From 97b0288365c5cb4da1c0e5714ce7d5a0c4cd752e Mon Sep 17 00:00:00 2001
From: Jonathan Hallstrom <lmj.hallstrom@gmail.com>
Date: Sun, 15 Sep 2024 13:28:33 +0200
Subject: [PATCH] make partitionPoint faster by making it branchless

---
 lib/std/sort.zig | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index 23707f138591..14ce4dde00d9 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -678,18 +678,23 @@ pub fn partitionPoint(
     context: anytype,
     comptime predicate: fn (@TypeOf(context), T) bool,
 ) usize {
-    var low: usize = 0;
-    var high: usize = items.len;
+    var it: usize = 0;
+    var len: usize = items.len;
 
-    while (low < high) {
-        const mid = low + (high - low) / 2;
-        if (predicate(context, items[mid])) {
-            low = mid + 1;
-        } else {
-            high = mid;
+    while (len > 1) {
+        const half: usize = len / 2;
+        len -= half;
+        if (predicate(context, items[it + half - 1])) {
+            @branchHint(.unpredictable);
+            it += half;
         }
     }
-    return low;
+
+    if (it < items.len) {
+        it += @intFromBool(predicate(context, items[it]));
+    }
+
+    return it;
 }
 
 test partitionPoint {