From 447dc2bb9011078e80acbe3f51135ff1ad2bf163 Mon Sep 17 00:00:00 2001
From: Yuri Pieters <magejohnyjtp@gmail.com>
Date: Thu, 9 Apr 2020 01:49:42 +0100
Subject: [PATCH 1/3] sort.binarySearch: fix integer underflow (#4980)

When the key was smaller than any value in the array, an error was
ocurring with the mid being zero and having 1 subtracted from it.
---
 lib/std/sort.zig | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index 3447a0576951..91d29dd22dcc 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -10,16 +10,16 @@ pub fn binarySearch(comptime T: type, key: T, items: []const T, comptime compare
         return null;
 
     var left: usize = 0;
-    var right: usize = items.len - 1;
+    var right: usize = items.len;
 
-    while (left <= right) {
+    while (left < right) {
         // Avoid overflowing in the midpoint calculation
         const mid = left + (right - left) / 2;
         // Compare the key with the midpoint element
         switch (compareFn(key, items[mid])) {
             .eq => return mid,
             .gt => left = mid + 1,
-            .lt => right = mid - 1,
+            .lt => right = mid,
         }
     }
 

From b7e72cc4211d7b06e2b7095f48c579ce1daaf253 Mon Sep 17 00:00:00 2001
From: Yuri Pieters <magejohnyjtp@gmail.com>
Date: Thu, 9 Apr 2020 02:00:08 +0100
Subject: [PATCH 2/3] sort.binarySearch: test for regresson of #4980

---
 lib/std/sort.zig | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index 91d29dd22dcc..c6dcaac49e15 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -47,6 +47,10 @@ test "std.sort.binarySearch" {
         @as(?usize, null),
         binarySearch(u32, 1, &[_]u32{0}, S.order_u32),
     );
+    testing.expectEqual(
+        @as(?usize, null),
+        binarySearch(u32, 0, &[_]u32{1}, S.order_u32),
+    );
     testing.expectEqual(
         @as(?usize, 4),
         binarySearch(u32, 5, &[_]u32{ 1, 2, 3, 4, 5 }, S.order_u32),

From f5f77089b76be2832640884f14c552c49c9fda1f Mon Sep 17 00:00:00 2001
From: Yuri Pieters <magejohnyjtp@gmail.com>
Date: Thu, 9 Apr 2020 09:13:47 +0100
Subject: [PATCH 3/3] sort.binarySearch: Remove unneeded edge case check

---
 lib/std/sort.zig | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/lib/std/sort.zig b/lib/std/sort.zig
index c6dcaac49e15..8ed8f2c1c0ec 100644
--- a/lib/std/sort.zig
+++ b/lib/std/sort.zig
@@ -6,9 +6,6 @@ const math = std.math;
 const builtin = @import("builtin");
 
 pub fn binarySearch(comptime T: type, key: T, items: []const T, comptime compareFn: fn (lhs: T, rhs: T) math.Order) ?usize {
-    if (items.len < 1)
-        return null;
-
     var left: usize = 0;
     var right: usize = items.len;