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- From e2192de59e457aef8d1f055a452131f0b3e5d097 Mon Sep 17 00:00:00 2001
- From: Johannes Berg <[email protected]>
- Date: Wed, 18 Jan 2023 14:26:53 +0100
- Subject: [PATCH] bitfield: add FIELD_PREP_CONST()
- Neither FIELD_PREP() nor *_encode_bits() can be used
- in constant contexts (such as initializers), but we
- don't want to define shift constants for all masks
- just for use in initializers, and having checks that
- the values fit is also useful.
- Therefore, add FIELD_PREP_CONST() which is a smaller
- version of FIELD_PREP() that can only take constant
- arguments and has less friendly (but not less strict)
- error checks, and expands to a constant value.
- Signed-off-by: Johannes Berg <[email protected]>
- Link: https://lore.kernel.org/r/20230118142652.53f20593504b.Iaeea0aee77a6493d70e573b4aa55c91c00e01e4b@changeid
- Signed-off-by: Johannes Berg <[email protected]>
- ---
- include/linux/bitfield.h | 26 ++++++++++++++++++++++++++
- 1 file changed, 26 insertions(+)
- --- a/include/linux/bitfield.h
- +++ b/include/linux/bitfield.h
- @@ -115,6 +115,32 @@
- ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
- })
-
- +#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
- +
- +/**
- + * FIELD_PREP_CONST() - prepare a constant bitfield element
- + * @_mask: shifted mask defining the field's length and position
- + * @_val: value to put in the field
- + *
- + * FIELD_PREP_CONST() masks and shifts up the value. The result should
- + * be combined with other fields of the bitfield using logical OR.
- + *
- + * Unlike FIELD_PREP() this is a constant expression and can therefore
- + * be used in initializers. Error checking is less comfortable for this
- + * version, and non-constant masks cannot be used.
- + */
- +#define FIELD_PREP_CONST(_mask, _val) \
- + ( \
- + /* mask must be non-zero */ \
- + BUILD_BUG_ON_ZERO((_mask) == 0) + \
- + /* check if value fits */ \
- + BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
- + /* check if mask is contiguous */ \
- + __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))) + \
- + /* and create the value */ \
- + (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)) \
- + )
- +
- /**
- * FIELD_GET() - extract a bitfield element
- * @_mask: shifted mask defining the field's length and position
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