`lerp` is `a + (b - a) * f`, and `b - a` is nothing often enough to be worth
asking: a box with the same pixels at both ends of an axis, a span with no
fraction of one, a part of a subtree whose box did not move on that axis.
`Fixed::scaled` is `mul` that answers a zero receiver without widening to
`i64`, rounding and narrowing back, and `lerp` uses it -- so every lerp in
layout gets it rather than the two places that were about to grow their own
comparison.
`many` over 500 frames: 1,705,786,553 instructions to 1,657,571,216, and
638.9M cycles against 657.9M, averaged over four runs each.
Checked: fmt, clippy, 105 tests, all five shrinker cases at 300 seeds, and
`tabs`, `text`, `random`, `minimal` and `view` byte-identical at 1920x1200.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
iris-aiandClaude Opus 5
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