On Mon, Aug 7, 2017 at 6:07 PM, Ashutosh Sharma <ashu.coe...@gmail.com> wrote: > Hi, > .. > In step #1, assuming '*' as an arithmetic operator, the left operand > i.e. 'stats.unused_pages' is of type uint32 whereas the right operand > i.e. 'stats.space_per_page' is of type int32 and arithmetic > conversions of the ANSI C standard states: 'if either operand has type > unsigned int, the other operand is converted to unsigned int' which > means stats.space_per_page would be converted to uint32 and then the > multiplication would be performed. But, if the result of > multiplication is greater than the max value accepted by 32 bits > number, we would get an incorrect result. Hence, it is important to do > proper typecasting of operands before performing any arithmetic > operation. In this case, i would typecast both stats.unused_pages and > stats.space_per_page to uint64 and the > perform multiplication on them. Similar handling needs to be done in > step #2 as well. >
I think even if you have typecasted the first variable, it would have served the purpose. /* Count unused pages as free space. */ - stats.free_space += stats.unused_pages * stats.space_per_page; + stats.free_space += ((uint64) stats.unused_pages * + (uint64) stats.space_per_page); Why an extra parenthesis in above case whereas not in below case? I think the code will look consistent if you follow the same coding practice. I suggest don't use it unless you need it. /* * Total space available for tuples excludes the metapage and the bitmap * pages. */ - total_space = (nblocks - (stats.bitmap_pages + 1)) * stats.space_per_page; + total_space = (uint64) (nblocks - (stats.bitmap_pages + 1)) * + (uint64) stats.space_per_page; -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers