rsc.io/go@v0.0.0-20150416155037-e040fd465409/src/runtime/lfstack_amd64.go (about)

     1  // Copyright 2014 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import "unsafe"
     8  
     9  // On AMD64, virtual addresses are 48-bit numbers sign extended to 64.
    10  // We shift the address left 16 to eliminate the sign extended part and make
    11  // room in the bottom for the count.
    12  // In addition to the 16 bits taken from the top, we can take 3 from the
    13  // bottom, because node must be pointer-aligned, giving a total of 19 bits
    14  // of count.
    15  
    16  func lfstackPack(node *lfnode, cnt uintptr) uint64 {
    17  	return uint64(uintptr(unsafe.Pointer(node)))<<16 | uint64(cnt&(1<<19-1))
    18  }
    19  
    20  func lfstackUnpack(val uint64) (node *lfnode, cnt uintptr) {
    21  	node = (*lfnode)(unsafe.Pointer(uintptr(int64(val) >> 19 << 3)))
    22  	cnt = uintptr(val & (1<<19 - 1))
    23  	return
    24  }