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Consolidate scalar sigmoid onto a shared overflow-safe helper - #317
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DetectionDecoder and SegmentationPostprocessor each defined their own scalar `sigmoid(_:)`. The video decoder's branches on the sign so the exponent argument stays non-positive (overflow-safe); the segmenter's naive `1/(1+exp(-x))` underflows large-negative logits to exactly 0. Add one shared `sigmoid` in CoreAIShared/Runtime/VectorMath.swift (the sign-branched form) and route both subsystems and their tests through it, deleting the two duplicates. VectorMathTests characterizes both extremes. Intended behavior change: the segmenter path now returns a tiny positive value instead of exactly 0 for large-negative logits — negligible for any threshold > 0. WS4 PR2.
stikves
requested review from
alejandro-isaza,
carinapeng,
kevchengcodes and
tjia1818
October 1, 2026 18:14
- Condense the `sigmoid` doc comment and mark it `@inline(__always)` (it runs per-pixel on the detector/segmenter paths). - Delete the `sigmoidKnownValues` (image-segmenter) and `sigmoidStability` (video-segmenter) tests: `VectorMathTests` already covers both the known values and the overflow-safe extremes.
kevchengcodes
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Oct 5, 2026
kevchengcodes
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Looks like you addressed the comments in #320 here. Thanks for doing that, I'll leave it up to you to determine PR merge strategy
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Both
DetectionDecoder(CoreAIVideoSegmenter) andSegmentationPostprocessor(CoreAIImageSegmenter) defined their own scalarsigmoid(_:). The video decoder branches on the sign ofxso the exponent argument stays non-positive (overflow-safe); the segmenter's naive1 / (1 + exp(-x))underflows large-negative logits to exactly0. This folds both onto one sharedsigmoidinCoreAIShared/Runtime/VectorMath.swift(the sign-branched form) and routes both subsystems and their tests through it.Behavior change: the segmenter now returns a tiny positive value instead of
0for large-negative logits, well below any threshold it applies.Adds
VectorMathTestsfor both extremes; the existing segmenter and tracker-score suites were migrated to the shared function and pass.Part of the shared-utility cleanup.