On Fri, 2007-04-20 at 12:30 -0700, Andrew Morton wrote: > On Fri, 20 Apr 2007 14:50:06 -0400 > James Bottomley <James.Bottomley@xxxxxxxxxxxx> wrote: > > > > CONFIG_LBD=y gives us an additional 3kb of instructions on i386 > > > allnoconfig. Other architectures might do less well. It's not a huge > > > difference, but that's the way in which creeping bloatiness happens. > > > > OK, sure, but if we really care about this saving, then unconditionally > > casting to u64 is therefore wrong as well ... this is starting to open > > quite a large can of worms ... > > > > For the record, if we have to do this, I fancy sector_upper_32() ... we > > should already have some similar accessor for dma_addr_t as well. > > hm. How about this? > > --- a/include/linux/kernel.h~upper-32-bits > +++ a/include/linux/kernel.h > @@ -40,6 +40,17 @@ extern const char linux_proc_banner[]; > #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) > #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y)) > > +/** > + * upper_32_bits - return bits 32-63 of a number > + * @n: the number we're accessing > + * > + * A basic shift-right of a 64- or 32-bit quantity. Use this to suppress > + * the "right shift count >= width of type" warning when that quantity is > + * 32-bits. > + */ > +#define upper_32_bits(n) (((u64)(n)) >> 32) Won't this have the unwanted side effect of promoting everything in a calculation to long long on 32 bit platforms, even if n was only 32 bits? > + > + > #define KERN_EMERG "<0>" /* system is unusable */ > #define KERN_ALERT "<1>" /* action must be taken immediately */ > #define KERN_CRIT "<2>" /* critical conditions */ > _ > > It seems to generate the desired code. I avoided Alan's ((n >> 31) >> 1) > trick because it'll generate peculiar results with signed 64-bit > quantities. I've seen the trick done similarly with ((n >> 16) >> 16) which shouldn't have the issue. James - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
