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image-rs / jpeg-decoder

JPEG decoder written in Rust
Apache License 2.0
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Make small perf refactors, clippy and grammar fixes #165

Closed okaneco closed 4 years ago

okaneco commented 4 years ago

I found some places for improvement based on clippy and experimentation. The benchmarks seemed a bit noisy from run to run. Overall, I believe I had more small performance gains than regressions on my computer but that may not replicate.

decoder.rs
Refactor spectral selection difference magnitude to remove error check from non-zero match arm, better matches table F.1 on page 89 of the document, 93 of the PDF Remove unnecessary closure Return from clamp_to_u8 by expression instead of let value huffman.rs
Avoid collecting in huffsize fold idct.rs
Remove return parser.rs
Use mutable iterator instead of for loop upsampler.rs
Use copy_from_slice instead of for loop

decode a 512x512 JPEG
    time:   [4.1549 ms 4.1638 ms 4.1733 ms]
    change: [-4.6042% -4.1612% -3.7614%] (p = 0.00 < 0.05)
    Performance has improved.

decode a 512x512 progressive JPEG
    time:   [7.6885 ms 7.7178 ms 7.7545 ms]
    change: [-0.7646% -0.2729% +0.3227%] (p = 0.34 > 0.05)
    No change in performance detected.

Benchmarking decode a 512x512 grayscale JPEG
    time:   [1.1805 ms 1.1842 ms 1.1880 ms]
    change: [+0.4658% +0.9305% +1.3867%] (p = 0.00 < 0.05)
    Change within noise threshold.

Benchmarking extract metadata from an imag
    time:   [1.3026 us 1.3054 us 1.3085 us]
    change: [-4.5689% -4.2494% -3.8972%] (p = 0.00 < 0.05)
    Performance has improved.