[PATCH v3 00/16] Introduce and use generic parity16/32/64 helper

[H. Peter Anvin]

On March 6, 2025 8:25:25 AM PST, Kuan-Wei Chiu <visitorckw at gmail.com> 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 at gmail.com>
>Signed-off-by: Yu-Chun Lin <eleanor15x at gmail.com>
>Signed-off-by: Kuan-Wei Chiu <visitorckw at gmail.com>
>---
>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@gmail.com/
>v2: https://lore.kernel.org/lkml/20250301142409.2513835-1-visitorckw@gmail.com/
>
>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(-)
>

(int)true most definitely is guaranteed to be 1.