zig

commit 543031db35ede984b60a00c8f8a7859c6acfebdd (tree)
parent f1360bee1ce6096f1c123347313a7d24a0d90650
Author: Andrew Kelley <andrew@ziglang.org>
Date:   Thu,  9 Apr 2020 14:58:07 -0400

Merge pull request #4982 from MageJohn/fix/binarySearch

 sort.binarySearch: fix integer underflow (#4980) 
Diffstat:
M
lib/std/sort.zig
 | 
13
+++++++------

1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/lib/std/sort.zig b/lib/std/sort.zig
@@ -6,20 +6,17 @@ 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 - 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,
         }
     }
 
@@ -48,6 +45,10 @@ test "std.sort.binarySearch" {
         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),
     );