On Fri, 20 Apr 2007 14:50:06 -0400
James Bottomley <[email protected]> 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)
+
+
#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.
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