diff options
Diffstat (limited to 'include/linux/bitfield.h')
| -rw-r--r-- | include/linux/bitfield.h | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index c9be1657f03d..ebfa12f69501 100644 --- 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 |