From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:55478 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753981Ab3KNNqA (ORCPT ); Thu, 14 Nov 2013 08:46:00 -0500 Message-ID: <5284D410.4010706@iki.fi> Date: Thu, 14 Nov 2013 15:45:52 +0200 From: Antti Palosaari MIME-Version: 1.0 To: Hans Verkuil , Andy Walls CC: linux-media@vger.kernel.org Subject: Re: [PATCH RFC] libv4lconvert: SDR conversion from U8 to FLOAT References: <1384103776-4788-1-git-send-email-crope@iki.fi> <1384179541.1949.24.camel@palomino.walls.org> <5280EBD4.5010505@xs4all.nl> In-Reply-To: <5280EBD4.5010505@xs4all.nl> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 11.11.2013 16:38, Hans Verkuil wrote: > 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). I want use existing data formats and that [-1 to +1] scaled 32-bit IEEE-754 floating point is de facto format for SDR application (actually pair of floats as a complex). Doing conversion inside libv4lconvert makes it very easy for write application. Currently I have implemented GNU Radio and SDRsharp plugins that feeds data from device via libv4l2 using mmap and conversion. Thanks to pointing endianess issue, I didn't though it all. I suspect those apps just relies to local endianess. So do I have to implement float format conversion with both endianess? > > Regards, > > Hans > >> >> Two more comments below... >> >>> Signed-off-by: Antti Palosaari >>> --- >>> 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). Will do. >> >> >>> + } >>> + } >>> + } >>> + 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 regards Antti -- http://palosaari.fi/