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    SubjectRe: [PATCH 10/36] tty/vt: consolemap: introduce UNI_*() macros
    On Wed, 8 Jun 2022, Jiri Slaby wrote:

    > On 08. 06. 22, 8:59, Jiri Slaby wrote:
    > > On 07. 06. 22, 15:47, Ilpo Järvinen wrote:
    > > > On Tue, 7 Jun 2022, Jiri Slaby wrote:
    > > >
    > > > > The code currently does shift, OR, and AND logic directly in the code.
    > > > > It is not much obvious what happens there. Therefore define four macros
    > > > > for that purpose and use them in the code. We use GENMASK() so that it
    > > > > is clear which bits serve what purpose:
    > > > > - UNI_GLYPH: bits  0.. 5
    > > > > - UNI_ROW:   bits  6..10
    > > > > - UNI_DIR:   bits 11..31
    > > > >
    > > > > Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    > > > > ---
    > > > >   drivers/tty/vt/consolemap.c | 21 +++++++++++++--------
    > > > >   1 file changed, 13 insertions(+), 8 deletions(-)
    > > > >
    > > > > diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
    > > > > index 016c1a0b4290..e5fd225e87bd 100644
    > > > > --- a/drivers/tty/vt/consolemap.c
    > > > > +++ b/drivers/tty/vt/consolemap.c
    > > > > @@ -190,6 +190,11 @@ static int inv_translate[MAX_NR_CONSOLES];
    > > > >   #define UNI_DIR_ROWS    32U
    > > > >   #define UNI_ROW_GLYPHS    64U
    > > > > +#define UNI_DIR(uni)        ( (uni)                   >> 11)
    > > > > +#define UNI_ROW(uni)        (((uni) & GENMASK(10, 6)) >>  6)
    > > >
    > > > This is opencoding what FIELD_GET() does. Maybe just define these as
    > > > masks and use FIELD_GET in the code below.
    > >
    > > Ah, great -- I was thinking there should be something for that purpose
    > > already, but didn't find this. But let's define these UNI_* macros using
    > > appropriate FIELD_GET(). (And not using FIELD_GET() in the code.)
    > >
    > > > > +#define UNI_GLYPH(uni)        ( (uni) & GENMASK( 5, 0))
    > > thanks,
    >
    > JFYI, I ended up with this diff to the original approach:
    > --- a/drivers/tty/vt/consolemap.c
    > +++ b/drivers/tty/vt/consolemap.c
    > @@ -23,6 +23,8 @@
    > * stack overflow.
    > */
    >
    > +#include <linux/bitfield.h>
    > +#include <linux/bits.h>
    > #include <linux/module.h>
    > #include <linux/kd.h>
    > #include <linux/errno.h>
    > @@ -190,10 +192,17 @@ static int inv_translate[MAX_NR_CONSOLES];
    > #define UNI_DIR_ROWS 32U
    > #define UNI_ROW_GLYPHS 64U
    >
    > -#define UNI_DIR(uni) ( (uni) >> 11)
    > -#define UNI_ROW(uni) (((uni) & GENMASK(10, 6)) >> 6)
    > -#define UNI_GLYPH(uni) ( (uni) & GENMASK( 5, 0))
    > -#define UNI(dir, row, glyph) (((dir) << 11) | ((row) << 6) | (glyph))
    > +#define UNI_DIR_BITS(max) GENMASK((max), 11)
    > +#define UNI_ROW_BITS GENMASK(10, 6)
    > +#define UNI_GLYPH_BITS GENMASK( 5, 0)
    > +
    > +#define UNI_DIR(uni) FIELD_GET(UNI_DIR_BITS(sizeof(uni) * 8 - 1), (uni))

    That would be * BITS_PER_BYTE. But see below.

    > +#define UNI_ROW(uni) FIELD_GET(UNI_ROW_BITS, (uni))
    > +#define UNI_GLYPH(uni) FIELD_GET(UNI_GLYPH_BITS, (uni))
    > +
    > +#define UNI(dir, row, glyph) (FIELD_PREP(UNI_DIR_BITS(31), (dir)) | \
    > + FIELD_PREP(UNI_ROW_BITS, (row)) | \
    > + FIELD_PREP(UNI_GLYPH_BITS, (glyph)))
    >
    > /**
    > * struct uni_pagedict -- unicode directory
    >
    > =======================================================
    >
    > More text, but easier to follow, I think. except the UNI_DIR_BITS() has to
    > have a parameter, otherwise compilation raises a too-big value warning with
    > use of UNI_DIR() in con_insert_unipair() where uni is only of ushort type.

    It doesn't raise any warnings if I do:

    #define UNI_DIR_BITS GENMASK(15, 11)

    As UNI_DIRS is 32 it cannot ever be larger than that?

    > Alternatively, we can cast uni to u32, but that produces worse assembly
    > (extensions to u32 here and there).

    --
    i.
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