perf: optimize {Trace,Span}_id.is_zero

src/core/span_id.ml

@@ -11,10 +11,13 @@ let create () : t =
   Bytes.set b 0 (Char.unsafe_chr (Char.code (Bytes.get b 0) lor 1));
   b
 
+(* dark magic, woo. We have an [assert] below to do the bound checks once *)
+external unsafe_b_get64 : bytes -> int -> int64 = "%caml_bytes_get64u"
+
 let[@inline] is_zero (self : t) : bool =
   (* try to reduce branches *)
   assert (Bytes.length self = 8);
-  let n1 = Bytes.get_int64_ne self 0 in
+  let n1 = unsafe_b_get64 self 0 in
   n1 = 0L
 
 let[@inline] is_valid self = not (is_zero self)

src/core/trace_id.ml

@@ -17,11 +17,14 @@ let[@inline] of_bytes b =
   else
     invalid_arg "trace ID must be 16 bytes in length"
 
+(* dark magic, woo. We have an [assert] below to do the bound checks once *)
+external unsafe_b_get64 : bytes -> int -> int64 = "%caml_bytes_get64u"
+
 let[@inline] is_zero (self : t) : bool =
   (* try to reduce branches *)
-  assert (Bytes.length self = 1);
-  let n1 = Bytes.get_int64_ne self 0 in
-  let n2 = Bytes.get_int64_ne self 8 in
+  assert (Bytes.length self = 16);
+  let n1 = unsafe_b_get64 self 0 in
+  let n2 = unsafe_b_get64 self 8 in
   n1 = 0L && n2 = 0L
 
 let[@inline] is_valid self = not (is_zero self)
@@ -37,4 +40,12 @@ let[@inline] of_hex_substring s off =
 
 let pp fmt t = Format.fprintf fmt "%s" (to_hex t)
 
+let compare = Bytes.compare
+
+module Map = Map.Make (struct
+  type nonrec t = t
+
+  let compare = compare
+end)
+
 let k_trace_id : t Hmap.key = Hmap.Key.create ()

src/core/trace_id.mli

@@ -8,6 +8,8 @@ val create : unit -> t
 
 val dummy : t
 
+val compare : t -> t -> int
+
 val pp : Format.formatter -> t -> unit
 
 val is_valid : t -> bool
@@ -24,6 +26,8 @@ val of_hex : string -> t
 
 val of_hex_substring : string -> int -> t
 
+module Map : Map.S with type key = t
+
 val k_trace_id : t Hmap.key
 (** Hmap key to carry around a {!Trace_id.t}, to remember what the current trace
     is.