Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Your method does not work for several reasons:</p> <ul> <li><p>Assuming <code>x</code> and <code>y</code> are signed values, the subtraction could overflow. Not only does this result in <em>undefined behavior</em> according to the C standard, but on typical implementations where overflow wraps, it will give the wrong results. For instance, if <code>x</code> is <code>INT_MIN</code> and <code>y</code> is <code>1</code>, <code>x-y</code> will yield <code>INT_MAX</code>, which does not have its high bit set.</p></li> <li><p>If <code>x</code> and <code>y</code> are unsigned values, then <code>x=UINT_MAX</code> and <code>y=0</code> is an example where you get the wrong answer. You'd have to impose a condition on the values of <code>x</code> and <code>y</code> (for instance, that neither has its high bit set) in order for this test to work.</p></li> </ul> <p>What it comes down to is that in order to perform comparisons by testing the "high bit", you need one more bit than the number of bits in the values being compared. In assembly language on reasonably-CISC-ish architectures, the carry flag provides this extra bit, and special conditional jump instructions (as well as carry/borrow instructions) are able to read the value of the carry flag. C provides no way to access such a carry flag, however. One alternate approach might be to use a larger integer type (like <code>long long</code>) so that you can get an extra bit in your result. Good compilers will translate this to a read of the carry flag, rather than actually performing larger arithmetic operations.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow to compare two numbers to see which is greater
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USR..
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHow to compare two numbers to see which is greater
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COi forgot to mention I am working on 2's complement. I'm working with a lot of restriction on this. I can only use ints. If I can check there is a overflow, is there another way to check that the x>y?
      singulars
      1. PO
      1. USDan
    2. COInteger overflow does *not* result in undefined behaviour. The behaviour of integer over-/underflows is well-defined for each host platform.
      singulars
      1. PO
      1. USDevSolar
    3. CO@DevSolar, I think R is correct. See [CERT](https://www.securecoding.cert.org/confluence/display/seccode/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow) and §6.5/5 of C99. Of course, *unsigned* overflow is guaranteed to wrap.
      singulars
      1. PO
      1. USMatthew Flaschen
 

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