Author: Robert Hyatt
Date: 07:25:29 03/29/04
Go up one level in this thread
On March 28, 2004 at 23:35:08, Russell Reagan wrote: >On March 28, 2004 at 12:29:42, Eugene Nalimov wrote: > >>There are situations when VC can hoist signed lengthening convert out of the >>loop, but cannot hoist unsigned convert. Reason is C/C++ semantics -- according >>to the Standard signed overflow results in undefined behavior, so compiler can >>assume that there would be no overflow. > >Is there any penalty for copying different data sizes? Example: > >unsigned char one_byte; // sizeof(unsigned char) == 1 >unsigned short two_bytes; // sizeof(unsigned short) == 2 >unsigned long four_bytes; // sizeof(unsigned long) == 4 > >one_byte = four_bytes; >one_byte = two_bytes; >two_bytes = one_byte; >two_bytes = four_bytes; >four_bytes = one_byte; >four_bytes = two_bytes; > >Are there any penalties for any of the above copies? signed-shorter copied to signed-longer requires a sign extension... Others are ok and unsigned doesn't have that problem at all...
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