Re: [Qemu-devel] [PATCH v5 13/20] hw/acpi/aml-build: Add ToUUID macro

[Shannon Zhao]

On 2015/4/28 17:48, Shannon Zhao wrote:
> On 2015/4/28 17:35, Igor Mammedov wrote:
> > On Tue, 28 Apr 2015 16:52:19 +0800
> > Shannon Zhao <address@hidden> wrote:
> >
> > > On 2015/4/28 16:15, Igor Mammedov wrote:
> > > > > > btw:
> > > > > > > > whole thing might be simpler if an intermediate conversion is avoided,
> > > > > > > > just pack buffer as in spec byte by byte:
> > > > > > > >
> > > > > > > > /* format: aabbccdd-eeff-gghh-iijj-kkllmmnnoopp */
> > > > > > > > assert(strlen(uuid) == ...);
> > > > > > > > build_append_byte(var->buf, HEX2BYTE(uuid[3]); /* dd */
> > > > > >
> > > > > > use build_append_byte(var->buf, HEX2BYTE(uuid + 7); ?
> > > > > >
> > > > > > > > build_append_byte(var->buf, HEX2BYTE(uuid[2]); /* cc */
> > > > > >
> > > > > > use build_append_byte(var->buf, HEX2BYTE(uuid + 5); ?
> > > > if you mean hyphens /-/ then they are not encoded,
> > > > but you surely can add checks for them to make sure that
> > > > UUID format is as expected.
> > >
> > > I mean uuid[3] points to b not dd. Maybe use following way:
> > >
> > > static uint8_t Hex2Byte(char *src)
> > or even better:
> > Hex2Byte(char *src, byte_idx)
> >    and do pointer arithmetic inside
> >
> > [...]
> > > build_append_byte(var->buf, Hex2Byte(uuid + (3 * 2))); /* dd */
> > build_append_byte(var->buf, Hex2Byte(uuid, 3)); /* dd - at offset 00 */
> > build_append_byte(var->buf, Hex2Byte(uuid, 2)); /* cc - at offset 01 */
> > ...
> Yes, it's better to first four bytes. But there are hyphens /-/, for
> offset 04, 05 and etc it doesn't work. We can't use following expression:
>
> build_append_byte(var->buf, Hex2Byte(uuid, 5)); /* ff - at offset 04 */
> build_append_byte(var->buf, Hex2Byte(uuid, 4)); /* ee - at offset 05 */
> ...

So about the implementation of this macro, I think I'd like to use 
following approach. This lets Hex2Byte do what it should only do and 
still has a clear look of UUID. What do you think about?

static uint8_t Hex2Byte(char *src)
{
    int hi = Hex2Digit(*src++);
    int lo = Hex2Digit(*src);

    if ((hi < 0) || (lo < 0))
        return -1;

    return (hi << 4) | lo;
}

g_assert((strlen(uuid) == 36) && (uuid[8] == '-') && (uuid[13] == '-')
          && (uuid[18] == '-') && (uuid[23] == '-'));

build_append_byte(var->buf, Hex2Byte(uuid + (3 * 2))); /* dd */
build_append_byte(var->buf, Hex2Byte(uuid + (2 * 2))); /* cc */
build_append_byte(var->buf, Hex2Byte(uuid + (1 * 2))); /* bb */
build_append_byte(var->buf, Hex2Byte(uuid + (0 * 2))); /* aa */

build_append_byte(var->buf, Hex2Byte(uuid + (5 * 2 + 1))); /* ff */
build_append_byte(var->buf, Hex2Byte(uuid + (4 * 2 + 1))); /* ee */

build_append_byte(var->buf, Hex2Byte(uuid + (7 * 2 + 2))); /* hh */
build_append_byte(var->buf, Hex2Byte(uuid + (6 * 2 + 2))); /* gg */

build_append_byte(var->buf, Hex2Byte(uuid + (8 * 2 + 3))); /* ii */
build_append_byte(var->buf, Hex2Byte(uuid + (9 * 2 + 3))); /* jj */

build_append_byte(var->buf, Hex2Byte(uuid + (10 * 2 + 4))); /* kk */
build_append_byte(var->buf, Hex2Byte(uuid + (11 * 2 + 4))); /* ll */
build_append_byte(var->buf, Hex2Byte(uuid + (12 * 2 + 4))); /* mm */
build_append_byte(var->buf, Hex2Byte(uuid + (13 * 2 + 4))); /* nn */
build_append_byte(var->buf, Hex2Byte(uuid + (14 * 2 + 4))); /* oo */
build_append_byte(var->buf, Hex2Byte(uuid + (15 * 2 + 4))); /* pp */