Re: Limit or Bug?
Date: Sat, 5 Jul 2008 00:46:13 -0700 (PDT)
Message-ID: <737872.4330.qm@web56612.mail.re3.yahoo.com>
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 -- http://www.freelists.org/webpage/oracle-lReceived on Sat Jul 05 2008 - 02:46:13 CDT