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package memsize
import (
"math/bits"
)
const (
uintptrBits = 32 << (uint64(^uintptr(0)) >> 63)
uintptrBytes = uintptrBits / 8
bmBlockRange = 1 * 1024 * 1024 // bytes covered by bmBlock
bmBlockWords = bmBlockRange / uintptrBits
)
// bitmap is a sparse bitmap.
type bitmap struct {
blocks map[uintptr]*bmBlock
}
func newBitmap() *bitmap {
return &bitmap{make(map[uintptr]*bmBlock)}
}
// markRange sets n consecutive bits starting at addr.
func (b *bitmap) markRange(addr, n uintptr) {
for end := addr + n; addr < end; {
block, baddr := b.block(addr)
for i := baddr; i < bmBlockRange && addr < end; i++ {
block.mark(i)
addr++
}
}
}
// isMarked returns the value of the bit at the given address.
func (b *bitmap) isMarked(addr uintptr) bool {
block, baddr := b.block(addr)
return block.isMarked(baddr)
}
// countRange returns the number of set bits in the range (addr,addr+n).
func (b *bitmap) countRange(addr, n uintptr) uintptr {
c := uintptr(0)
for end := addr + n; addr < end; {
block, baddr := b.block(addr)
bend := uintptr(bmBlockRange - 1)
if baddr+(end-addr) < bmBlockRange {
bend = baddr + (end - addr)
}
c += uintptr(block.count(baddr, bend))
// Move addr to next block.
addr += bmBlockRange - baddr
}
return c
}
// block finds the block corresponding to the given memory address.
// It also returns the block's starting address.
func (b *bitmap) block(addr uintptr) (*bmBlock, uintptr) {
index := addr / bmBlockRange
block := b.blocks[index]
if block == nil {
block = new(bmBlock)
b.blocks[index] = block
}
return block, addr % bmBlockRange
}
// size returns the sum of the byte sizes of all blocks.
func (b *bitmap) size() uintptr {
return uintptr(len(b.blocks)) * bmBlockWords * uintptrBytes
}
// utilization returns the mean percentage of one bits across all blocks.
func (b *bitmap) utilization() float32 {
var avg float32
for _, block := range b.blocks {
avg += float32(block.count(0, bmBlockRange-1)) / float32(bmBlockRange)
}
return avg / float32(len(b.blocks))
}
// bmBlock is a bitmap block.
type bmBlock [bmBlockWords]uintptr
// mark sets the i'th bit to one.
func (b *bmBlock) mark(i uintptr) {
b[i/uintptrBits] |= 1 << (i % uintptrBits)
}
// isMarked returns the value of the i'th bit.
func (b *bmBlock) isMarked(i uintptr) bool {
return (b[i/uintptrBits] & (1 << (i % uintptrBits))) != 0
}
// count returns the number of set bits in the range (start,end).
func (b *bmBlock) count(start, end uintptr) (count int) {
br := b[start/uintptrBits : end/uintptrBits+1]
for i, w := range br {
if i == 0 {
w &= blockmask(start)
}
if i == len(br)-1 {
w &^= blockmask(end)
}
count += onesCountPtr(w)
}
return count
}
func blockmask(x uintptr) uintptr {
return ^uintptr(0) << (x % uintptrBits)
}
func onesCountPtr(x uintptr) int {
if uintptrBits == 64 {
return bits.OnesCount64(uint64(x))
}
return bits.OnesCount32(uint32(x))
}