The bitfields are designed in assumption that fields contain unsigned integer values, thus extracting the values from the field implies zero-extending. Some drivers need to sign-extend their fields, and currently do it like: dc_re += sign_extend32(FIELD_GET(0xfff000, tmp), 11); dc_im += sign_extend32(FIELD_GET(0xfff, tmp), 11); It's error-prone because it relies on user to provide the correct index of the most significant bit and proper 32 vs 64 function flavor. Thus, introduce a FIELD_GET_SIGNED() macro, which is the more convenient and compiles (on x86_64) to just a couple instructions: shl and sar. Signed-off-by: Yury Norov --- include/linux/bitfield.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index 54aeeef1f0ec..35ef63972810 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -178,6 +178,22 @@ __FIELD_GET(_mask, _reg, "FIELD_GET: "); \ }) +/** + * FIELD_GET_SIGNED() - extract a signed bitfield element + * @mask: shifted mask defining the field's length and position + * @reg: value of entire bitfield + * + * Returns the sign-extended field specified by @_mask from the + * bitfield passed in as @_reg by masking and shifting it down. + */ +#define FIELD_GET_SIGNED(mask, reg) \ + ({ \ + __BF_FIELD_CHECK(mask, reg, 0U, "FIELD_GET_SIGNED: "); \ + ((__signed_scalar_typeof(mask))((long long)(reg) << \ + __builtin_clzll(mask) >> (__builtin_clzll(mask) + \ + __builtin_ctzll(mask))));\ + }) + /** * FIELD_MODIFY() - modify a bitfield element * @_mask: shifted mask defining the field's length and position -- 2.51.0