• Ben Avison's avatar
    armv6: Accelerate ff_fft_calc for general case (nbits != 4) · 87552d54
    Ben Avison authored
    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%
    Signed-off-by: 's avatarMartin Storsjö <martin@martin.st>
    87552d54
fft_init_arm.c 2.24 KB