Add generic C implementations of __paritysi2(), __paritydi2(), and __parityti2() as fallback functions in lib/parity.c. These functions compute the parity of a given integer using a bitwise approach and are marked with __weak, allowing architecture-specific implementations to override them. This patch serves as preparation for using __builtin_parity() by ensuring a fallback mechanism is available when the compiler does not inline the __builtin_parity(). Co-developed-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx> Signed-off-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx> Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx> --- lib/Makefile | 2 +- lib/parity.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 49 insertions(+), 1 deletion(-) create mode 100644 lib/parity.c diff --git a/lib/Makefile b/lib/Makefile index 7bab71e59019..45affad85ee4 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -51,7 +51,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \ bsearch.o find_bit.o llist.o lwq.o memweight.o kfifo.o \ percpu-refcount.o rhashtable.o base64.o \ once.o refcount.o rcuref.o usercopy.o errseq.o bucket_locks.o \ - generic-radix-tree.o bitmap-str.o + generic-radix-tree.o bitmap-str.o parity.o obj-y += string_helpers.o obj-y += hexdump.o obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o diff --git a/lib/parity.c b/lib/parity.c new file mode 100644 index 000000000000..a83ff8d96778 --- /dev/null +++ b/lib/parity.c @@ -0,0 +1,48 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * lib/parity.c + * + * Copyright (C) 2025 Kuan-Wei Chiu <visitorckw@xxxxxxxxx> + * Copyright (C) 2025 Yu-Chun Lin <eleanor15x@xxxxxxxxx> + * + * __parity[sdt]i2 can be overridden by linking arch-specific versions. + */ + +#include <linux/export.h> +#include <linux/kernel.h> + +/* + * One explanation of this algorithm: + * https://funloop.org/codex/problem/parity/README.html + */ +int __weak __paritysi2(u32 val); +int __weak __paritysi2(u32 val) +{ + val ^= val >> 16; + val ^= val >> 8; + val ^= val >> 4; + return (0x6996 >> (val & 0xf)) & 1; +} +EXPORT_SYMBOL(__paritysi2); + +int __weak __paritydi2(u64 val); +int __weak __paritydi2(u64 val) +{ + val ^= val >> 32; + val ^= val >> 16; + val ^= val >> 8; + val ^= val >> 4; + return (0x6996 >> (val & 0xf)) & 1; +} +EXPORT_SYMBOL(__paritydi2); + +int __weak __parityti2(u64 val); +int __weak __parityti2(u64 val) +{ + val ^= val >> 32; + val ^= val >> 16; + val ^= val >> 8; + val ^= val >> 4; + return (0x6996 >> (val & 0xf)) & 1; +} +EXPORT_SYMBOL(__parityti2); -- 2.34.1
