On 06/13/2014 03:57 PM, Åke Forslund wrote: > On fre, 2014-06-13 at 15:33 +0100, Andrew Haley wrote: >> On 06/13/2014 07:42 AM, Sandeep Kumar Singh wrote: >> >>> I need some help/clarification, >>> I am expecting zero value of 16-bit signed value 0x8000 after left shift by 2 >> >> It's undefined. > > A small side question is implemention defined the same as implemention > defined in this case? No, it's undefined. Anything might happen. >> ISO/IEC 9899:1999 (E) >> >> 6.5 Expressions >> >> 5 If an exceptional condition occurs during the evaluation of an >> expression (that is, if the result is not mathematically defined or >> not in the range of representable values for its type), the behavior >> is undefined. >> > >>> I have verified the same behavior with 32-bit compilers and expected (val2=0) >>> with 16-bit compiler. I can correct this by shifting 18 in place of 2 as a >>> workaround. I want some verify my understanding for this point and another >>> way to get expected result (if any). >> >> Use an unsigned type. > >> 6.2.5 Types >> >> 9 ... A computation involving unsigned operands can never overflow, because a >> result that cannot be represented by the resulting unsigned integer >> type is reduced modulo the number that is one greater than the largest >> value that can be represented by the resulting type. >> > The result is still 0x8000 and not 0 as the original author expects. It could be 666. Demons may fly out of your nose. http://catb.org/jargon/html/N/nasal-demons.html Andrew.
