---
title: "Go, Backwards Compatibility, and GODEBUG"
layout: article
---

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This document is kept in the Go repo, not x/website,
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which are tied to a specific release.
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## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.

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constant-time, 64-bit assembly // implementation of P256. The optimizations performed here are described in // detail in: // S.Gueron and V.Krasnov, "Fast prime field elliptic-curve cryptography with // 256-bit primes" // https://link.springer.com/article/10.1007%2Fs13389-014-0090-x // https://eprint.iacr.org/2013/816.pdf //go:build (amd64 || arm64 || ppc64le || s390x) && !purego package nistec import ( "crypto/internal/fips140deps/byteorder" "errors" "math/bits" "runtime" "unsafe" ) // p256Element...

        renamed from `auto_mixed_precision_mkl` to
        `auto_mixed_precision_onednn_bfloat16`. See example usage
        [here](https://www.intel.com/content/www/us/en/developer/articles/guide/getting-started-with-automixedprecisionmkl.html).
    *   **aarch64 CPUs:** Experimental performance optimizations from
        [Compute Library for the Arm® Architecture (ACL)](https://github.com/ARM-software/ComputeLibrary)