Release Notes

1.0.1 (2023-12-15)

This patch release primarily addresses minor bug fixes and is needed to update the zfpy Python wheels.


  • A new build macro, BUILD_TESTING_FULL, specifies that all unit tests be built; BUILD_TESTING produces a smaller subset of tests. Full tests and documentation are now included in releases.


  • #169: libm dependency is not always correctly detected.

  • #171: ptrdiff_t is not always imported in Cython.

  • #176: cfp API is not exposed via CMake configuration file.

  • #177: Full test suite is not included in release.

  • #181: rpath is not set correctly in executables.

  • #204: Array strides are not passed by value in zFORp.

  • #220: Errors reported with scikit-build when building zfpy.

1.0.0 (2022-08-01)

This release is not ABI compatible with prior releases due to numerous changes to function signatures and data structures like zfp_field. However, few of the API changes, other than to the cfp C API for compressed arrays, should impact existing code. Note that numerous header files have been renamed or moved relative to prior versions.


  • zfp::const_array: read-only variable-rate array that supports fixed-precision, fixed-accuracy, and reversible modes.

  • Compressed-array classes for 4D data.

  • const versions of array references, pointers, and iterators.

  • A more complete API for pointers and iterators.

  • cfp support for proxy references and pointers, iterators, and (de)serialization.

  • Support for pointers and iterators into array views.

  • zfp::array::size_bytes() allows querying the size of different components of an array object (e.g., payload, cache, index, metadata, …).

  • Templated C++ wrappers around the low-level C API.

  • A generic codec for storing blocks of uncompressed scalars in zfp’s C++ arrays.

  • Additional functions for querying zfp_field and zfp_stream structs.

  • zfp_config: struct that encapsulates compression mode and parameters.

  • Rounding modes for reducing bias in compression errors.

  • New examples: array, iteratorC, and ppm.


  • Headers from array/, cfp/include/, and include/ have been renamed and reorganized into a common include/ directory.

    • The libzfp API is now confined to zfp.h, zfp.hpp, and zfp.mod for C, C++, and Fortran bindings, respectively. These all appear in the top-level include/ directory upon installation.

    • C++ headers now use a .hpp suffix; C headers use a .h suffix.

    • C++ headers like array/zfparray.h have been renamed zfp/array.hpp.

    • C headers like cfp/include/cfparrays.h have been renamed zfp/array.h.

  • size_t and ptrdiff_t replace uint and int for array sizes and strides in the array classes and C/Fortran APIs.

  • zfp_bool replaces int as Boolean type in the C API.

  • bitstream_offset and bitstream_size replace size_t to ensure support for 64-bit offsets into and lengths of bit streams. Consequently, the bitstream API has changed accordingly.

  • All array and view iterators are now random-access iterators.

  • Array inspectors now return const_reference rather than a scalar type like float to allow obtaining a const_pointer to an element of an immutable array.

  • zfp::array::compressed_data() now returns void* instead of uchar*.

  • The array (de)serialization API has been revised, resulting in new zfp::array::header and zfp::exception classes with new exception messages.

  • The array codec class is now responsible for all details regarding compression.

  • The compressed-array C++ implementation has been completely refactored to make it more modular, extensible, and reusable across array types.

  • Array block shapes are now computed on the fly rather than stored.

  • The cfp C API now wraps array objects in structs.

  • The zfPy Python API now supports the more general memoryview over bytes objects for decompression.

  • The zFORp Fortran module name is now zfp instead of zforp_module.

  • Some command-line options for the diffusion example have changed.

  • CMake 3.9 or later is now required for CMake builds.


  • zfp::array::get_header() has been replaced with a zfp::array::header constructor that accepts an array object.

  • ZFP_VERSION_RELEASE is no longer defined (use ZFP_VERSION_PATCH).


  • #66: make install overwrites googletest.

  • #84: Incorrect order of parameters in CUDA memset().

  • #86: C++ compiler warns when __STDC_VERSION__ is undefined.

  • #87: CXXFLAGS is misspelled in cfp/src/Makefile.

  • #98: zfp_stream_maximum_size() underestimates size in reversible mode.

  • #99: Incorrect private_view reads due to missing writeback.

  • #109: Unused CPython array is incompatible with PyPy.

  • #112: PGI compiler bug causes issues with memory alignment.

  • #119: All-subnormal blocks may cause floating-point overflow.

  • #121: CUDA bit offsets are limited to 32 bits.

  • #122: make install does not install zfp command-line utility.

  • #125: OpenMP bit offsets are limited to 32 bits.

  • #126: make install does not install Fortran module.

  • #127: Reversible mode reports incorrect compressed block size.

  • #150: cmocka tests do not build on macOS.

  • #154: Thread safety is broken in private_view and private_const_view.

  • ZFP_MAX_BITS is off by one.

  • diffusionC, iteratorC are not being built with gmake.

0.5.5 (2019-05-05)


  • Support for reversible (lossless) compression of floating-point and integer data.

  • Methods for serializing and deserializing zfp’s compressed arrays.

  • Python bindings for compressing NumPy arrays.

  • Fortran bindings to zfp’s high-level C API.


  • The default compressed-array cache size is now a function of the total number of array elements, irrespective of array shape.


  • Incorrect handling of execution policy in zfp utility.

  • Incorrect handling of decompression via header in zfp utility.

  • Incorrect cleanup of device memory in CUDA decompress.

  • Missing tests for failing mallocs.

  • CMake does not install CFP when built.

  • zfp_write_header() and zfp_field_metadata() succeed even if array dimensions are too large to fit in header.

0.5.4 (2018-10-01)


  • Support for CUDA fixed-rate compression and decompression.

  • Views into compressed arrays for thread safety, nested array indexing, slicing, and array subsetting.

  • C language bindings for compressed arrays.

  • Support for compressing and decompressing 4D data.


  • Execution policy now applies to both compression and decompression.

  • Compressed array accessors now return Scalar type instead of const Scalar& to avoid stale references to evicted cache lines.


  • Incorrect handling of negative strides.

  • Incorrect handling of arrays with more than 232 elements in zfp command-line tool.

  • bitstream is not C++ compatible.

  • Minimum cache size request is not respected.

0.5.3 (2018-03-28)


  • Support for OpenMP multithreaded compression (but not decompression).

  • Options for OpenMP execution in zfp command-line tool.

  • Compressed-array support for copy construction and assignment via deep copies.

  • Virtual destructors to enable inheritance from zfp arrays.


  • zfp_decompress() now returns the number of compressed bytes processed so far, i.e., the same value returned by zfp_compress().

0.5.2 (2017-09-28)


  • Iterators and proxy objects for pointers and references.

  • Example illustrating how to use iterators and pointers.


  • Diffusion example now optionally uses iterators.

  • Moved internal headers under array to array/zfp.

  • Modified 64-bit integer typedefs to avoid the C89 non-compliant long long and allow for user-supplied types and literal suffixes.

  • Renamed compile-time macros that did not have a ZFP prefix.

  • Rewrote documentation in reStructuredText and added complete documentation of all public functions, classes, types, and macros.


  • Issue with setting stream word type via CMake.

0.5.1 (2017-03-28)

This release primarily fixes a few minor issues but also includes changes in anticipation of a large number of planned future additions to the library. No changes have been made to the compressed format, which is backwards compatible with version 0.5.0.


  • High-level API support for integer types.

  • Example that illustrates in-place compression.

  • Support for CMake builds.

  • Documentation that discusses common issues with using zfp.


  • Separated library version from CODEC version and added version string.

  • Corrected inconsistent naming of BIT_STREAM macros in code and documentation.

  • Renamed some of the header bit mask macros.

  • stream_skip() and stream_flush() now return the number of bits skipped or output.

  • Renamed stream_block() and stream_delta() to make it clear that they refer to strided streams. Added missing definition of stream_stride_block().

  • Changed int and uint types in places to use ptrdiff_t and size_t where appropriate.

  • Changed API for zfp_set_precision() and zfp_set_accuracy() to not require the scalar type.

  • Added missing static keyword in decode_block().

  • Changed testzfp to allow specifying which tests to perform on the command line.

  • Modified directory structure.


  • Bug that prevented defining uninitialized arrays.

  • Incorrect computation of array sizes in zfp_field_size().

  • Minor issues that prevented code from compiling on Windows.

  • Issue with fixed-accuracy headers that caused unnecessary storage.

0.5.0 (2016-02-29)

This version introduces backwards incompatible changes to the CODEC.


  • Modified CODEC to more efficiently encode blocks whose values are all zero or are smaller in magnitude than the absolute error tolerance. This allows representing “empty” blocks using only one bit each.

