5.x series change log

This page summarizes the major functional and performance changes in each release of the 5.x series.

All performance data on this page is measured on an Intel Core i5-9600K clocked at 4.2 GHz, running astcenc using AVX2 and 6 threads.

5.3.0

Status: March 2025

The 5.3.0 release is a minor maintenance release.

General:
- Feature: Reference C builds (ASTCENC_ISA_NONE) now support compiling for big-endian CPUs. Compile with -DASTCENC_BIG_ENDIAN=ON when compiling for a big-endian target; it is not auto-detected.
- Improvement: Builds using GCC now specify -flto=auto to allow parallel link steps, and remove the log warnings about not setting a CPU count parameter value.
- Bug fix: Builds using MSVC cl.exe that do not specify an explicit ISA using the preprocessor configuration defines will now correctly default to the SSE2 backend on x86-64 and the NEON backend on Arm64. Previously they would have defaulted to the reference C implementation, which is around 3.25 times slower.

5.2.0

Status: February 2025

The 5.2.0 release is a minor maintenance release.

This release includes changes to the public interface in the astcenc.h header. We always recommend rebuilding your client-side code using the header from the same release to avoid compatibility issues.

General:
- Change: Changed sRGB alpha channel endpoint expansion to match the revised Khronos Data Format Specification (v1.4.0), which reverts an unintended specification change. Compared to previous releases, this change can cause LSB bit differences in the alpha channel of compressed images.
- Feature: Arm64 builds for Linux added to the GitHub Actions builds, and Arm64 binaries for NEON, 128-bit SVE 128 and 256-bit SVE added to release builds.
- Feature: Added a new codec API, astcenc_compress_cancel(), which can be used to cancel an in-flight compression. This is designed to help make it easier to integrate the codec into an interactive user interface that can respond to user events with low latency.
- Bug fix: Removed incorrect static variable qualifier, which could result in an incorrect tune_mse_overshoot heuristic threshold being used if a user ran multiple concurrent compressions with different settings.

5.1.0

Status: November 2024

The 5.1.0 release is an optimization release, giving moderate performance improvements on all platforms. There are no image quality differences.

General:
- Feature: Added a new CMake build option to control use of native gathers, as they can be slower than scalar loads on some common x86 microarchitectures. Build with -DASTCENC_X86_GATHERS=OFF to disable use of native gathers in AVX2 builds.
- Optimization: Added new gather() abstraction for gathers using byte indices, allowing implementations without gather hardware to skip the byte-to-int index conversion.
- Optimization: Optimized compute_lowest_and_highest_weight() to pre-compute min/max outside of the main loop.
- Optimization: Added improved intrinsics sequence for SSE and AVX2 integer hmin() and hmax().
- Optimization: Added improved intrinsics sequence for vint4(uint8_t*) on systems implementing Arm SVE.

5.0.0

Status: November 2024

The 5.0.0 release is the first stable release in the 5.x series. The main new feature is support for the Arm Scalable Vector Extensions (SVE) SIMD instruction set.

General:
- Bug fix: Fixed incorrect return type in "None" vector library reference implementation.
- Bug fix: Fixed sincos table index under/overflow.
- Feature: Changed ASTCENC_ISA_NATIVE builds to use -march=native and -mcpu=native.
- Feature: Added backend for Arm SVE fixed-width 256-bit builds. These can only run on hardware implementing 256-bit SVE.
- Feature: Added backend for Arm SVE 128-bit builds. These are portable builds and can run on hardware implementing any SVE vector length, but the explicit SVE use is augmented NEON and will only use the bottom 128-bits of each SVE vector.
- Feature: Optimized NEON mask any() and all() functions.
- Feature: Migrated build and test to GitHub Actions pipelines.

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