linear -> sRGB: use fast approximate sqrt()
Since we're already approximating the sRGB gamma curve with a sqrt(), we might
as well approximate with it a faster approximate sqrt(). On Intel, this
.rsqrt().invert() version is 2-3x faster than .sqrt() (~3x faster on older
machines, ~2x faster on newer machines).
This should provide ~11 bits of precision, suspiciously exactly enough.
Running dm --config srgb, there are diffs, but none perceptible.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2046063002
Review-Url: https://codereview.chromium.org/2046063002
3 files changed