On Fri, 20 Apr 2007 16:20:59 -0400 James Bottomley <James.Bottomley@xxxxxxxxxxxx> wrote: > 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? bummer. > > + > > + > > #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. That works if we know the caller is treating the return value as 32 bits, but we don't know that. If we have #define upper_32_bits(x) ((x >> 16) >> 16) then upper_32_bits(0x8888777766665555) will return 0x88887777 if it's treated as 32-bits, but it'll return 0xffffffff88887777 if the caller is using 64-bits. I spose #define upper_32_bits(x) ((u32)((x >> 16) >> 16)) will do the trick. - 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
