On Sun, Dec 06, 2020 at 06:24:05PM +0700, Bui Quang Minh wrote: > On Sat, Dec 05, 2020 at 10:15:11AM -0500, Alan Stern wrote: > > On Sat, Dec 05, 2020 at 07:47:01PM +0700, Minh Bùi Quang wrote: > > > Vào Th 6, 4 thg 12, 2020 vào lúc 23:12 Alan Stern > > > <stern@xxxxxxxxxxxxxxxxxxx> đã viết: > > > > Does this initialization end up using less memory than an explicit > > > > memset() call? > > > > > > You mean speed? > > > > No, I mean memory space. > > > > A memset call requires a certain amount of instruction space (to push > > the arguments and make the call) but no static data space. > > Initialization requires some instruction space (to copy the data) and > > static data space as well (to hold the data that is to be copied). > > > > Alan Stern > > > > Thank you for your clarification, I didn't think about it before. > > As I check when compiling the code, with MAX_NUM_UDC=32 the initialization > becomes > > xor eax,eax > mov ecx,0x40 > rep stos DWORD PTR es:[rdi],eax > > With MAX_NUM_UDC=2, the initialization becomes > > mov QWORD PTR [rbp-0x30],0x0 > mov QWORD PTR [rbp-0x28],0x0 > > As I see, initialization does not require additional static data space. > Am I right? Ah, okay, good. I didn't realize the compiler was smart enough to do this. Thanks for checking. Alan Stern
