subtle package

5 files changed, 45 insertions, 3 deletions

diff --git a/go.mod b/go.mod
index 9c472c0..2879915 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
-module snix.ir/rabbitio
+module rabbitio
 
-go 1.17
+go 1.18
+
+require snix.ir/rabbitio v0.0.0-20220730143105-e697fd436cab
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..290f6e5
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+snix.ir/rabbitio v0.0.0-20220730143105-e697fd436cab h1:Bvqk4nRrgrzZ8m+MNUzUzPUeGTbM+I/e4denc2Cmk5U=
+snix.ir/rabbitio v0.0.0-20220730143105-e697fd436cab/go.mod h1:fGdJrOtVK0uqEI8x6SBI/NPAAQmtQi/4sjwQPShasEA=
diff --git a/rabbit.go b/rabbit.go
index 3d77daa..fe88c92 100644
--- a/rabbit.go
+++ b/rabbit.go
@@ -5,6 +5,8 @@ import (
 	"encoding/binary"
 	"errors"
 	"math/bits"
+
+	"rabbitio/subtle"
 )
 
 const (
@@ -141,7 +143,7 @@ func (r *rabbitCipher) XORKeyStream(dst, src []byte) {
 		panic("rabbitio: output smaller than input")
 	}
 
-	if InexactOverlap(dst, src) {
+	if subtle.InexactOverlap(dst, src) {
 		panic("rabbitio: invalid buffer memory overlap")
 	}
 
diff --git a/subtle/overlap.go b/subtle/overlap.go
new file mode 100644
index 0000000..82ab250
--- /dev/null
+++ b/subtle/overlap.go
@@ -0,0 +1,18 @@
+//go:build !purego
+
+package subtle
+
+import "unsafe"
+
+func AnyOverlap(x, y []byte) bool {
+	return len(x) > 0 && len(y) > 0 &&
+		uintptr(unsafe.Pointer(&x[0])) <= uintptr(unsafe.Pointer(&y[len(y)-1])) &&
+		uintptr(unsafe.Pointer(&y[0])) <= uintptr(unsafe.Pointer(&x[len(x)-1]))
+}
+
+func InexactOverlap(x, y []byte) bool {
+	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
+		return false
+	}
+	return AnyOverlap(x, y)
+}
diff --git a/subtle/purelap.go b/subtle/purelap.go
new file mode 100644
index 0000000..e983129
--- /dev/null
+++ b/subtle/purelap.go
@@ -0,0 +1,18 @@
+//go:build purego
+
+package subtle
+
+import "reflect"
+
+func AnyOverlap(x, y []byte) bool {
+	return len(x) > 0 && len(y) > 0 &&
+		reflect.ValueOf(&x[0]).Pointer() <= reflect.ValueOf(&y[len(y)-1]).Pointer() &&
+		reflect.ValueOf(&y[0]).Pointer() <= reflect.ValueOf(&x[len(x)-1]).Pointer()
+}
+
+func InexactOverlap(x, y []byte) bool {
+	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
+		return false
+	}
+	return AnyOverlap(x, y)
+}