On Fri, Jul 11, 2014 at 12:14:29AM +0100, Ben Avison wrote: > The previous implementation targeted DTS Coherent Acoustics, which only > requires nbits == 4 (fft16()). This case was (and still is) linked directly > rather than being indirected through ff_fft_calc_vfp(), but now the full > range from radix-4 up to radix-65536 is available. This benefits other codecs > such as AAC and AC3. > > The implementaion is based upon the C version, with each routine larger than > radix-16 calling a hierarchy of smaller FFT functions, then performing a > post-processing pass. This pass benefits a lot from loop unrolling to > counter the long pipelines in the VFP. A relaxed calling standard also > reduces the overhead of the call hierarchy, and avoiding the excessive > inlining performed by GCC probably helps with I-cache utilisation too. > > I benchmarked the result by measuring the number of gperftools samples that > hit anywhere in the AAC decoder (starting from aac_decode_frame()) or > specifically in the FFT routines (fft4() to fft512() and pass()) for the > same sample AAC stream: > > Before After > Mean StdDev Mean StdDev Confidence Change > Audio decode 2245.5 53.1 1599.6 43.8 100.0% +40.4% > FFT routines 940.6 22.0 348.1 20.8 100.0% +170.2% > --- > libavcodec/arm/fft_init_arm.c | 8 +- > libavcodec/arm/fft_vfp.S | 261 > ++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 252 insertions(+), 17 deletions(-)
it seems this fails to build ./configure --cross-prefix=/usr/arm-linux-gnueabi/bin/ --cc='ccache arm-linux-gnueabi-gcc-4.5' --extra-cflags='-mfpu=neon -mfloat-abi=softfp' --cpu=cortex-a8 --arch=armv7 --target-os=linux --enable-cross-compile && make -j12 AS libavcodec/arm/fft_vfp.o ffmpeg/libavcodec/arm/fft_vfp.S: Assembler messages: ffmpeg/libavcodec/arm/fft_vfp.S:512: Error: cannot use register index with PC-relative addressing -- `ldr ip,[pc,ip,lsl#2]' make: *** [libavcodec/arm/fft_vfp.o] Error 1 [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB The educated differ from the uneducated as much as the living from the dead. -- Aristotle
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