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H5P_SET_NBIT

Sets up the use of the N-Bit filter

Procedure:

H5P_SET_NBIT ( plist_id )

Signature:

herr_t H5Pset_nbit(
          hid_t plist_id
          )

  

Fortran90 Interface: h5pset_nbit_f

Signature:
  SUBROUTINE h5pset_nbit_f(plist_id, hdferr)
    INTEGER(HID_T), INTENT(IN)  :: plist_id
    INTEGER       , INTENT(OUT) :: hdferr

Inputs:
  plist_id - Dataset creation property list identifier.

Outputs:
  hdferr   - Returns 0 if successful and -1 if fails

Parameters:

hid_t plist_id   IN: Dataset creation property list identifier.

Description:

H5P_SET_NBIT sets the N-Bit filter, H5Z_FILTER_NBIT, in the dataset creation property list plist_id.

The HDF5 user can create an N-Bit datatype with the following code:

hid_t nbit_datatype = H5Tcopy(H5T_STD_I32LE);

H5Tset_precision(nbit_datatype, 16);

H5Tset_offset(nbit_datatype, 4);

In memory, one value of the N-Bit datatype in the above example will be stored on a little-endian machine as follows:

byte 3byte 2byte 1byte 0
????????????SPPPPPPPPPPPPPPP????

Note: S - sign bit, P - significant bit, ? - padding bit; For signed integer, the sign bit is included in the precision.

When data of the above datatype is stored on disk using the N-bit filter, all padding bits are chopped off and only significant bits are stored. The values on disk will be something like:

1st value2nd value 
SPPPPPPPPPPPPPPPSPPPPPPPPPPPPPPP...

The N-Bit filter is used effectively for compressing data of an N-Bit datatype as well as a compound and an array datatype with N-Bit fields. However, the datatype classes of the N-Bit datatype or the N-Bit field of the compound datatype or the array datatype are limited to integer or floating-point.

The N-Bit filter supports complex situations where a compound datatype contains member(s) of a compound datatype or an array datatype that has a compound datatype as the base type. However, it does not support the situation where an array datatype has a variable-length or variable-length string as its base datatype. The filter does support the situation where a variable-length or variable-length string is a member of a compound datatype.

The N-Bit filter allows all other HDF5 datatypes (such as time, string, bitfield, opaque, reference, enum, and variable length) to pass through as a no-op.

Like other I/O filters supported by the HDF5 library, application using the N-Bit filter must store data with chunked storage.

By nature, the N-Bit filter should not be used together with other I/O filters.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Example:

Coming Soon!

History:
Release    Change
1.8.0C function introduced in this release.
1.8.8Fortran subroutine introduced in this release.

--- Last Modified: December 20, 2017 | 12:00 PM