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.
Two more comments below...
> Signed-off-by: Antti Palosaari <cr...@iki.fi>
> ---
> 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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