On Mon, Nov 26, 2012 at 03:17:45PM -0800, Zach Brown wrote: > > This function efficiently counts the number of bits in a block of > > memory. > > Would it be worth the annoying build- and run-time machinery to detect > and use the -msse4.2 __builtin_popcount() gcc intrinsic? I thought about doing it, but I was in a bit of a hurry implementing this patch set, and I wasn't even sure how to correctly implement the build- and run-time machinery (i.e., detecting whether the gcc you're compiling with supports __builtin_popcount, and implementing a run-time fallback is the CPU doesn't support popcount instruction --- which by the way isn't properly part of SSE 4.2; it has its own separate CPUID bit, IIRC). Is there some userspace application licensed under LGPLv2 which does this cleanly from which I could borrow code? I suppose I should first check and see how much difference it makes to with a hard-coded use __builtin_popcnt(). If it makes a sufficiently large improvement, it's probably worth the hair of implementing the fallback machinery. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
