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byteslicereader.go
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/
byteslicereader.go
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package shapefile
import (
"encoding/binary"
"errors"
"fmt"
"math"
"github.com/twpayne/go-geom"
)
var errUnexpectedEndOfData = errors.New("unexpected end of data")
type byteSliceReader struct {
rest []byte
err error
}
func newByteSliceReader(data []byte) *byteSliceReader {
return &byteSliceReader{
rest: data,
}
}
func (r *byteSliceReader) Err() error {
return r.err
}
func (r *byteSliceReader) readEnds(layout geom.Layout, numParts, numPoints int) []int {
if r.err != nil {
return nil
}
if len(r.rest) < 4*numParts {
r.err = errUnexpectedEndOfData
}
if part := binary.LittleEndian.Uint32(r.rest[:4]); part != 0 {
r.err = fmt.Errorf("%d: invalid part", part)
return nil
}
stride := layout.Stride()
maxPart := stride * numPoints
ends := make([]int, 0, numParts)
for i := 1; i < numParts; i++ {
part := stride * int(binary.LittleEndian.Uint32(r.rest[4*i:4*i+4]))
if part > maxPart {
r.err = fmt.Errorf("%d: invalid part", part)
return nil
}
ends = append(ends, part)
}
ends = append(ends, maxPart)
r.rest = r.rest[4*numParts:]
return ends
}
func (r *byteSliceReader) readFloat64Pair() (float64, float64) {
if r.err != nil {
return 0, 0
}
if len(r.rest) < 16 {
r.err = errUnexpectedEndOfData
return 0, 0
}
a := math.Float64frombits(binary.LittleEndian.Uint64(r.rest[:8]))
b := math.Float64frombits(binary.LittleEndian.Uint64(r.rest[8:16]))
r.rest = r.rest[16:]
return a, b
}
func (r *byteSliceReader) readFloat64s(n int) []float64 {
if r.err != nil {
return nil
}
if len(r.rest) < 8*n {
r.err = errUnexpectedEndOfData
return nil
}
float64s := make([]float64, 0, n)
for i := 0; i < n; i++ {
float64s = append(float64s, math.Float64frombits(binary.LittleEndian.Uint64(r.rest[8*i:8*i+8])))
}
r.rest = r.rest[8*n:]
return float64s
}
func (r *byteSliceReader) readOrdinates(flatCoords []float64, n int, layout geom.Layout, index int) {
if r.err != nil {
return
}
if len(r.rest) < 8*n {
r.err = errUnexpectedEndOfData
return
}
stride := layout.Stride()
for i := 0; i < n; i++ {
flatCoords[i*stride+index] = math.Float64frombits(binary.LittleEndian.Uint64(r.rest[8*i : 8*i+8]))
}
r.rest = r.rest[8*n:]
}
func (r *byteSliceReader) readUint32() int {
if r.err != nil {
return 0
}
if len(r.rest) < 4 {
r.err = errUnexpectedEndOfData
return 0
}
u := int(binary.LittleEndian.Uint32(r.rest[:4]))
r.rest = r.rest[4:]
return u
}
func (r *byteSliceReader) readXYs(flatCoords []float64, n int, layout geom.Layout) {
if r.err != nil {
return
}
if len(r.rest) < 16*n {
r.err = errUnexpectedEndOfData
return
}
stride := layout.Stride()
for i := 0; i < n; i++ {
flatCoords[i*stride] = math.Float64frombits(binary.LittleEndian.Uint64(r.rest[16*i : 16*i+8]))
flatCoords[i*stride+1] = math.Float64frombits(binary.LittleEndian.Uint64(r.rest[16*i+8 : 16*i+16]))
}
r.rest = r.rest[16*n:]
}