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js/src/softmax.ts

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+/**
+ * Numerically stable softmax + argmax-with-confidence.
+ *
+ * Pure JS — no ORT, no DOM. The classifier ONNX emits raw logits
+ * because softmax-inside-graph would erase the per-class info we
+ * use to surface ``confidence`` to downstream callers.
+ */
+
+/** Argmax + softmax probability of the winning class. Numerically
+ * stable (subtract max before exp). */
+export function argmaxWithProb(
+  logits: Float32Array | number[],
+): { idx: number; prob: number } {
+  let maxLogit = -Infinity;
+  let argmax = 0;
+  for (let i = 0; i < logits.length; i++) {
+    if (logits[i] > maxLogit) {
+      maxLogit = logits[i];
+      argmax = i;
+    }
+  }
+  let z = 0;
+  for (let i = 0; i < logits.length; i++) {
+    z += Math.exp(logits[i] - maxLogit);
+  }
+  return { idx: argmax, prob: 1 / z };
+}