int4, int8, real ....division... - Mailing list pgsql-bugs

pgsql-7.4.2

I think it's not a bug, just interesting results:

SELECT   9223372036854775807/(365*10000000)  ;
result: -14300526699
wrong

SELECT   ( 9223372036854775807/365 )/10000000  ;
result: 2526951242
good

SELECT   ( 9223372036854775807::real /(365*10000000) )  ;
result: -14300526699,6589
wrong

SELECT   ( 9223372036854775807 /(365*10000000)::real )  ;
result: -14300526699,6589
wrong

SELECT   ( 9223372036854775807 /(365*10000000)::real )  ;
result: -14300526699,6589
wrong

SELECT   ( 9223372036854775807/(365*10000000::real) )  ;
result:  2526951242,97391
good

SELECT   ( 9223372036854775807/(365::real*10000000) )  ;
result:  2526951242,97391
good



REASON IS:

SELECT 365*10000000 ;
result: -644967296
wrong

but

SELECT 365*10000000::int8 ;
result: 3650000000
good



If this operation embended in complex expression,
then very difficult to find the reason of computation error.
This misstake comes only after the border of int4 and int8.


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Gyenese Pál Attila
számítástechnikai vezető
MEDIAGNOST KFT.
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