From 8161583fa12ab8deeb6ab6caf7629ac7c439e3ad Mon Sep 17 00:00:00 2001
From: liyichao <liyichao@bytedance.com>
Date: Thu, 30 Sep 2021 19:38:37 +0800
Subject: [PATCH] feat: add fastrand.Read()

---
 lang/fastrand/fastrand.go      | 27 +++++++++++++++++++++++++++
 lang/fastrand/fastrand_test.go |  3 +++
 2 files changed, 30 insertions(+)

diff --git a/lang/fastrand/fastrand.go b/lang/fastrand/fastrand.go
index 34952e20..153b2371 100644
--- a/lang/fastrand/fastrand.go
+++ b/lang/fastrand/fastrand.go
@@ -16,6 +16,8 @@
 package fastrand
 
 import (
+	"unsafe"
+
 	"github.com/bytedance/gopkg/internal/runtimex"
 )
 
@@ -121,3 +123,28 @@ func Uint32n(n uint32) uint32 {
 func Uint64n(n uint64) uint64 {
 	return Uint64() % n
 }
+
+// Read generates len(p) random bytes and writes them into p.
+// It always returns len(p) and a nil error. And it is safe
+// for concurrent use.
+func Read(p []byte) (n int, err error) {
+	l := len(p)
+
+	if l >= 4 {
+		i := 0
+		uint32p := *(*[]uint32)(unsafe.Pointer(&p))
+		for ; l >= 4; l -= 4 {
+			uint32p[i] = Uint32()
+			i++
+		}
+	}
+
+	if l > 0 {
+		r := Uint32()
+		for ; l > 0; l-- {
+			p[len(p)-l] = byte(r >> (l * 8))
+		}
+	}
+
+	return len(p), nil
+}
diff --git a/lang/fastrand/fastrand_test.go b/lang/fastrand/fastrand_test.go
index 2ca1a971..a8dd121c 100644
--- a/lang/fastrand/fastrand_test.go
+++ b/lang/fastrand/fastrand_test.go
@@ -21,6 +21,9 @@ import (
 
 func TestAll(t *testing.T) {
 	_ = Uint32()
+
+	bytes := make([]byte, 1000)
+	_, _ = Read(bytes)
 }
 
 func BenchmarkSingleCore(b *testing.B) {