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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>
16 lines
364 B
C
16 lines
364 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_GENERIC_BITOPS_BUILTIN_FFS_H_
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#define _ASM_GENERIC_BITOPS_BUILTIN_FFS_H_
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/**
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* ffs - find first bit set
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* @x: the word to search
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*
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* This is defined the same way as
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* the libc and compiler builtin ffs routines, therefore
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* differs in spirit from ffz (man ffs).
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*/
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#define ffs(x) __builtin_ffs(x)
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#endif
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