From 6880e404d2810046ede54bb5e19c53bb623af17d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20B=C3=BCnzli?= <daniel.buenzli@erratique.ch>
Date: Wed, 25 Sep 2024 17:14:02 +0200
Subject: [PATCH] Tweak Uuidm.v4_ns (#14).

---
 CHANGES.md         |  5 +++--
 src/uuidm.ml       | 34 +++++++++++++++++-----------------
 src/uuidm.mli      | 42 ++++++++++++++++++++----------------------
 test/test_uuidm.ml |  2 +-
 4 files changed, 41 insertions(+), 42 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index 47e4815..111f6a3 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,7 @@
 
-- Add `Uuidm.v7`, create time and random based V7 UUIDs using client provided
-  random bytes and time. Thanks to Robin Newton for the patch (#14).
+- Add `Uuidm.{v7,v7_ns}` to create time and random based V7 UUIDs. 
+  Thanks to Robin Newton for the patch (#14) and Christian Linding
+  and Pau Ruiz Safont for the help.
 - Add `Uuidm.v8` to create V8 custom UUIDs.
 - Add `Uuidm.max` the RFC 9569 Max UUID.
 - Add `Uuidm.{variant,version,time_ms}` UUID property accessors.
diff --git a/src/uuidm.ml b/src/uuidm.ml
index bc8f5a4..d8d0183 100644
--- a/src/uuidm.ml
+++ b/src/uuidm.ml
@@ -5,7 +5,7 @@
 
 (* Bits *)
 
-type bits48 = int64
+type bits62 = int64
 type bits4 = int
 type bits12 = int
 
@@ -129,23 +129,23 @@ let v7 ~t_ms ~rand_a ~rand_b =
   Bytes.set_int64_be u 8 rand_b;
   make u ~version:7
 
-let v7_ns =
-  let open Int64 in
+let v7_ns ~t_ns ~rand_b =
   let ns_in_ms = 1_000_000L in
-  let sub_ms_frac_multiplier = unsigned_div minus_one ns_in_ms in
-  fun ~t_ns:ts ~rand_b:b ->
-    let u = Bytes.create 16 in
-    Bytes.blit b 0 u 8 8;
-    (* RFC9562 requires we use 48 bits for a timestamp in milliseconds, and
-       allows for 12 bits to store a sub-millisecond fraction. We get the
-       latter by multiplying to put the fraction in a 64-bit range, then
-       shifting into 12 bits. *)
-    let ms = unsigned_div ts ns_in_ms in
-    let ns = unsigned_rem ts ns_in_ms in
-    let sub_ms_frac = shift_right_logical (mul ns sub_ms_frac_multiplier) 52 in
-    Bytes.set_int64_be u 0 (shift_left ms 16);
-    Bytes.set_int16_be u 6 (to_int sub_ms_frac);
-    make u ~version:7
+  let sub_ms_frac_multiplier = Int64.unsigned_div Int64.minus_one ns_in_ms in
+  let u = Bytes.create 16 in
+  (* RFC 9562 requires we use 48 bits for a timestamp in milliseconds, and
+     allows for 12 bits to store a sub-millisecond fraction. We get the
+     latter by multiplying to put the fraction in a 64-bit range, then
+     shifting into 12 bits. *)
+  let ms = Int64.unsigned_div t_ns ns_in_ms in
+  let ns = Int64.unsigned_rem t_ns ns_in_ms in
+  let sub_ms_frac =
+    Int64.shift_right_logical (Int64.mul ns sub_ms_frac_multiplier) 52
+  in
+  Bytes.set_int64_be u 0 (Int64.shift_left ms 16);
+  Bytes.set_int16_be u 6 (Int64.to_int sub_ms_frac);
+  Bytes.set_int64_be u 8 rand_b;
+  make u ~version:7
 
 let v8 s = make (Bytes.of_string s) ~version:8
 
diff --git a/src/uuidm.mli b/src/uuidm.mli
index e39168e..5b0e12f 100644
--- a/src/uuidm.mli
+++ b/src/uuidm.mli
@@ -14,10 +14,6 @@
 
 (** {1:bits Bits} *)
 
