Re: Limit or Bug?

Few more interesting results:

SQL>      select 125 + level sno,
  2              power(2, 125 + level) pow,
  3              (power(2, 125 + level)-1) "pow-1",
  4              mod( power(2, 125 + level)-1, 2) "mod"
  5         from dual
  6         connect BY level <= 25;

       SNO        POW      pow-1        mod
---------- ---------- ---------- ----------
       126 8.5071E+37 8.5071E+37          1
       127 1.7014E+38 1.7014E+38          1
       128 3.4028E+38 3.4028E+38         -1
       129 6.8056E+38 6.8056E+38         -1
       130 1.3611E+39 1.3611E+39         -1
       131 2.7223E+39 2.7223E+39         -1
       132 5.4445E+39 5.4445E+39         -1
       133 1.0889E+40 1.0889E+40          0
       134 2.1778E+40 2.1778E+40          0
       135 4.3556E+40 4.3556E+40          0
       136 8.7112E+40 8.7112E+40       -100
       137 1.7422E+41 1.7422E+41       -100
       138 3.4845E+41 3.4845E+41       -100
       139 6.9690E+41 6.9690E+41       -100
       140 1.3938E+42 1.3938E+42          0
       141 2.7876E+42 2.7876E+42     -10000
       142 5.5752E+42 5.5752E+42          0
       143 1.1150E+43 1.1150E+43     -10000
       144 2.2301E+43 2.2301E+43          0
       145 4.4601E+43 4.4601E+43          0
       146 8.9203E+43 8.9203E+43          0
       147 1.7841E+44 1.7841E+44          0
       148 3.5681E+44 3.5681E+44          0
       149 7.1362E+44 7.1362E+44   -1000000
       150 1.4272E+45 1.4272E+45   -1000000

25 rows selected.

Regards

Asif Momen
http://momendba.blogspot.com

• On Thu, 7/3/08, Charles Schultz <sacrophyte_at_gmail.com> wrote: From: Charles Schultz <sacrophyte_at_gmail.com> Subject: Re: Limit or Bug? To: jkstill_at_gmail.com Cc: "Oracle-L Freelists" <oracle-l_at_freelists.org> Date: Thursday, July 3, 2008, 2:19 PM

Interesting indeed:

SQL > select mod(3.4028E+38,2) from dual;

MOD(3.4028E+38,2)

                0

SQL > select mod(3.4028E+38 + 1,2) from dual;

MOD(3.4028E+38+1,2)

                 -1

On Thu, Jul 3, 2008 at 3:44 PM, Jared Still <jkstill_at_gmail.com> wrote:

The following bit of SQL uses the mod() function to determine modulus 2 of two large numbers

13:37:20 SQL>set echo on
13:37:24 SQL>@mod_test
13:37:25 SQL>
13:37:25 SQL>
13:37:25 SQL>

13:37:25 SQL>select mod(power(2,127)-1,2) from dual 13:37:25   2  /

MOD(POWER(2,127)-1,2)

                    1

1 row selected.

13:37:25 SQL>
13:37:25 SQL>select mod(power(2,128)-1,2) from dual

13:37:25   2  /

MOD(POWER(2,128)-1,2)

                   -1

1 row selected.

13:37:25 SQL>

Notice that mod(power(2,128)-1,2) returns an incorrect answer, while the

answer for mod(power(2,127)-1,2) is correct.

Does someone here know why?

Is it a limit?

Or is it a bug?

Please supply an explanation and/or URL for your answer.  :)

My guess (yes Alex, it's a guess, or rather, a hunch) is that this is

related to two's complement binary numbers, but I haven't been able to (yet) find any explanation for this.

-- 
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist





-- 
Charles Schultz



      
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