On 05/23/2012 09:47 AM, H. Peter Anvin wrote: > > BIT(0), okay. I thought we were talking about BIT_64() here... > > Any reason we can't just tell people to use BIT() for a native "unsigned > long" type (32/64 bits) and BIT_64() if they really want a 64-bit result? > > There are good reasons for the latter. Consider, for example: > > u64 msr; > ... > msr &= ~BIT_64(1); > > This *better* not be an unsigned 32 bit value, or we just chopped off > the upper half. In this case and similar ones the 64-bitness of the > result really matters. > To better clarify my concern: my concern is that if we make BIT() be a DWIM type, it will appear to work in most situations. As such, we'll see things in headers like: #define MSR_BLAH_FOO BIT(31) #define MSR_BLAH_BAR BIT(32) ... and *almost all the time* the above will work. But if you use MSR_BLAH_FOO inverted, then you get truncation. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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