diff options
| author | Sean Anderson <sean.anderson@seco.com> | 2023-07-31 17:27:33 -0400 |
|---|---|---|
| committer | Tom Rini <trini@konsulko.com> | 2023-08-17 16:39:20 -0400 |
| commit | 726a802fdaf1ffb4ca95ebf6910a738781137ef5 (patch) | |
| tree | 7d2df62ee83092d7b8b6032f48a980b2a212df8c /include/asm-generic/bitops/builtin-__ffs.h | |
| parent | 14ba0a8bbc342a677982acc787ae542b84ed7993 (diff) | |
arm: Use builtins for ffs/fls
Since ARMv5, the clz instruction allows for efficient implementation of
ffs/fls with builtins. Until ARMv7 (with Thumb-2), this instruction is
only available in ARM mode. LTO makes it difficult to force specific
functions to be in ARM mode, as it is effectively a form of very
aggressive inlining. To work around this, fls/ffs are implemented in
assembly for ARMv5 and ARMv6 when compiling U-Boot in Thumb mode.
Overall, this saves around 75 bytes per call.
This code is synced with v5.15 of the Linux kernel.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Diffstat (limited to 'include/asm-generic/bitops/builtin-__ffs.h')
| -rw-r--r-- | include/asm-generic/bitops/builtin-__ffs.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/include/asm-generic/bitops/builtin-__ffs.h b/include/asm-generic/bitops/builtin-__ffs.h new file mode 100644 index 00000000000..87024da44d1 --- /dev/null +++ b/include/asm-generic/bitops/builtin-__ffs.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_GENERIC_BITOPS_BUILTIN___FFS_H_ +#define _ASM_GENERIC_BITOPS_BUILTIN___FFS_H_ + +/** + * __ffs - find first bit in word. + * @word: The word to search + * + * Undefined if no bit exists, so code should check against 0 first. + */ +static __always_inline unsigned long __ffs(unsigned long word) +{ + return __builtin_ctzl(word); +} + +#endif |