user/sven/linux.git/include/linux/bitrev.h, branch v4.9.309

include/linux/bitrev.h: fix constant bitrev

2019-04-17T06:36:46Z

commit 6147e136ff5071609b54f18982dea87706288e21 upstream. clang points out with hundreds of warnings that the bitrev macros have a problem with constant input: drivers/hwmon/sht15.c:187:11: error: variable '__x' is uninitialized when used within its own initialization [-Werror,-Wuninitialized] u8 crc = bitrev8(data->val_status & 0x0F); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/bitrev.h:102:21: note: expanded from macro 'bitrev8' __constant_bitrev8(__x) : \ ~~~~~~~~~~~~~~~~~~~^~~~ include/linux/bitrev.h:67:11: note: expanded from macro '__constant_bitrev8' u8 __x = x; \ ~~~ ^ Both the bitrev and the __constant_bitrev macros use an internal variable named __x, which goes horribly wrong when passing one to the other. The obvious fix is to rename one of the variables, so this adds an extra '_'. It seems we got away with this because - there are only a few drivers using bitrev macros - usually there are no constant arguments to those - when they are constant, they tend to be either 0 or (unsigned)-1 (drivers/isdn/i4l/isdnhdlc.o, drivers/iio/amplifiers/ad8366.c) and give the correct result by pure chance. In fact, the only driver that I could find that gets different results with this is drivers/net/wan/slic_ds26522.c, which in turn is a driver for fairly rare hardware (adding the maintainer to Cc for testing). Link: http://lkml.kernel.org/r/20190322140503.123580-1-arnd@arndb.de Fixes: 556d2f055bf6 ("ARM: 8187/1: add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction") Signed-off-by: Arnd Bergmann Reviewed-by: Nick Desaulniers Cc: Zhao Qiang Cc: Yalin Wang Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

ARM: 8187/1: add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction

2014-12-22T16:43:06Z

this change add CONFIG_HAVE_ARCH_BITREVERSE config option, so that we can use some architecture's bitrev hardware instruction to do bitrev operation. Introduce __constant_bitrev* macro for constant bitrev operation. Change __bitrev16() __bitrev32() to be inline function, don't need export symbol for these tiny functions. Signed-off-by: Yalin Wang Acked-by: Will Deacon Signed-off-by: Russell King

lib: export bitrev16

2008-06-06T18:29:10Z

Bluetooth will be able to use this. Signed-off-by: Harvey Harrison Cc: Marcel Holtmann Cc: Dave Young Cc: Akinobu Mita Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] bit reverse library

2006-12-08T16:28:39Z

This patch provides two bit reverse functions and bit reverse table. - reverse the order of bits in a u32 value u8 bitrev8(u8 x); - reverse the order of bits in a u32 value u32 bitrev32(u32 x); - byte reverse table const u8 byte_rev_table[256]; Signed-off-by: Akinobu Mita Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds