sample: use container/heap for top_k

sample/transforms.go

@@ -1,10 +1,30 @@
 package sample
 
 import (
+	"container/heap"
 	"math"
 	"slices"
 )
 
+// tokenHeap implements heap.Interface and holds tokens as a min-heap to track k largest elements
+type tokenHeap []token
+
+func (h tokenHeap) Len() int           { return len(h) }
+func (h tokenHeap) Less(i, j int) bool { return h[i].value < h[j].value } // Use < for min-heap to track largest elements
+func (h tokenHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *tokenHeap) Push(x any) {
+	*h = append(*h, x.(token))
+}
+
+func (h *tokenHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
 // temperature applies scaling and softmax to the logits
 func temperature(ts []token, temp float32) []token {
 	// Find max logit for numerical stability
@@ -31,62 +51,33 @@ func temperature(ts []token, temp float32) []token {
 	return ts
 }
 
-// siftDown maintains a min-heap property by recursively moving larger elements down the heap.
-//
-// The heap is represented as an array where for any node at index i:
-// - Left child is at index 2i + 1
-// - Right child is at index 2i + 2
-// - Parent is at index (i-1)/2
-//
-// The function compares a node with its children and:
-// 1. Finds the smallest value between the node and its children
-// 2. If the node is not the smallest, swaps it with its smallest child
-// 3. Continues this process down the affected path until the min-heap property is restored
-func siftDown(data []token, start, end int) {
-	root := start
-	for {
-		child := 2*root + 1
-		if child >= end {
-			break
-		}
-		// Find smaller child (we want min heap)
-		if child+1 < end && data[child+1].value < data[child].value {
-			child++
-		}
-		// Exit if root is already smaller than children
-		if data[root].value <= data[child].value {
-			break
-		}
-		// Swap with smaller child and continue
-		data[root], data[child] = data[child], data[root]
-		root = child
-	}
-}
-
 // topK limits the number of tokens considered to the k highest logits
 func topK(ts []token, k int) []token {
 	if k >= len(ts) {
+		sortLogits(ts)
 		return ts
 	}
-	// Heapify + siftDown - O(nlog(k))
-	// Build min-heap of first k elements
-	heap := ts[:k]
-	for i := k/2 - 1; i >= 0; i-- {
-		siftDown(heap, i, k)
-	}
 
-	// Process remaining elements - if larger than heap root, replace root
+	// Initialize min-heap with first k elements
+	h := make(tokenHeap, k)
+	copy(h, ts[:k])
+	heap.Init(&h)
+
+	// Process remaining elements
 	for i := k; i < len(ts); i++ {
-		if ts[i].value > heap[0].value {
-			heap[0] = ts[i]
-			siftDown(heap, 0, k)
+		if ts[i].value > h[0].value {
+			heap.Pop(&h)
+			heap.Push(&h, ts[i])
 		}
 	}
 
-	slices.Reverse(heap)
+	// Convert heap to sorted slice in descending order
+	result := make([]token, k)
+	for i := k - 1; i >= 0; i-- {
+		result[i] = heap.Pop(&h).(token)
+	}
 
-	ts = heap
-	return ts
+	return result
 }
 
 // topP limits tokens to those with cumulative probability p