On Thursday, 18 October 2012 at 02:36:59 UTC, bearophile wrote:
uint foo(in uint x) pure nothrow {
return (x << 11) | (x >> (32 - 11));
}
Why would you write that instead of using rol(x, 11) today?
uint rol(in uint x, in uint y) pure nothrow {
return (x << y) | (x >> (32 - y));
}
uint foo(in uint x) pure nothrow {
return rol(x, 11);
}
the rest is the same. Compile it and see a rol instruction,
inlined, in the main function.
Though there is a bit of extra spam around it, some movs that
don't seem necessary to me.
Here's the top function so you can see the movs:
00000000 <_D5test43rolFNaNbxkxkZk>:
0: 55 push ebp
1: 8b ec mov ebp,esp
3: 50 push eax
4: 8b 45 08 mov eax,DWORD PTR [ebp+0x8]
7: 8b 4d fc mov ecx,DWORD PTR [ebp-0x4]
a: 8b e5 mov esp,ebp
c: d3 c0 rol eax,cl
e: 5d pop ebp
f: c2 04 00 ret 0x4
12: 90 nop
13: 90 nop
Perhaps we should add that rol function to the stdlib to save
people from quickly doing it themselves, but there's no need to
do anything beyond this simple function.
