2 files changed, 89 insertions, 0 deletions
diff --git a/src/main.zig b/src/main.zig
new file mode 100644
index 0000000..d5d8c78
--- /dev/null
+++ b/src/main.zig
@@ -0,0 +1,6 @@
+const ma = @import("max_allocator.zig");
+pub const MaxAllocator = ma.MaxAllocator;
+pub const maxAllocator = ma.maxAllocator;
+test {
+    _ = ma;
+}
diff --git a/src/max_allocator.zig b/src/max_allocator.zig
new file mode 100644
index 0000000..00b8630
--- /dev/null
+++ b/src/max_allocator.zig
@@ -0,0 +1,83 @@
+const std = @import("std");
+
+// Wrapper allocator that counts what the largest amount allocated at any time was from backing_allocator.
+pub const MaxAllocator = struct {
+    backing_allocator: std.mem.Allocator,
+    currently_allocated: usize = 0,
+    max_allocated: usize = 0,
+
+    pub fn allocator(self: *@This()) std.mem.Allocator {
+        return std.mem.Allocator{
+            .ptr = self,
+            .vtable = &.{
+                .alloc = rawAlloc,
+                .resize = rawResize,
+                .free = rawFree,
+            },
+        };
+    }
+
+    fn rawAlloc(ctx: *anyopaque, len: usize, ptr_align: u8, ret_addr: usize) ?[*]u8 {
+        var self: *@This() = @alignCast(@ptrCast(ctx));
+        var res = self.backing_allocator.rawAlloc(len, ptr_align, ret_addr);
+        if (res != null) {
+            self.currently_allocated += len;
+            std.log.warn("+{}", .{len});
+            self.max_allocated = @max(self.currently_allocated, self.max_allocated);
+        }
+        return res;
+    }
+
+    fn rawResize(ctx: *anyopaque, buf: []u8, buf_align: u8, new_len: usize, ret_addr: usize) bool {
+        var self: *@This() = @alignCast(@ptrCast(ctx));
+        const res = self.backing_allocator.rawResize(buf, buf_align, new_len, ret_addr);
+        if (res) {
+            self.currently_allocated -= buf.len;
+            std.log.warn("-{}", .{buf.len});
+            self.currently_allocated += new_len;
+            std.log.warn("+{}", .{new_len});
+            self.max_allocated = @max(self.currently_allocated, self.max_allocated);
+        }
+        return res;
+    }
+
+    fn rawFree(ctx: *anyopaque, buf: []u8, buf_align: u8, ret_addr: usize) void {
+        var self: *@This() = @alignCast(@ptrCast(ctx));
+        self.backing_allocator.rawFree(buf, buf_align, ret_addr);
+        self.currently_allocated -= buf.len;
+        std.log.warn("-{}", .{buf.len});
+    }
+};
+
+pub fn maxAllocator(backing_allocator: std.mem.Allocator) MaxAllocator {
+    return MaxAllocator{ .backing_allocator = backing_allocator };
+}
+
+test {
+    const buflen = 2048;
+    var buf = [_]u8{0} ** buflen;
+    var fba = std.heap.FixedBufferAllocator.init(&buf);
+    var ma = maxAllocator(fba.allocator());
+    var a = ma.allocator();
+    var x = try a.alloc(u8, 100);
+    try std.testing.expectEqual(@as(usize, 100), ma.max_allocated);
+    try std.testing.expectEqual(@as(usize, 100), ma.currently_allocated);
+    var y = try a.alloc(u8, 10);
+    try std.testing.expectEqual(@as(usize, 110), ma.max_allocated);
+    try std.testing.expectEqual(@as(usize, 110), ma.currently_allocated);
+    a.free(x);
+    var z = try a.alloc(u8, 50);
+    try std.testing.expectEqual(@as(usize, 110), ma.max_allocated);
+    try std.testing.expectEqual(@as(usize, 60), ma.currently_allocated);
+
+    try std.testing.expect(a.resize(z, 1024));
+    try std.testing.expectEqual(@as(usize, 1034), ma.max_allocated);
+    try std.testing.expectEqual(@as(usize, 1034), ma.currently_allocated);
+
+    a.free(y);
+    a.free(z);
+
+    try std.testing.expectEqual(@as(usize, 1034), ma.max_allocated);
+    try std.testing.expectEqual(@as(usize, 0), ma.currently_allocated); // works on aarch64, not on x86_64 :thinking-face:
+    try std.testing.expectEqual(@as(usize, 0), fba.end_index);
+}