Messages in this thread | | | Date | Fri, 30 Nov 2007 14:36:54 +0100 | From | Jean Delvare <> | Subject | Re: [patch/rfc 2/4] pcf875x I2C GPIO expander driver |
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Hi Bill,
On Fri, 30 Nov 2007 07:04:10 -0600, Bill Gatliff wrote: > Jean Delvare wrote: > > !!(value & (1 << offset)) > > is more efficiently written > > (value >> offset) & 1 > > ... but not more efficiently implemented. > > Your version requires code to do the shift on live data at runtime. > David's version lets the compiler create the mask once, at compile-time.
I don't understand. How could the compiler create the mask at compile-time when "offset" is only known at runtime?
Anyway, I just checked and gcc (4.1.2 on x86_86) generates the same code for both expressions, so there's not much to argue about. David, feel free to ignore my comment if you prefer your implementation :)
-- Jean Delvare - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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