Apple rewrote its TrueType hinting engine from C to Swift for the Fall 2025 releases. The move targets the interpreter’s security risk and delivers a 13% speed boost over the legacy code.

TrueType, first shipped with System 7, still powers fonts like Helvetica and Garamond. Its interpreter handles bytecode from untrusted PDFs and web pages, making it a prime vector for memory‑related exploits.

The Swift rewrite kept pixel‑identical output by matching the C reference exactly. Developers ran a 99.7% coverage unit suite and a fuzzer‑minimized test set of 4,200 PDFs, covering 27 million glyphs, before releasing the code.

By replacing copy‑heavy C structs with Swift projection types and adopting value‑type patterns, the new engine cuts runtime overhead while preserving safety. Apple now ships a memory‑safe, faster TrueType interpreter that protects users and keeps legacy fonts unchanged.