# Herbie 1.4 Release Notes

The Herbie developers are excited to announce Herbie 1.4! This release continues a focus on speed and predictability.

Herbie automatically improves the accuracy of floating point expressions. This avoids the bugs, errors, and surprises that so often occur when working with floating point. Since our PLDI'15 paper, we've been hard at work making Herbie more versatile and easier to use.

## Major features of this release

Faster simplification: Herbie now uses the Egg library to simplify expressions. Egg is roughly a hundred times faster than Herbie's existing simplifier; Herbie with Egg is roughly twice as fast overall. Egg is packaged for Windows, macOS, and Linux, so it should be transparently usable on all platforms.

Input search: Herbie now uses interval arithmetic to more efficiently sample valid inputs. The "Cannot sample enough valid points" error message should now be rarer, because Herbie should be much better at finding valid inputs, whereever they are.

## Improvement to core algorithm

• Simplification now uses the Egg library; Herbie's existing e-graph library has been spun out as regraph, which can be used by other Racket projects.
• Herbie's input search pass now analyzes the input program and its precondition and avoids sampling invalid inputs as much as possible.
• The interval arithmetic library has gained support for movability flags, which allow Herbie to detect and skip unsamplable input points.
• The core program evaluator now operates in batch mode, speeding Herbie when it generates thousands of program candidates.
• The interval arithmetic library has been spun out as rival, which other Racket projects can now use. Minor bugs in the interval library have been fixed, and support has been extended to more functions.
• One form of exponential growth in the rewrite algorithm is fixed by a cache, eliminating a common cause of timeouts.
• Herbie's "final simplify" step no longer does constant folding, eliminating a rare source of accuracy regression.

## Usability improvements

• Safari has been tested, and major bugs have been fixed.
• The documentation is now a bit clearer and more approachable.
• Herbie now blames the correct variable when a precondition is unsatisfiable.
• The :spec property and let* construct are now supported.
• Herbie now tries a little hard to produce simpler expressions. This change won't totally fix Herbie's weird output, but should help a bit.
• Herbie now aggregates profile information across a whole report and presents it in an interactive, JavaScript-enabled form on the "Metrics" page. This should help us keep speeding up Herbie.
• Some "internal" measures on the details page now show correct data.

## Code Cleanup

• Several herbie dependencies have been spun out as libraries, including the C and TeX translators (fpbench), the e-graph implementation (regraph), and the interval library (rival). Other projects can now use these components.
• Herbie's support for complex number arithmetic has been extracted to a beta-quality external library. In the future we hope to provide a standard plugin API not only for complex numbers but also vectors, matrices, and other mathematical objects.
• Herbie's support for multi- and mixed-precision operations continues to improve, though there is more to do. We are targeting Herbie 1.5 for this to be "done".
• Many obsolete functions and data structures have been removed. A new random-number algorithm means pre-1.4 seeds will produce different results on Herbie 1.4.
• The code base was reorganized to split the web code across multiple files, with cleaner separation between responsibilities.
• Herbie now uses Github Actions, not Travis, as its continuous integration service. This already means that single-precision and posit support is better tested, and we hope to leverage Github Actions more in the future.

## Try it out!

We're want Herbie to be more useful to scientists, engineers, and programmers around the world. We've got a lot of features we're excited to work on in the coming months. Please report bugs, join the mailing list, or contribute.

If you find Herbie useful, let us know!