  • Added functions for compactly encoding the compression parameters and field meta data, e.g., for producing self-contained compressed streams. Also added functions for reading and writing a header containing these parameters.


  • Changed behavior of zfp_compress() and zfp_decompress() to not automatically rewind the bit stream. This makes it easier to concatenate multiple compressed bit streams, e.g., when compressing vector fields or multiple scalars together.

  • Changed the zfp example program interface to allow reading and writing compressed streams, optionally with a header. The zfp tool can now be used to compress and decompress files as a stand alone utility.

0.4.1 (2015-12-28)


  • Added simple.c as a minimal example of how to call the compressor.


  • Changed compilation of diffusion example to output two executables: one with and one without compression.


  • Bug that caused segmentation fault when compressing 3D arrays whose dimensions are not multiples of four. Specifically, arrays of dimensions nx × ny × nz, with ny not a multiple of four, were not handled correctly.

  • Modified examples/fields.h to ensure standard compliance. Previously, C99 support was needed to handle the hex float constants, which are not supported in C++98.

0.4.0 (2015-12-05)

This version contains substantial changes to the compression algorithm that improve PSNR by about 6 dB and speed by a factor of 2-3. These changes are not backward compatible with previous versions of zfp.


  • Support for 31-bit and 63-bit integer data, as well as shorter integer types.

  • New examples for evaluating the throughput of the (de)compressor and for compressing grayscale images in the pgm format.

  • Frequently asked questions.


  • Rewrote compression codec entirely in C to make linking and calling easier from other programming languages, and to expose the low-level interface through C instead of C++. This necessitated significant changes to the API as well.

  • Minor changes to the C++ compressed array API, as well as major implementation changes to support the C library. The namespace and public types are now all in lower case.


  • Support for general fixed-point decorrelating transforms.

0.3.2 (2015-12-03)


  • Bug in Array::get() that caused the wrong cached block to be looked up, thus occasionally copying incorrect values back to parts of the array.

0.3.1 (2015-05-06)


  • Rare bug caused by exponent underflow in blocks with no normal and some subnormal numbers.

0.3.0 (2015-03-03)

This version modifies the default decorrelating transform to one that uses only additions and bit shifts. This new transform, in addition to being faster, also has some theoretical optimality properties and tends to improve rate distortion. This change is not backwards compatible.


  • Compile-time support for parameterized transforms, e.g., to support other popular transforms like DCT, HCT, and Walsh-Hadamard.

  • Floating-point traits to reduce the number of template parameters. It is now possible to declare a 3D array as Array3<float>, for example.

  • Functions for setting the array scalar type and dimensions.

  • testzfp for regression testing.


  • Made forward transform range preserving: (-1, 1) is mapped to (-1, 1). Consequently Q1.62 fixed point can be used throughout.

  • Changed the order in which bits are emitted within each bit plane to be more intelligent. Group tests are now deferred until they are needed, i.e., just before the value bits for the group being tested. This improves the quality of fixed-rate encodings, but has no impact on compressed size.

  • Made several optimizations to improve performance.

  • Consolidated several header files.

0.2.1 (2014-12-12)


  • Win64 support via Microsoft Visual Studio compiler.

  • Documentation of the expected output for the diffusion example.


  • Made several minor changes to suppress compiler warnings.


  • Broken support for IBM’s xlc compiler.

0.2.0 (2014-12-02)

The compression interface from zfpcompress was relocated to a separate library, called libzfp, and modified to be callable from C. This API now uses a parameter object (zfp_params) to specify array type and dimensions as well as compression parameters.


  • Several utility functions were added to simplify libzfp usage:

    • Functions for setting the rate, precision, and accuracy. Corresponding functions were also added to the Codec class.

    • A function for estimating the buffer size needed for compression.

  • The Array class functionality was expanded:

    • Support for accessing the compressed bit stream stored with an array, e.g., for offline compressed storage and for initializing an already compressed array.

    • Functions for dynamically specifying the cache size.

    • The default cache is now direct-mapped instead of two-way associative.


  • Corrected the value of the lowest possible bit plane to account for both the smallest exponent and the number of bits in the significand.

  • Corrected inconsistent use of rate and precision. The rate refers to the number of compressed bits per floating-point value, while the precision refers to the number of uncompressed bits. The Array API was changed accordingly.

0.1.0 (2014-11-12)

Initial beta release.