On March 6, 2025 8:25:25 AM PST, Kuan-Wei Chiu <visitorckw@xxxxxxxxx> wrote: >Several parts of the kernel contain redundant implementations of parity >calculations for 16/32/64-bit values. Introduces generic >parity16/32/64() helpers in bitops.h, providing a standardized >and optimized implementation. > >Subsequent patches refactor various kernel components to replace >open-coded parity calculations with the new helpers, reducing code >duplication and improving maintainability. > >Co-developed-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx> >Signed-off-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx> >Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx> >--- >In v3, I use parityXX() instead of the parity() macro since the >parity() macro may generate suboptimal code and requires special hacks >to make GCC happy. If anyone still prefers a single parity() macro, >please let me know. > >Additionally, I changed parityXX() << y users to !!parityXX() << y >because, unlike C++, C does not guarantee that true casts to int as 1. > >Changes in v3: >- Avoid using __builtin_parity. >- Change return type to bool. >- Drop parity() macro. >- Change parityXX() << y to !!parityXX() << y. > > >Changes in v2: >- Provide fallback functions for __builtin_parity() when the compiler > decides not to inline it >- Use __builtin_parity() when no architecture-specific implementation > is available >- Optimize for constant folding when val is a compile-time constant >- Add a generic parity() macro >- Drop the x86 bootflag conversion patch since it has been merged into > the tip tree > >v1: https://lore.kernel.org/lkml/20250223164217.2139331-1-visitorckw@xxxxxxxxx/ >v2: https://lore.kernel.org/lkml/20250301142409.2513835-1-visitorckw@xxxxxxxxx/ > >Kuan-Wei Chiu (16): > bitops: Change parity8() return type to bool > bitops: Add parity16(), parity32(), and parity64() helpers > media: media/test_drivers: Replace open-coded parity calculation with > parity8() > media: pci: cx18-av-vbi: Replace open-coded parity calculation with > parity8() > media: saa7115: Replace open-coded parity calculation with parity8() > serial: max3100: Replace open-coded parity calculation with parity8() > lib/bch: Replace open-coded parity calculation with parity32() > Input: joystick - Replace open-coded parity calculation with > parity32() > net: ethernet: oa_tc6: Replace open-coded parity calculation with > parity32() > wifi: brcm80211: Replace open-coded parity calculation with parity32() > drm/bridge: dw-hdmi: Replace open-coded parity calculation with > parity32() > mtd: ssfdc: Replace open-coded parity calculation with parity32() > fsi: i2cr: Replace open-coded parity calculation with parity32() > fsi: i2cr: Replace open-coded parity calculation with parity64() > Input: joystick - Replace open-coded parity calculation with > parity64() > nfp: bpf: Replace open-coded parity calculation with parity64() > > drivers/fsi/fsi-master-i2cr.c | 18 ++----- > .../drm/bridge/synopsys/dw-hdmi-ahb-audio.c | 8 +-- > drivers/input/joystick/grip_mp.c | 17 +----- > drivers/input/joystick/sidewinder.c | 24 ++------- > drivers/media/i2c/saa7115.c | 12 +---- > drivers/media/pci/cx18/cx18-av-vbi.c | 12 +---- > .../media/test-drivers/vivid/vivid-vbi-gen.c | 8 +-- > drivers/mtd/ssfdc.c | 20 ++----- > drivers/net/ethernet/netronome/nfp/nfp_asm.c | 7 +-- > drivers/net/ethernet/oa_tc6.c | 19 ++----- > .../broadcom/brcm80211/brcmsmac/dma.c | 16 +----- > drivers/tty/serial/max3100.c | 3 +- > include/linux/bitops.h | 52 +++++++++++++++++-- > lib/bch.c | 14 +---- > 14 files changed, 77 insertions(+), 153 deletions(-) > !!x is used with a value that is not necessary booleanized already, and is exactly equivalent to (x ? true : false). It is totally redundant on a value known to be bool. If (int)true wasn't inherently 1, then !! wouldn't work either. There was a time when some code would use as a temporary hack: typedef enum { false, true } bool; ... when compiling on pre-C99 compilers; in that case a (bool) case wouldn't necessarily work as expected, whereas !! would. Furthermore, unlike (bool), !! works in the preprocessor.
