On Fri, 11 Jul 2014, Ben Avison wrote:
The previous implementation targeted DTS Coherent Acoustics, which only requires mdct_bits == 6. This relatively small size lent itself to unrolling the loops a small number of times, and encoding offsets calculated at assembly time within the load/store instructions of each iteration.In the more general case (codecs such as AAC and AC3) much larger arrays are used - mdct_bits == [8, 9, 11]. The old method does not scale for these cases, so more integer registers are used with non-unrolled versions of the loops (and with some stack spillage). The postrotation filter loop is still unrolled by a factor of 2 to permit the double-buffering of some VFP registers to facilitate overlap of neighbouring iterations. 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 ff_imdct_half_c / ff_imdct_half_vfp, for the same example AAC stream: Before After Mean StdDev Mean StdDev Confidence Change aac_decode_frame 2368.1 35.8 2117.2 35.3 100.0% +11.8% ff_imdct_half_* 457.5 22.4 251.2 16.2 100.0% +82.1% --- libavcodec/arm/mdct_vfp.S | 146 ++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 144 insertions(+), 2 deletions(-)
Seems ok to me as well (builds well etc) although I don't know the code in detail.
// Martin _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
