36 lines
756 B
Go
36 lines
756 B
Go
package mapsize
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import (
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"math"
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"unsafe"
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)
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type Mapsize struct {
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ptrSize uint64
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intSize uint64
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dataSize uint64
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len uint64
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}
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func New() *Mapsize {
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return &Mapsize{
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ptrSize: uint64(unsafe.Sizeof(&[]int{0}[0])),
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intSize: uint64(unsafe.Sizeof(int(0))),
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}
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}
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func (m *Mapsize) Add(k, v int) {
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m.len++
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// string: ptr=psize, cap=isize, len=isize
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m.dataSize += uint64(k) + uint64(v) + 4*m.intSize + 2*m.ptrSize
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}
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func (m *Mapsize) Size() uint64 {
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hmapSize := m.intSize + 1 + 1 + 2 + 4 + m.ptrSize*4
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buckets := uint64(1 << uint(math.Ceil(math.Log2(float64(m.len)))))
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// entry overhead = key ptr, value ptr, hash, next
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// bucket overhead = 2 ptr (overflow)
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return hmapSize + m.dataSize + m.len*(4*m.ptrSize) + buckets*(2*m.ptrSize)
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}
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