Caleb Gardner
86 lines
2.2 KiB
Go
86 lines
2.2 KiB
Go
package squashfslow
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import (
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"encoding/binary"
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"errors"
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"io"
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"sync"
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"github.com/CalebQ42/squashfs/internal/metadata"
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"github.com/CalebQ42/squashfs/internal/toreader"
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)
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var errOutOfBounds = errors.New("out of bounds")
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var errUnexpectedOutOfBounds = errors.New("unexpected out of bounds")
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var errNilCollection = errors.New("nil collection")
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type CreateFunction[T any] = func(io.Reader) (T, error)
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type Table[T any] struct {
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totalItems uint32
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itemsPerBlock uint32
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offset uint64
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mut sync.RWMutex
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currentItems []T
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rdr *Reader
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createFunc CreateFunction[T]
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}
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func NewTable[T any](rdr *Reader, start uint64, totalItems uint32, createFunc CreateFunction[T]) *Table[T] {
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var zero T
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return &Table[T]{
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totalItems: totalItems,
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itemsPerBlock: 8192 / uint32(binary.Size(zero)),
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offset: start,
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mut: sync.RWMutex{},
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rdr: rdr,
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createFunc: createFunc,
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}
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}
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func (t *Table[T]) Get(requestedItemIndex uint32) (T, error) {
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t.mut.RLock()
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if requestedItemIndex >= t.totalItems {
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t.mut.RUnlock()
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var zero T
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return zero, errOutOfBounds
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}
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if uint32(len(t.currentItems)) > requestedItemIndex {
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t.mut.RUnlock()
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return t.currentItems[requestedItemIndex], nil
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}
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t.mut.RUnlock()
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return t.fillAndGet(requestedItemIndex)
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}
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func (t *Table[T]) fillAndGet(requestedItemIndex uint32) (T, error) {
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t.mut.Lock()
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defer t.mut.Unlock()
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var offset uint64
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var toRead uint32
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var rdr *toreader.Reader
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var metaRdr metadata.Reader
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var err error
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for uint32(len(t.currentItems)) <= requestedItemIndex {
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rdr = toreader.NewReader(t.rdr.r, int64(t.offset))
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err = binary.Read(rdr, binary.LittleEndian, &offset)
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if err != nil {
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var zero T
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return zero, err
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}
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t.offset += 8
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toRead = min(t.itemsPerBlock, t.totalItems-uint32(len(t.currentItems)))
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oldLen := uint32(len(t.currentItems))
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t.currentItems = append(t.currentItems, make([]T, toRead)...)
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metaRdr = metadata.NewReader(toreader.NewReader(t.rdr.r, int64(offset)), t.rdr.d)
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for i := range toRead {
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t.currentItems[oldLen+i], err = t.createFunc(&metaRdr)
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if err != nil {
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var zero T
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return zero, err
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}
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}
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}
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return t.currentItems[requestedItemIndex], nil
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}
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