std: remove loop from growCapacity

I measured this against master branch and found no statistical
difference. Since this code is simpler and logically superior due to
always leaving sufficient unused capacity when growing, it is preferred
over status quo.

lib/std/Io/Writer.zig

@@ -2661,7 +2661,7 @@ pub const Allocating = struct {
     pub fn ensureTotalCapacity(a: *Allocating, new_capacity: usize) Allocator.Error!void {
         // Protects growing unnecessarily since better_capacity will be larger.
         if (a.writer.buffer.len >= new_capacity) return;
-        const better_capacity = ArrayList(u8).growCapacity(a.writer.buffer.len, new_capacity);
+        const better_capacity = ArrayList(u8).growCapacity(new_capacity);
         return ensureTotalCapacityPrecise(a, better_capacity);
     }
 

lib/std/array_list.zig

@@ -172,7 +172,7 @@ pub fn AlignedManaged(comptime T: type, comptime alignment: ?mem.Alignment) type
             // a new buffer and doing our own copy. With a realloc() call,
             // the allocator implementation would pointlessly copy our
             // extra capacity.
-            const new_capacity = Aligned(T, alignment).growCapacity(self.capacity, new_len);
+            const new_capacity = Aligned(T, alignment).growCapacity(new_len);
             const old_memory = self.allocatedSlice();
             if (self.allocator.remap(old_memory, new_capacity)) |new_memory| {
                 self.items.ptr = new_memory.ptr;
@@ -408,7 +408,7 @@ pub fn AlignedManaged(comptime T: type, comptime alignment: ?mem.Alignment) type
             // Protects growing unnecessarily since better_capacity will be larger.
             if (self.capacity >= new_capacity) return;
 
-            const better_capacity = Aligned(T, alignment).growCapacity(self.capacity, new_capacity);
+            const better_capacity = Aligned(T, alignment).growCapacity(new_capacity);
             return self.ensureTotalCapacityPrecise(better_capacity);
         }
 
@@ -1160,7 +1160,7 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
         /// Invalidates element pointers if additional memory is needed.
         pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
             if (self.capacity >= new_capacity) return;
-            return self.ensureTotalCapacityPrecise(gpa, growCapacity(self.capacity, new_capacity));
+            return self.ensureTotalCapacityPrecise(gpa, growCapacity(new_capacity));
         }
 
         /// If the current capacity is less than `new_capacity`, this function will
@@ -1359,17 +1359,12 @@ pub fn Aligned(comptime T: type, comptime alignment: ?mem.Alignment) type {
             return self.getLast();
         }
 
-        const init_capacity = @as(comptime_int, @max(1, std.atomic.cache_line / @sizeOf(T)));
+        const init_capacity: comptime_int = @max(1, std.atomic.cache_line / @sizeOf(T));
 
         /// Called when memory growth is necessary. Returns a capacity larger than
         /// minimum that grows super-linearly.
-        pub fn growCapacity(current: usize, minimum: usize) usize {
+        pub fn growCapacity(minimum: usize) usize {
-            var new = current;
+            return minimum +| (minimum / 2 + init_capacity);
-            while (true) {
-                new +|= new / 2 + init_capacity;
-                if (new >= minimum)
-                    return new;
-            }
         }
     };
 }

lib/std/deque.zig

@@ -56,7 +56,7 @@ pub fn Deque(comptime T: type) type {
         /// Invalidates element pointers if additional memory is needed.
         pub fn ensureTotalCapacity(deque: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
             if (deque.buffer.len >= new_capacity) return;
-            return deque.ensureTotalCapacityPrecise(gpa, growCapacity(deque.buffer.len, new_capacity));
+            return deque.ensureTotalCapacityPrecise(gpa, std.ArrayList(T).growCapacity(new_capacity));
         }
 
         /// If the current capacity is less than `new_capacity`, this function will
@@ -243,18 +243,6 @@ pub fn Deque(comptime T: type) type {
                 return index - head_len;
             }
         }
-
-        const init_capacity: comptime_int = @max(1, std.atomic.cache_line / @sizeOf(T));
-
-        /// Called when memory growth is necessary. Returns a capacity larger than
-        /// minimum that grows super-linearly.
-        fn growCapacity(current: usize, minimum: usize) usize {
-            var new = current;
-            while (true) {
-                new +|= new / 2 + init_capacity;
-                if (new >= minimum) return new;
-            }
-        }
     };
 }
 

lib/std/multi_array_list.zig

@@ -457,24 +457,19 @@ pub fn MultiArrayList(comptime T: type) type {
         /// Invalidates element pointers if additional memory is needed.
         pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
             if (self.capacity >= new_capacity) return;
-            return self.setCapacity(gpa, growCapacity(self.capacity, new_capacity));
+            return self.setCapacity(gpa, growCapacity(new_capacity));
         }
 
-        const init_capacity = init: {
+        const init_capacity: comptime_int = init: {
-            var max = 1;
+            var max: comptime_int = 1;
-            for (fields) |field| max = @as(comptime_int, @max(max, @sizeOf(field.type)));
+            for (fields) |field| max = @max(max, @sizeOf(field.type));
-            break :init @as(comptime_int, @max(1, std.atomic.cache_line / max));
+            break :init @max(1, std.atomic.cache_line / max);
         };
 
-        /// Called when memory growth is necessary. Returns a capacity larger than
+        /// Given a lower bound of required memory capacity, returns a larger value
-        /// minimum that grows super-linearly.
+        /// with super-linear growth.
-        fn growCapacity(current: usize, minimum: usize) usize {
+        pub fn growCapacity(minimum: usize) usize {
-            var new = current;
+            return minimum +| (minimum / 2 + init_capacity);
-            while (true) {
-                new +|= new / 2 + init_capacity;
-                if (new >= minimum)
-                    return new;
-            }
         }
 
         /// Modify the array so that it can hold at least `additional_count` **more** items.