mirror of
https://github.com/golang/go
synced 2024-11-23 00:30:07 -07:00
67 lines
1.6 KiB
C
67 lines
1.6 KiB
C
// Copyright 2009 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.
|
|
|
|
#include "malloc.h"
|
|
|
|
// A PageMap maps page numbers to void* pointers.
|
|
// The AMD64 has 64-bit addresses and 4096-byte pages, so
|
|
// the page numbers are 52 bits. We use a four-level radix tree,
|
|
// with 13 bits for each level. This requires 32 kB per level or
|
|
// 128 kB for a table with one entry. Moving to three levels of 18 bits
|
|
// would require 3 MB for a table with one entry, which seems too expensive.
|
|
// This is easy to change.
|
|
// It may be that a balanced tree would be better anyway.
|
|
|
|
// Return the entry for page number pn in m.
|
|
void*
|
|
pmlookup(PageMap *m, uintptr pn)
|
|
{
|
|
int32 i, x;
|
|
void **v;
|
|
|
|
v = &m->level0[0];
|
|
for(i=0; i<PMLevels; i++) {
|
|
// Pick off top PMLevelBits bits as index and shift up.
|
|
x = (pn >> (PMBits - PMLevelBits)) & PMLevelMask;
|
|
pn <<= PMLevelBits;
|
|
|
|
// Walk down using index.
|
|
v = v[x];
|
|
if(v == nil)
|
|
return nil;
|
|
}
|
|
return v;
|
|
}
|
|
|
|
// Set the entry for page number pn in m to s.
|
|
// Return the old value.
|
|
void*
|
|
pminsert(PageMap *m, uintptr pn, void *value)
|
|
{
|
|
int32 i, x;
|
|
void **v, **l;
|
|
|
|
l = nil; // shut up 6c
|
|
v = &m->level0[0];
|
|
for(i=0; i<PMLevels; i++) {
|
|
// Pick off top PMLevelBits bits as index and shift up.
|
|
x = (pn >> (PMBits - PMLevelBits)) & PMLevelMask;
|
|
pn <<= PMLevelBits;
|
|
|
|
// Walk down using index, but remember location of pointer.
|
|
l = &v[x];
|
|
v = *l;
|
|
|
|
// Allocate new level if needed.
|
|
if(v == nil && i < PMLevels-1) {
|
|
v = trivalloc(PMLevelSize * sizeof v[0]);
|
|
*l = v;
|
|
}
|
|
}
|
|
|
|
// Record new value and return old.
|
|
*l = value;
|
|
return v;
|
|
}
|