Hello,
I am looking for help reviewing the function below. I need to generate
millions of large files in a specific binary format. I do not care about
portability (only used on Little Endian machines). The file format writes
the data in row order, so need to loop over slices of different types and
write them out. I came up with the solution below (it works), but the code
is obviously ugly and possibly fragile. Can you think of another way of
doing this that is at least as efficient, but safer or less verbose?
Thanks,
func (sf *File) writeData(w io.Writer) error {
if sf.NoObs == 0 {
return nil
}
if len(sf.fields) == 0 {
return fmt.Errorf("No fields")
}
bs := make([]byte, sf.recordSize)
//var ptr uintptr
for i := int32(0); i < sf.NoObs; i++ {
offset := 0
for _, f := range sf.fields {
switch f.FieldType {
case StataByte:
v := f.data.([]int8)[i]
bs[offset] = byte(v)
offset++
case StataInt:
v := f.data.([]int16)[i]
bs[offset] = byte(v)
offset++
bs[offset] = byte(v >> 8)
offset++
case StataLong:
v := f.data.([]int32)[i]
bs[offset] = byte(v)
offset++
bs[offset] = byte(v >> 8)
offset++
bs[offset] = byte(v >> 16)
offset++
bs[offset] = byte(v >> 24)
offset++
case StataFloat:
fptr := uintptr(unsafe.Pointer(&f.data.([]float32)[i]))
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 1)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 2)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 3)))
offset++
case StataDouble:
fptr := uintptr(unsafe.Pointer(&f.data.([]float64)[i]))
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 1)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 2)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 3)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 4)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 5)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 6)))
offset++
bs[offset] = byte(*(*byte)(unsafe.Pointer(fptr + 7)))
offset++
default:
return fmt.Errorf("Field type [%d] not supported in field %s", f.FieldType,
f.Name)
}
}
if _, err := w.Write(bs); err != nil {
return err
}
}
return nil
}
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