[U-Boot] [PATCH] fix print_size printing fractional gigabyte numbers on 32-bit platforms
Timur Tabi
timur at freescale.com
Wed Mar 31 00:32:59 CEST 2010
Scott Wood wrote:
> It would make the 10 * (...) product 64-bit regardless of phys_size_t,
> without changing the function signature (overflow is an internal
> implementation detail).
You are right that (n * d) is evaluated as a 32-bit integer:
print_size(5905580032)= 6.35 GB
However, changing "10" to "10ULL" does not fix this. I think this is because we are both expecting integer sizes to commute across arithmetic operations. That is, I assumed that:
u64 - (u32 * u32)
would be treated as
u64 - ((u64)u32 * u32)
And you assumed that
u64 * (u32 - u32)
would be treated as
u64 * (u32 - (u64) u32)
Both appear to be wrong. If we want to treat (n * d) as a u64, we need to be explicit. Casting "(n * d)" to a u64 just doesn't work. We have to cast (or make) either 'n' or 'd' to a u64.
I think the simplest approach is make 'd' into a u64.
--
Timur Tabi
Linux kernel developer at Freescale
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