http://d.puremagic.com/issues/show_bug.cgi?id=3738
Witold Baryluk <bary...@smp.if.uj.edu.pl> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |NEW
--- Comment #3 from Witold Baryluk <bary...@smp.if.uj.edu.pl> 2010-01-24
08:35:08 PST ---
One can observe that ?: line (branch2)
_x = (y < v || y >= 2147483647) ? ((y+1) & 0x7fff_ffffu) : y;
can be changed , first to not contain not needed y<v, to (branch1)
_x = (y >= 2147483647) ? ((y+1) & 0x7fff_ffffu) : y;
or even remove branch completly (branchlessA)
_x = (y & 0x7fff_ffff) + (y >> 31);
and possibly rearange terms (branchlessB)
_x = (y + (y >> 31)) & 0x7fff_ffff;
MinstdRnd0
standard: 44.65 s
inline: 41.11 s
standard with tricks (2 branches): 17.08 s
inline with tricks (2 branches): 17.04 s
standard with tricks (1 branch): 15.24 s
inline with tricks (1 branch): 13.59 s
standard with tricks (branchlesA): 16.50 s
inline with tricks (branchelesA): 15.82 s
standard with tricks (branchlesB): 17.74 s
inline with tricks (branchelesB): 15.30 s
MinstdRnd
standard: 44.95 s
inline: 41.17 s
standard with tricks (2 branch): 17.04 s
inline with tricks (2 branche): 17.03 s
standard with tricks (1 branch): 15.29 s
inline with tricks (1 branche): 13.54 s
standard with tricks (branchlesA): 16.46 s
inline with tricks (branchelessA): 15.88 s
standard with tricks (branchlesB): 18.10 s
inline with tricks (branchelessB): 15.31 s
So fastest is currently branch1 version.
Updated patch:
void popFront()
{
static if (m)
- _x = cast(UIntType) ((cast(ulong) a * _x + c) % m);
+ static if (is(UIntType == uint) && m == 4294967295uL) {
+ const ulong x = (cast(ulong) a * _x + c);
+ const ulong v = x >> 32;
+ const ulong w = (x & 0xffff_ffffuL);
+ const uint y = cast(uint)(v+w);
+ _x = (y < v || y >= 4294967295u) ? (y+1) : y;
+ } else static if (is(UIntType == uint) && m == 2147483647u) {
+ const ulong x = (cast(ulong) a * _x + c);
+ const ulong v = x >> 31;
+ const ulong w = (x & 0x7fff_ffffuL);
+ const uint y = cast(uint)(v+w);
+ _x = (y >= 2147483647u) ? ((y+1) & 0x7fff_ffffu) : y;
+ } else {
+ _x = cast(UIntType) ((cast(ulong) a * _x + c) % m);
+ }
else
_x = a * _x + c;
}
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