[PATCH v4 6/9] linux/bitfield.h: Add primitives for manipulating bitfields both in host- and fixed-endian

[Sylwester Nawrocki]

From: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>

Imports Al Viro's original Linux commit 00b0c9b82663a, which contains
an in depth explanation and two fixes from Johannes Berg:
 e7d4a95da86e0 "bitfield: fix *_encode_bits()",
 37a3862e12382 "bitfield: add u8 helpers".

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>
[s.nawrocki: added empty lines between functions and macros]
Signed-off-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
---
Changes since v3:
 - none.
Changes since v2:
 - added some more missing whitespaces as pointed out by checkpatch.pl.
Changes since v1:
 - added empty lines between functions and macros.
Changes since RFC:
 - new patch.
---
 include/linux/bitfield.h | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 8b9d6ff..7ad8b08 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -103,4 +103,56 @@
 		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
 	})
 
+extern void __compiletime_error("value doesn't fit into mask")
+__field_overflow(void);
+extern void __compiletime_error("bad bitfield mask")
+__bad_mask(void);
+
+static __always_inline u64 field_multiplier(u64 field)
+{
+	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
+		__bad_mask();
+	return field & -field;
+}
+
+static __always_inline u64 field_mask(u64 field)
+{
+	return field / field_multiplier(field);
+}
+
+#define ____MAKE_OP(type, base, to, from)				\
+static __always_inline __##type type##_encode_bits(base v, base field)	\
+{									\
+	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
+		__field_overflow();					\
+	return to((v & field_mask(field)) * field_multiplier(field));	\
+}									\
+static __always_inline __##type type##_replace_bits(__##type old,	\
+					base val, base field)		\
+{									\
+	return (old & ~to(field)) | type##_encode_bits(val, field);	\
+}									\
+static __always_inline void type##p_replace_bits(__##type * p,		\
+					base val, base field)		\
+{									\
+	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
+}									\
+static __always_inline base type##_get_bits(__##type v, base field)	\
+{									\
+	return (from(v) & field) / field_multiplier(field);		\
+}
+
+#define __MAKE_OP(size)							\
+	____MAKE_OP(le##size, u##size, cpu_to_le##size, le##size##_to_cpu) \
+	____MAKE_OP(be##size, u##size, cpu_to_be##size, be##size##_to_cpu) \
+	____MAKE_OP(u##size, u##size, ,)
+
+____MAKE_OP(u8, u8, ,)
+__MAKE_OP(16)
+__MAKE_OP(32)
+__MAKE_OP(64)
+
+#undef __MAKE_OP
+#undef ____MAKE_OP
+
 #endif
-- 
2.7.4