https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63420
Bug ID: 63420
Summary: GCC 4.8.2: Bitshift second operand range not as per
manual.
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: aainscow at uk dot ibm.com
Created attachment 33625
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33625&action=edit
Demo code
Most likely this is simply a problem with the GCC manual.
The GCC documentation states (30th Sept 2014):
--
You use the left-shift operator << to shift its first operand's bits to the
left. The second operand denotes the number of bit places to shift. Bits
shifted off the left side of the value are discarded; new bits added on the
right side will all be 0.
...
For both << and >>, if the second operand is greater than the bit-width of the
first operand, or the second operand is negative, the behavior is undefined.
--
NOTE: "greater than" not "greater than or equal to".
The following code should therefore not be undefined and return 0.
int main() {
int a = sizeof(int)*8;
return ((int)1) << a;
}
However:
aainscow@morwenna:~/cake$ gcc bitshift_bug.c
aainscow@morwenna:~/cake$ ./a.out ; echo $?
1
Most likely this is a problem with documentation.
