From 29a4ee4d888ccb049df9b50a57e3884ce2d4d0f3 Mon Sep 17 00:00:00 2001
From: Karsten Schmidt <k@postspectacular.com>
Date: Tue, 25 Aug 2020 10:59:26 +0100
Subject: [PATCH] feat(arrays): add non-recursive binary search fns

- add fixed size binarySearch4/8/16/32()
---
 packages/arrays/src/binary-search.ts | 58 ++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/packages/arrays/src/binary-search.ts b/packages/arrays/src/binary-search.ts
index 0846057c26..6e395b0783 100644
--- a/packages/arrays/src/binary-search.ts
+++ b/packages/arrays/src/binary-search.ts
@@ -86,6 +86,64 @@ export const binarySearchNumeric = (
     return -low - 1;
 };
 
+/**
+ * Non-recursive, optimized binary search for fixed size numeric arrays of 4
+ * values. Returns index of `x` or `-index-1` if not found.
+ *
+ * @param buf
+ * @param x
+ */
+export const binarySearch4 = (buf: ArrayLike<number>, x: number) => {
+    let idx = buf[2] <= x ? 2 : 0;
+    idx |= buf[idx + 1] <= x ? 1 : 0;
+    return buf[idx] === x ? idx : -idx - 1;
+};
+
+/**
+ * Non-recursive, optimized binary search for fixed size numeric arrays of 8
+ * values. Returns index of `x` or `-index-1` if not found.
+ *
+ * @param buf
+ * @param x
+ */
+export const binarySearch8 = (buf: ArrayLike<number>, x: number) => {
+    let idx = buf[4] <= x ? 4 : 0;
+    idx |= buf[idx + 2] <= x ? 2 : 0;
+    idx |= buf[idx + 1] <= x ? 1 : 0;
+    return buf[idx] === x ? idx : -idx - 1;
+};
+
+/**
+ * Non-recursive, optimized binary search for fixed size numeric arrays of 16
+ * values. Returns index of `x` or `-index-1` if not found.
+ *
+ * @param buf
+ * @param x
+ */
+export const binarySearch16 = (buf: ArrayLike<number>, x: number) => {
+    let idx = buf[8] <= x ? 8 : 0;
+    idx |= buf[idx + 4] <= x ? 4 : 0;
+    idx |= buf[idx + 2] <= x ? 2 : 0;
+    idx |= buf[idx + 1] <= x ? 1 : 0;
+    return buf[idx] === x ? idx : -idx - 1;
+};
+
+/**
+ * Non-recursive, optimized binary search for fixed size numeric arrays of 32
+ * values. Returns index of `x` or `-index-1` if not found.
+ *
+ * @param buf
+ * @param x
+ */
+export const binarySearch32 = (buf: ArrayLike<number>, x: number) => {
+    let idx = buf[16] <= x ? 16 : 0;
+    idx |= buf[idx + 4] <= x ? 8 : 0;
+    idx |= buf[idx + 4] <= x ? 4 : 0;
+    idx |= buf[idx + 2] <= x ? 2 : 0;
+    idx |= buf[idx + 1] <= x ? 1 : 0;
+    return buf[idx] === x ? idx : -idx - 1;
+};
+
 /**
  * {@link binarySearch} result index classifier for predecessor queries.
  * Returns index of last item less than search value or -1 if no such