From 7018ea1399d452ba7fb78cfacbcba2e283cbef8f Mon Sep 17 00:00:00 2001
From: ok32 <e.starikoff@gmail.com>
Date: Fri, 16 May 2025 14:26:13 +0400
Subject: [PATCH] v2: take only 'bitsMachine' least significant bits from
 generated machine IDs so it doesn't corrupt the other ID parts

---
 v2/sonyflake.go      |  4 ++--
 v2/sonyflake_test.go | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/v2/sonyflake.go b/v2/sonyflake.go
index 244e1dd..758b899 100644
--- a/v2/sonyflake.go
+++ b/v2/sonyflake.go
@@ -209,7 +209,7 @@ func (sf *Sonyflake) toID() (int64, error) {
 
 	return sf.elapsedTime<<(sf.bitsSequence+sf.bitsMachine) |
 		int64(sf.sequence)<<sf.bitsMachine |
-		int64(sf.machine), nil
+		(int64(sf.machine) & ((1 << sf.bitsMachine) - 1)), nil
 }
 
 func privateIPv4(interfaceAddrs types.InterfaceAddrs) (net.IP, error) {
@@ -260,7 +260,7 @@ func (sf *Sonyflake) Compose(t time.Time, sequence, machineID int) int64 {
 	elapsedTime := sf.toInternalTime(t.UTC()) - sf.startTime
 	return elapsedTime<<(sf.bitsSequence+sf.bitsMachine) |
 		int64(sequence)<<sf.bitsMachine |
-		int64(machineID)
+		(int64(machineID) & ((1 << sf.bitsMachine) - 1))
 }
 
 // Decompose returns a set of Sonyflake ID parts.
diff --git a/v2/sonyflake_test.go b/v2/sonyflake_test.go
index 30d97b0..9bb7cfe 100644
--- a/v2/sonyflake_test.go
+++ b/v2/sonyflake_test.go
@@ -3,6 +3,7 @@ package sonyflake
 import (
 	"errors"
 	"fmt"
+	"math"
 	"net"
 	"runtime"
 	"testing"
@@ -419,3 +420,28 @@ func TestComposeAndDecompose(t *testing.T) {
 		})
 	}
 }
+
+func TestBigMachineDoesntBreakID(t *testing.T) {
+	start := time.Now()
+	sf := newSonyflake(t, Settings{
+		TimeUnit:  time.Millisecond,
+		StartTime: start,
+		MachineID: func() (int, error) {
+			return math.MaxInt, nil
+		},
+	})
+
+	id := nextID(t, sf)
+	parts := sf.Decompose(id)
+
+	if parts["sequence"] != 0 {
+		t.Errorf("next id sequence mismatch: got %d, want %d", parts["sequence"], 0)
+	}
+
+	id = sf.Compose(time.Now(), 0, math.MaxInt)
+	parts = sf.Decompose(id)
+
+	if parts["sequence"] != 0 {
+		t.Errorf("decompose sequence mismatch: got %d, want %d", parts["sequence"], 0)
+	}
+}