return FALSE; return TRUE; } </code></pre> <p>but it fails (always returning TRUE) if <code>set_a</code> is zero (0000.0000). I tried different strategies (such as Bloom filters), but probably due to my programming skills it was far from fast or at least elegant.</p> <p>Is there any standard, elegant way of doing this without exceptions?</p> <p>EDIT: to be clear, in this context "subset" means that all bits TRUE in the first array (set_a) are also TRUE in the second one (set_b). There might be other bits TRUE in the second array, but it does not matter if they are FALSE in first array.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USGiacomo
    1. USGiacomo
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. USHatch
      1. VTFavorite
    1. COPerhaps I'm missing something in the question, but what is your definition of a subset in this context?
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. USCorbin
    2. COSorry, edited the question!
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. USGiacomo
    3. COIf your definition of a subset is what you appear to think it is, (judging by your code,) then you should not be bothering us with arrays, and you could just be asking us how to figure out whether the '1' bits of an int are a subset of the '1' bits of another int.
      singulars
      1. POVerify if a binary array is a subset of another one in C
      1. USMike Nakis
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload