Compression Modes¶
The compression mode of ZFP algorithm must be specified by 4 parameters included in zfp_compressed_stream
structure (see structure description). This approach allows implementation to meet various constraints on the precision and size of the output. The description of these parameters is given below:
zfp_compressed_stream.maxbits  The maximum number of compressed bits used to represent a block. This parameter sets the hard upper bound on compressed block size, and governs the rate in fixedrate mode. It may also be used as an upper storage limit to prevent implementation from buffer overruns in combination with the accuracy constraints given by
zfp_compressed_stream.maxprec
andzfp_compressed_stream.minexp
.zfp_compressed_stream.minbits  The minimum number of compressed bits used to represent a block. It is recommended to set this parameter to one bit, unless each block is to be stored using a fixed number of bits to facilitate random access (in this case it must be set to the same value as
zfp_compressed_stream.maxbits
).zfp_compressed_stream.maxprec  The maximum number of bit planes encoded. This parameter governs the number of most significant uncompressed bits encoded per transform coefficient. This parameter specifies the precision in fixedprecision mode, as well as provides a mechanism for controlling the relative error.
zfp_compressed_stream.minexp  The smallest absolute bit plane number encoded. The place value of each transform coefficient bit depends on the common floatingpoint exponent, e, that scales the integer coefficients. If the most significant coefficient bit has place value 2^{e}, then the number of bit planes encoded is (one plus) the difference between e and
zfp_compressed_stream.minexp
.
The oneDTL library interface must allow user to choose 1 of 4 compression modes:

enum oneapi::dtl::data_compression::zfp_mode¶
Compression mode.
Values:

enumerator expert¶
Expert mode. All comression parameters are user defined.

enumerator fixed_accuracy¶
Fixed accuracy mode. With defined by user error.

enumerator fixed_precision¶
Fixed precision mode. With defined by user number of bit planes.

enumerator fixed_rate¶
Fixed rate mode. With defined compresed block size.

enumerator expert¶
For now, only the fixedrate
mode is implemented. fixedprecision
mode has only a public interface but has no implementation.
Fixedrate Compression Mode¶
In fixedrate
mode, each ddimensional compressed block of 4^{d} values must be stored using a fixed number of bits given by parameters zfp_compressed_stream.maxbits
and zfp_compressed_stream.minbits
. oneDTL library provides a structure for specifying this mode:

template<typename DataT, std::uint32_t Dimension>
struct oneapi::dtl::data_compression::zfp_fixed_rate¶ Structure for fix rate compression mode initialization.
 tparam DataT
field data type (supported types: float)
 tparam Dimension
dimension of field (supported value: 3)
Public Functions

zfp_fixed_rate(double rate)¶
Constructs a new object to zfp fix rate compresson mode.
 Parameters
rate – mean number compressed bits per value
Accordingly, the compression parameters will be as follows:
minbits = maxbits = ((1 << (2 * d)) * rate) + 0.5
maxprec = ZFP_MAX_PREC
minexp = ZFP_MIN_EXP
Fixedprecision Compression Mode¶
In fixedprecision
mode, the number of bits used to encode a block may vary, but the number of bit planes (i.e., the precision) encoded for the transform coefficients must be fixed. Fixedprecision mode is recommended when relative rather than absolute errors matter. oneDTL structure for specifying this mode:

struct oneapi::dtl::data_compression::zfp_fixed_precision¶
Structure for fix precision compression mode initialization.
Public Functions

inline zfp_fixed_precision(const unsigned int bits)¶
Constructs a new object to zfp fixed presision compresson mode.
 Parameters
bits – the maximum number of bit planes encoded

inline zfp_fixed_precision(const unsigned int bits)¶
And compression parameters looks like:
minbits = ZFP_MIN_BITS
maxbits = ZFP_MAX_BITS
maxprec = zfp_fixed_precision.maxprec
minexp = ZFP_MIN_EXP
Default Compression Parameter Settings¶
The default recommended compression parameter settings that impose no constraints:
ZFP_MAX_BITS = 16658
ZFP_MIN_BITS = 1
ZFP_MAX_PREC = 64
ZFP_MIN_EXP = 1074