From e388e16e71d2845a9c26979e70e092153ef5a24b Mon Sep 17 00:00:00 2001
From: bloeys <bloeys@outlook.com>
Date: Mon, 1 Aug 2022 07:14:35 +0400
Subject: [PATCH] Use binary search in GetParaFromTextBufIndex

---
 main.go      | 34 ++++++++++++++++++----------------
 ring/ring.go | 11 +++++++++++
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/main.go b/main.go
index e7c171c..a80e22d 100755
--- a/main.go
+++ b/main.go
@@ -1096,13 +1096,10 @@ func GetParaFromTextBufIndex(it ring.Iterator[byte], paraIt ring.Iterator[Para],
 		return
 	}
 
-	ticks := 0
-
-	//Find first valid para
+	// Find first valid para
 	paraIt.GotoStart()
 	for p, done := paraIt.NextPtr(); !done; p, done = paraIt.NextPtr() {
 
-		ticks++
 		if !IsParaValid(it.Buf, p) {
 			continue
 		}
@@ -1111,25 +1108,30 @@ func GetParaFromTextBufIndex(it ring.Iterator[byte], paraIt ring.Iterator[Para],
 		break
 	}
 
-	// @PERF We need a faster way of finding the current paragraph. Binary search?
-	for p, done := paraIt.NextPtr(); !done; p, done = paraIt.NextPtr() {
+	// Binary search for the paragraph
+	lowIndexRel := paraIt.CurrToRelIndex()
+	highIndexRel := uint64(paraIt.Buf.Len)
+	for lowIndexRel <= highIndexRel {
+
+		medianIndexRel := (lowIndexRel + highIndexRel) / 2
+		p := paraIt.Buf.GetPtr(medianIndexRel)
 
-		ticks++
 		startIndexRel := it.Buf.RelIndexFromWriteCount(p.StartIndex_WriteCount)
 		endIndexRel := it.Buf.RelIndexFromWriteCount(p.EndIndex_WriteCount)
-		if textBufStartIndexRel < startIndexRel || textBufStartIndexRel > endIndexRel {
-			continue
-		}
 
-		outPara = p
-		pIndex = paraIt.CurrToRelIndex()
-		break
+		if textBufStartIndexRel < startIndexRel {
+			highIndexRel = medianIndexRel - 1
+		} else if textBufStartIndexRel > endIndexRel {
+			lowIndexRel = medianIndexRel + 1
+		} else {
+			outPara = p
+			pIndex = medianIndexRel
+			break
+		}
 	}
 
-	println("Ticks to finding para:", ticks)
-
 	if outPara == nil {
-		panic("Could not find para")
+		panic(fmt.Sprintf("Could not find paragraph for index %d", textBufStartIndexRel))
 	}
 
 	return outPara, pIndex
diff --git a/ring/ring.go b/ring/ring.go
index 71379af..731e533 100755
--- a/ring/ring.go
+++ b/ring/ring.go
@@ -74,6 +74,17 @@ func (b *Buffer[T]) Get(index uint64) (val T) {
 	return b.Data[(b.Start+int64(index))%b.Cap]
 }
 
+// Get returns the element at the index relative from Buffer.Start
+// If there are no elements then the default value of T is returned
+func (b *Buffer[T]) GetPtr(index uint64) (val *T) {
+
+	if index >= uint64(b.Len) {
+		return new(T)
+	}
+
+	return &b.Data[(b.Start+int64(index))%b.Cap]
+}
+
 // AbsIndexFromRel takes an index relative to Buffer.Start and returns an absolute index into Buffer.Data
 func (b *Buffer[T]) AbsIndexFromRel(relIndex uint64) uint64 {
 	return uint64((b.Start + int64(relIndex)) % b.Cap)