22 May
2009
22 May
'09
9:55 a.m.
dmitrey schrieb:
Hi all, I expected to have some speedup via using ldexp or multiplying an array by a power of 2 (doesn't it have to perform a simple shift of mantissa?), but I don't see the one.
# Let me also note - # 1) using b = 2 * ones(N) or b = zeros(N) doesn't yield any speedup vs b = rand() # 2) using A * 2.0 (or mere 2) instead of 2.1 doesn't yield any speedup, despite it is exact integer power of 2.
On recent processors multiplication is very fast and takes 1.5 clock cycles (float, double precision), independent of the values. There is very little gain by using bit shift operators. Gregor