diff options
Diffstat (limited to 'src/runtime/lfstack_amd64.go')
| -rw-r--r-- | src/runtime/lfstack_amd64.go | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/src/runtime/lfstack_amd64.go b/src/runtime/lfstack_amd64.go index 1245557819..84e28519f6 100644 --- a/src/runtime/lfstack_amd64.go +++ b/src/runtime/lfstack_amd64.go @@ -4,9 +4,21 @@ package runtime -// Amd64 uses 48-bit virtual addresses, 47-th bit is used as kernel/user flag. -// So we use 17msb of pointers as ABA counter. -const ( - lfPtrBits = 47 - lfCountMask = 1<<17 - 1 -) +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 +} |