ml
58 lines
1.5 KiB
Go
58 lines
1.5 KiB
Go
package serial
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import (
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"io"
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"github.com/inkyblackness/hacked/ss1"
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)
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// PositioningEncoder is an Encoder with positioning capabilities.
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type PositioningEncoder struct {
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Encoder
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seeker io.Seeker
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}
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// NewPositioningEncoder returns an Encoder that also implements the Positioner interface.
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// The new Encoder starts with its zero position at the current position in the writer.
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func NewPositioningEncoder(target io.WriteSeeker) *PositioningEncoder {
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return &PositioningEncoder{Encoder: Encoder{target: target}, seeker: target}
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}
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// SetCurPos changes the encoding position to the specified absolute offset.
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func (coder *PositioningEncoder) SetCurPos(offset uint32) {
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if coder.firstError != nil {
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return
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}
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_, coder.firstError = coder.seeker.Seek(int64(offset)-int64(coder.offset), io.SeekCurrent)
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if coder.firstError != nil {
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return
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}
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coder.offset = offset
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}
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const (
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errInvalidWhence ss1.StringError = "seek: invalid whence"
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errSeekBeforeStart ss1.StringError = "seek: seeking before start"
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)
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// Seek repositions the current encoding offset.
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// This implementation does not support a whence value of io.SeekEnd.
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func (coder *PositioningEncoder) Seek(offset int64, whence int) (int64, error) {
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var newPosition int64
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switch whence {
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default:
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return int64(coder.offset), errInvalidWhence
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case io.SeekStart:
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newPosition = offset
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case io.SeekCurrent:
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newPosition = int64(coder.offset) + offset
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}
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if newPosition < 0 {
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return int64(coder.offset), errSeekBeforeStart
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}
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coder.SetCurPos(uint32(newPosition))
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return int64(coder.offset), coder.firstError
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}
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