On 10/27/2011 11:29 AM, David Brown wrote: > > Q_new can be simplified to: > > Q_new = Q_old + 2^(i-1) . (Di_old + Di_new) > > "Multiplying" by 2 is relatively speaking quite time-consuming in > GF(2^8). "Multiplying" by 2^(i-1) can be done by either pre-calculating > a multiply table, or using a loop to repeatedly multiply by 2. > Multiplying by 2 is cheap. Multiplying by an arbitrary number is more expensive, in the absence of tricks that can be played on specific hardware implementations (e.g. SSSE3) as mentioned in my paper. > > I don't know what compiler versions are typically used to compile the > kernel, but from gcc 4.4 onwards there is a "target" function attribute > that can be used to change the target cpu for a function. What this > means is that the C code can be written once, and multiple versions of > it can be compiled with features such as "sse", "see4", "altivec", > "neon", etc. And newer versions of the compiler are getting better at > using these cpu features automatically. It should therefore be > practical to get high-speed code suited to the particular cpu you are > running on, without needing hand-written SSE/Altivec assembly code. That > would save a lot of time and effort on writing, testing and maintenance. > Nice in theory; doesn't work in practice in my experience. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
