Nico Weber 9875ce0c78 LibPDF: Reorder loops in SampledFunction::evaluate() ...

Previously, we'd loop over the index of the output coordinate,
for example for a CMYK->RGB function, we'd loop over RGB. For
every output index, we'd then sample the function at the CMYK
input point.

Now, we sample at CMYK once and return a span for all outputs,
since they're stored in contiguous memory. And we then loop
over the outputs only to do weighting and mapping to the target
range at the end.

Reduces the runtime of

      (cd Tests/LibPDF; \
          ../../Build/lagom/bin/BenchmarkPDF --benchmark_repetitions 5)

from 235.6±2.3ms to 103.2±3.3ms on my system, and makes
SampledFunction::evaluate() more similar to lerp_nd() in TagTypes.h.

2024-02-13 19:45:19 +01:00

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