On 11/11/2013 03:19 PM, Andy Walls wrote:
> On Sun, 2013-11-10 at 19:16 +0200, Antti Palosaari wrote:
>> Convert unsigned 8 to float 32 [-1 to +1], which is commonly
>> used format for baseband signals.
>
> Hi Annti,
>
> I don't think this a good idea. Floating point representations are
> inherently non-portable. Even though most everything now uses IEEE-754
> representation, things like denormaliazed numbers may be treated
> differently by different machines. If someone saves the data to a file,
> endianess issues aside, there are no guarantees that a different machine
> reading is going to interpret all the floating point data from that file
> properly.
>
> I really would recommend staying with scaled integer representations or
> explicit integer mantissa, exponent representations.
For what it's worth: ALSA does support float format as well (both LE and BE).
Regards,
Hans
>
> Two more comments below...
>
>> Signed-off-by: Antti Palosaari <[email protected]>
>> ---
>> contrib/freebsd/include/linux/videodev2.h | 4 ++++
>> include/linux/videodev2.h | 4 ++++
>> lib/libv4lconvert/libv4lconvert.c | 29 ++++++++++++++++++++++++++++-
>> 3 files changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/contrib/freebsd/include/linux/videodev2.h
>> b/contrib/freebsd/include/linux/videodev2.h
>> index 1fcfaeb..8829400 100644
>> --- a/contrib/freebsd/include/linux/videodev2.h
>> +++ b/contrib/freebsd/include/linux/videodev2.h
>> @@ -465,6 +465,10 @@ struct v4l2_pix_format {
>> #define V4L2_PIX_FMT_SE401 v4l2_fourcc('S', '4', '0', '1') /* se401
>> janggu compressed rgb */
>> #define V4L2_PIX_FMT_S5C_UYVY_JPG v4l2_fourcc('S', '5', 'C', 'I') /*
>> S5C73M3 interleaved UYVY/JPEG */
>>
>> +/* SDR */
>> +#define V4L2_PIX_FMT_FLOAT v4l2_fourcc('D', 'F', '3', '2') /* float
>> 32-bit */
>> +#define V4L2_PIX_FMT_U8 v4l2_fourcc('D', 'U', '0', '8') /* unsigned
>> 8-bit */
>> +
>> /*
>> * F O R M A T E N U M E R A T I O N
>> */
>> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
>> index 437f1b0..14299a6 100644
>> --- a/include/linux/videodev2.h
>> +++ b/include/linux/videodev2.h
>> @@ -431,6 +431,10 @@ struct v4l2_pix_format {
>> #define V4L2_PIX_FMT_SE401 v4l2_fourcc('S', '4', '0', '1') /* se401
>> janggu compressed rgb */
>> #define V4L2_PIX_FMT_S5C_UYVY_JPG v4l2_fourcc('S', '5', 'C', 'I') /*
>> S5C73M3 interleaved UYVY/JPEG */
>>
>> +/* SDR */
>> +#define V4L2_PIX_FMT_FLOAT v4l2_fourcc('D', 'F', '3', '2') /* float
>> 32-bit */
>> +#define V4L2_PIX_FMT_U8 v4l2_fourcc('D', 'U', '0', '8') /* unsigned
>> 8-bit */
>> +
>> /*
>> * F O R M A T E N U M E R A T I O N
>> */
>> diff --git a/lib/libv4lconvert/libv4lconvert.c
>> b/lib/libv4lconvert/libv4lconvert.c
>> index e2afc27..38c9125 100644
>> --- a/lib/libv4lconvert/libv4lconvert.c
>> +++ b/lib/libv4lconvert/libv4lconvert.c
>> @@ -78,7 +78,8 @@ static void v4lconvert_get_framesizes(struct
>> v4lconvert_data *data,
>> { V4L2_PIX_FMT_RGB24, 24, 1, 5, 0 }, \
>> { V4L2_PIX_FMT_BGR24, 24, 1, 5, 0 }, \
>> { V4L2_PIX_FMT_YUV420, 12, 6, 1, 0 }, \
>> - { V4L2_PIX_FMT_YVU420, 12, 6, 1, 0 }
>> + { V4L2_PIX_FMT_YVU420, 12, 6, 1, 0 }, \
>> + { V4L2_PIX_FMT_FLOAT, 0, 0, 0, 0 }
>>
>> static const struct v4lconvert_pixfmt supported_src_pixfmts[] = {
>> SUPPORTED_DST_PIXFMTS,
>> @@ -131,6 +132,8 @@ static const struct v4lconvert_pixfmt
>> supported_src_pixfmts[] = {
>> { V4L2_PIX_FMT_Y6, 8, 20, 20, 0 },
>> { V4L2_PIX_FMT_Y10BPACK, 10, 20, 20, 0 },
>> { V4L2_PIX_FMT_Y16, 16, 20, 20, 0 },
>> + /* SDR formats */
>> + { V4L2_PIX_FMT_U8, 0, 0, 0, 0 },
>> };
>>
>> static const struct v4lconvert_pixfmt supported_dst_pixfmts[] = {
>> @@ -1281,6 +1284,25 @@ static int v4lconvert_convert_pixfmt(struct
>> v4lconvert_data *data,
>> }
>> break;
>>
>> + /* SDR */
>> + case V4L2_PIX_FMT_U8:
>> + switch (dest_pix_fmt) {
>> + case V4L2_PIX_FMT_FLOAT:
>> + {
>> + /* 8-bit unsigned to 32-bit float */
>> + unsigned int i;
>> + float ftmp;
>> + for (i = 0; i < src_size; i++) {
>> + ftmp = *src++;
>> + ftmp -= 127.5;
>> + ftmp /= 127.5;
>> + memcpy(dest, &ftmp, 4);
>> + dest += 4;
>
> Replace the 4's with sizeof(float).
>
> You have no guarantees that sizeof(float) == 4, but it is usally a safe
> assumption for 'float' on Unix.
>
> sizeof(long double) is certainly different for IA32 machines (80 bits)
> vs. other 32 bit platforms. I was burned by this many years ago on a
> RedHat 9.0 machine (the GNU Ada Translator's libm bindings made some bad
> assumptions about the size of float types).
>
>
>> + }
>> + }
>> + }
>> + break;
>> +
>> default:
>> V4LCONVERT_ERR("Unknown src format in conversion\n");
>> errno = EINVAL;
>> @@ -1349,6 +1371,11 @@ int v4lconvert_convert(struct v4lconvert_data *data,
>> temp_needed =
>> my_src_fmt.fmt.pix.width * my_src_fmt.fmt.pix.height *
>> 3 / 2;
>> break;
>> + /* SDR */
>> + case V4L2_PIX_FMT_FLOAT:
>> + dest_needed = src_size * 4; /* 8-bit to 32-bit */
>
> Change the 4 to sizeof(float).
>
>> + temp_needed = dest_needed;
>> + break;
>> default:
>> V4LCONVERT_ERR("Unknown dest format in conversion\n");
>> errno = EINVAL;
>
> Regards,
> Andy
>
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