-type bits48 = int64
-(** The type for 48 bits stored in the 48 lower bits of an [int64] value.
-    The higher bits are either set to zero or ignored on use. *)
-
 type bits4 = int
 (** The type for 4 bits stored in the 4 lower bits of an [int] value.
     The higher bits are either set to zero or ignored on use. *)
@@ -26,6 +22,10 @@ type bits12 = int
 (** The type for 12 bits stored in the 12 lower bits of an [int] value.
     The higher bits are either set to zero or ignored on use. *)
 
+type bits62 = int64
+(** The type for 62 bits stored in the 62 lower bits of an [int64] value.
+    The higher bits are either set to zero or ignored on use. *)
+
 (** {1:uuids UUIDs} *)
 
 type t
@@ -49,26 +49,24 @@ val v5 : t -> string -> t
     (name based with SHA-1 hashing) named by [n] and
     namespaced by [ns]. *)
 
-val v7 : t_ms:bits48 -> rand_a:bits12 -> rand_b:int64 -> t
+val v7 : t_ms:int64 -> rand_a:bits12 -> rand_b:bits62 -> t
 (** [v7 t_ms ~rand_a ~rand_b] is a
     {{:https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-7}V7 UUID}
-    (time and random based) using the millisecond POSIX timestamp [t_ms] and
-    random bits [rand_a] and [rand_b].
+    (time and random based) using the 64-bit millisecond POSIX timestamp
+    [t_ms] and random bits [rand_a] and [rand_b].
 
-    {b Warning.} The timestamp and the randomness is seen literally
+    {b Warning.} The timestamp and the randomness are seen literally
     in the result. *)
 
-val v7_ns : t_ns:bits48 -> rand_b:bytes -> t
-(** [v7_ns ts b] is a
-    {{:https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-7}V7 UUID}
-    (time and random based) that uses the
-    62 lower bits of [b] for randomness and takes [ts] to be the
-    {e unsigned} number of nanoseconds since midnight 1 Jan 1970 UTC, leap
-    seconds excluded. The timestamp will be represented in the UUID -
-    with a resolution of about 244 nanoseconds - such that the
-    ordering of UUIDs will match the ordering of timestamps.
-
-    {b Warning.} The timestamp and the randomness is seen literally in
+val v7_ns : t_ns:int64 -> rand_b:bits62 -> t
+(** [v7_ns ~ts_ns ~rand_b] is a
+    {{:https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-7}V7
+    UUID} (time and random based) using the {e unsigned} 64-bit
+    nanosecond POSIX timestamp [t_ns] and random bits [rand_b]. The
+    [rand_a] field is used with the timestamp's submilisecond (about
+    244 nanoseconds resolution).
+
+    {b Warning.} The timestamp and the randomness are seen literally in
     the result. *)
 
 val v8 : string -> t
@@ -131,11 +129,11 @@ val version : t -> bits4
     {{:https://www.rfc-editor.org/rfc/rfc9562#name-version-field}version field}
     of [u]. *)
 
-val time_ms : t -> bits48 option
+val time_ms : t -> int64 option
 (** [time_ms u] is the
     {{:https://www.rfc-editor.org/rfc/rfc9562#name-uuid-version-7}
-    [unit_ts_ms]} POSIX timestamp of [u]. This is [None] if [u]
-    is not a V7 UUID. *)
+    [unit_ts_ms]} millisecond POSIX timestamp of [u] as a 64-bit
+    integer. This is [None] if [u] is not a V7 UUID. *)
 
 (** {1:preds Predicates and comparisons} *)
 
diff --git a/test/test_uuidm.ml b/test/test_uuidm.ml
index 2a8c7d3..89f9c92 100644
--- a/test/test_uuidm.ml
+++ b/test/test_uuidm.ml
@@ -46,7 +46,7 @@ let test_constructors () =
 	  "2ed6657d-e927-568b-95e1-2665a8aea6a2";
   test_uuid ~__POS__ 7 ~time_ms:0x1020_3040_5060L
     (Uuidm.v7_ns ~t_ns:Int64.(add (mul 1_000_000L 0x1020_3040_5060L) 213135L)
-       ~rand_b:(Bytes.of_string "\x12\x34\x56\x78\x9a\xbc\xde\xf0"))
+       ~rand_b:0x123456789abcdef0L)
     "10203040-5060-7369-9234-56789abcdef0";
   test_uuid ~__POS__ 7 ~time_ms:0x017F22E279B0L
     (Uuidm.v7