} catch (final UnsupportedEncodingException uee) {}
        dstIndex += scope.length();

        dst[dstIndex++] = (byte) 0x00;

        // now go over scope backwards converting '.' to label length

        int i = dstIndex - 2;
        final int e = i - scope.length();
        int c = 0;

        do {
            if (dst[i] == '.') {
                dst[i] = (byte) c;

        dstIndex += this.scope.length();

        dst[dstIndex++] = (byte) 0x00;

        // now go over scope backwards converting '.' to label length

        int i = dstIndex - 2;
        final int e = i - this.scope.length();
        int c = 0;

        do {
            if (dst[i] == '.') {

 *  New: `OkHttpClient.Builder` now has APIs that use `kotlin.time.Duration`.

 *  New: `mockwebserver3.SocketPolicy` is now a sealed interface. This is one of several
    backwards-incompatible API changes that may impact early adopters of this alpha API.

 *  New: `mockwebserver3.Stream` for duplex streams.

 *  New: `mockwebserver3.MockResponseBody` for streamed response bodies.

                : new NonTerminalImmutableMapEntry<K, V>(key, value, keyBucketHead);
        table[tableIndex] = effectiveEntry;
      } else {
        // We already saw this key, and the first value we saw (going backwards) is the one we are
        // keeping. So we won't touch table[], but we do still want to add the existing entry that
        // we found to entries[] so that we will see this key in the right place when iterating.

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

<!--
This document is kept in the Go repo, not x/website,
because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

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

    // * The element with (index == from) should be kept.
    // * Everything with (index > from) has not been checked yet.

    // Check from the end of the list backwards (minimize expected cost of
    // moving elements when remove() is called). Stop before 'from' because
    // we already know that should be kept.
    for (int n = list.size() - 1; n > from; n--) {

        // First byte should be length of "test" (4) after processing
        assertEquals(4, dst[0]);

        // After processing, dots should be replaced with length markers
        // The scope processing happens backwards
        assertEquals(name.scope.length() + 2, length);
    }

    @Test
    void readScopeWireFormat_withMultipleLabels_shouldParseCorrectly() {
        byte[] src = new byte[100];

      // Both a and b are odd. Assume a > b; then gcd(a - b, b) = gcd(a, b).
      // But in gcd(a - b, b), a - b is even and b is odd, so we can divide out powers of two.

      // We bend over backwards to avoid branching, adapting a technique from
      // http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax

      long delta = a - b; // can't overflow, since a and b are nonnegative

		last := n - 1
		i := last
		fails := 0
		for i < len(s) {
			if s[i] != b[last] {
				o := IndexByte(s[i+1:], b[last])
				if o < 0 {
					return -1
				}
				i += o + 1
			}
			// Step backwards comparing bytes.
			for j := 1; j < n; j++ {
				if s[i-j] != b[last-j] {
					goto next
				}
			}
			return i - last
		next:
			fails++
			i++

        `tf.errors.UnimplementedError` (with an understandable message) to be
        thrown.
        *   `tf.nn.sparse_softmax_cross_entropy_with_logits` forwards and/or
            backwards. See PR
            [47925](https://github.com/tensorflow/tensorflow/pull/47925).
        *   `tf.image.crop_and_resize` gradient w.r.t. either `image` or
            `boxes`. See PR