1 files changed, 24 insertions, 0 deletions
diff --git a/src/runtime/lfstack_amd64.go b/src/runtime/lfstack_amd64.go
new file mode 100644
index 0000000000..84e28519f6
--- /dev/null
+++ b/src/runtime/lfstack_amd64.go
@@ -0,0 +1,24 @@
+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "unsafe"
+
+// On AMD64, virtual addresses are 48-bit numbers sign extended to 64.
+// We shift the address left 16 to eliminate the sign extended part and make
+// room in the bottom for the count.
+// In addition to the 16 bits taken from the top, we can take 3 from the
+// bottom, because node must be pointer-aligned, giving a total of 19 bits
+// of count.
+
+func lfstackPack(node *lfnode, cnt uintptr) uint64 {
+	return uint64(uintptr(unsafe.Pointer(node)))<<16 | uint64(cnt&(1<<19-1))
+}
+
+func lfstackUnpack(val uint64) (node *lfnode, cnt uintptr) {
+	node = (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> 19 << 3)))
+	cnt = uintptr(val & (1<<19 - 1))
+	return
+}