55 lines
1,011 B
Go
55 lines
1,011 B
Go
package grib
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import (
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"encoding/binary"
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"math"
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"os"
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mmap "github.com/edsrzf/mmap-go"
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)
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type cube struct {
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mm mmap.MMap // read‑only, U followed by V (float32 LE)
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t, p, lat, lon int
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bytesPerVar int64
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file *os.File
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}
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func openCube(path string) (*cube, error) {
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f, err := os.Open(path)
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if err != nil {
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return nil, err
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}
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mm, err := mmap.Map(f, mmap.RDONLY, 0)
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if err != nil {
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f.Close()
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return nil, err
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}
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const (
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nT = 17
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nP = 34
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nLat = 361
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nLon = 720
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)
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return &cube{mm: mm, t: nT, p: nP, lat: nLat, lon: nLon, bytesPerVar: int64(nT * nP * nLat * nLon * 4), file: f}, nil
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}
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func (c *cube) val(varIdx, ti, pi, y, x int) float32 {
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idx := (((ti*c.p+pi)*c.lat + y) * c.lon) + x
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off := int64(varIdx)*c.bytesPerVar + int64(idx)*4
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bits := binary.LittleEndian.Uint32(c.mm[off : off+4])
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return math.Float32frombits(bits)
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}
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func (c *cube) Close() error {
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if c.mm != nil {
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c.mm.Unmap()
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}
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if c.file != nil {
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return c.file.Close()
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}
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return nil
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}
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