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Subject[PATCH v2] bitfield.h: add FIELD_MAX() and field_max()
Date
Define FIELD_MAX(), which supplies the maximum value that can be
represented by a bitfield. Define field_max() as well, to go
along with the lower-case forms of the field mask functions.

Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
---
v2: Added Acked-by from Jakub.

David, I added you to this because it's probably easiest to take
this change in through your tree with the rest of the IPA code
(which uses field_max(), defined here).

-Alex

include/linux/bitfield.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 4bbb5f1c8b5b..48ea093ff04c 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -55,6 +55,19 @@
(1ULL << __bf_shf(_mask))); \
})

+/**
+ * FIELD_MAX() - produce the maximum value representable by a field
+ * @_mask: shifted mask defining the field's length and position
+ *
+ * FIELD_MAX() returns the maximum value that can be held in the field
+ * specified by @_mask.
+ */
+#define FIELD_MAX(_mask) \
+ ({ \
+ __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: "); \
+ (typeof(_mask))((_mask) >> __bf_shf(_mask)); \
+ })
+
/**
* FIELD_FIT() - check if value fits in the field
* @_mask: shifted mask defining the field's length and position
@@ -110,6 +123,7 @@ static __always_inline u64 field_mask(u64 field)
{
return field / field_multiplier(field);
}
+#define field_max(field) ((typeof(field))field_mask(field))
#define ____MAKE_OP(type,base,to,from) \
static __always_inline __##type type##_encode_bits(base v, base field) \
{ \
--
2.20.1
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