clang - odd macro / conditional expansion behaviour?
Adrian Chadd
adrian at freebsd.org
Tue Mar 12 03:17:10 UTC 2013
I've hit this rather amusing clang behaviour:
In file included from
/usr/home/adrian/work/freebsd/ath/head/src/sys/modules/ath/../../contrib/sys/dev/ath/ath_hal/ar9300/ar9300_eeprom.c:21:
/usr/home/adrian/work/freebsd/ath/head/src/sys/modules/ath/../../contrib/sys/dev/ath/ath_hal/ar9300/ar9300template_generic.h:107:3:
error: implicit conversion from 'int' to
'u_int8_t' (aka 'unsigned char') changes value from -477 to 35
[-Werror,-Wconstant-conversion]
FREQ2FBIN(2412, 1),
^~~~~~~~~~~~~~~~~~
/usr/home/adrian/work/freebsd/ath/head/src/sys/modules/ath/../../contrib/sys/dev/ath/ath_hal/ar9300/ar9300eep.h:136:65:
note: expanded from macro 'FREQ2FBIN'
(((y) == HAL_FREQ_BAND_2GHZ) ? ((x) - 2300) : (((x) - 4800) / 5))
~~~~~~~~~~~~~^~~
.. now, HAL_FREQ_BAND_2GHZ is defined here as:
typedef enum {
HAL_FREQ_BAND_5GHZ = 0,
HAL_FREQ_BAND_2GHZ = 1,
} HAL_FREQ_BAND;
And:
#define FREQ2FBIN(x,y) \
(((y) == HAL_FREQ_BAND_2GHZ) ? ((x) - 2300) : (((x) - 4800) / 5))
And all of those macros here have '1' in the second field, yet when
they're expanded they evaluate as if it were false.
So, what's going on? :-) gcc is fine with this. :)
Thanks!
Adrian
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