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Bitcomp Compression#

Bitcomp is a proprietary NVIDIA compressor designed for efficient GPU compression of scientific computing floating-point data. It offers different compression modes, as well as error-bounded lossy compression. It is best suited for smooth or sparse data.

Algorithm Modes#

The low-level API selects the mode through the algorithm field of nvcompBatchedBitcompCompressOpts_t:

Value

Mode

When to Use

0

Default

General numeric data. Usually gives the best compression ratio. This is the default.

1

Sparse

Data that clusters around 0. Usually faster than the default algorithm and compresses sparse data well.

Choosing a mode: start with the default (0) for dense numeric data. Switch to the sparse algorithm (1) when a significant fraction of your values cluster around zero — it is both faster and well-suited to that distribution. Because the right choice depends on your data, benchmark both modes on a representative sample.

Lossy Compression#

Bitcomp can trade exactness for a higher compression ratio on floating-point data (FP16, FP32, FP64). Lossy compression is available through the C, C++ and Python APIs using the mode and delta fields.

How it works#

Lossy compression is based on quantization. As a result:

  • The maximum error between a decompressed value and the original is <= delta/2.

  • delta is rounded down to the nearest power of two (no mantissa), so the error bound is exact.

  • NaN, +Inf, -Inf, and values that would overflow quantization (large inputs with a very small delta) are handled correctly.

You choose how the quantized integers are stored via the compression mode:

  • BITCOMP_LOSSY_FP_TO_SIGNED — quantize to signed integers.

  • BITCOMP_LOSSY_FP_TO_UNSIGNED — quantize to unsigned integers. Only use if you are certain all of your data is positive.

Choosing delta#

delta sets the accuracy/ratio trade-off: a larger delta yields a higher compression ratio but a larger maximum error. Pick the largest delta your application can tolerate, where the acceptable error is delta/2. The scalar delta applies to every chunk in a compression batch. It must remain finite, positive, and normal after conversion to the selected input type; values that are zero, subnormal, infinite, or NaN are rejected. delta is ignored in lossless mode.

Native API#

The Native API provides specialized single-buffer capabilities such as:

  • Partial decompression — decompress only a byte range of a chunk via bitcompPartialUncompress.

  • Host-side (de)compression (the bitcompHost* functions).

  • Massively parallel single-chunk (de)compression (bitcompCompress* and bitcompUncompress functions).

For a worked example of the plan-based single-buffer interface, see examples/bitcomp_native_lossy.cu.

For the complete API, see the Bitcomp sections of the C API, C++ API, and Native API references.