Eagerly initialize the ringbuffer tail. PiperOrigin-RevId: 982189567

diff --git a/c/enc/backward_references_hq.c b/c/enc/backward_references_hq.c
index 07e82d1..a4718b5 100644
--- a/c/enc/backward_references_hq.c
+++ b/c/enc/backward_references_hq.c

@@ -433,8 +433,6 @@
   const CompoundDictionary* addon = &params->dictionary.compound;
   size_t gap = addon->total_size;
 
-  BROTLI_DCHECK(cur_ix_masked + max_len <= ringbuffer_mask + 1);
-
   EvaluateNode(block_start + stream_offset, pos, max_backward_limit, gap,
       starting_dist_cache, model, queue, nodes);
 

diff --git a/c/enc/hash.h b/c/enc/hash.h
index c88a6c5..2e0b047 100644
--- a/c/enc/hash.h
+++ b/c/enc/hash.h

@@ -568,8 +568,6 @@
     source = (const uint8_t*)BROTLI_UNALIGNED_LOAD_PTR((const uint8_t**)tail);
   }
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   for (i = 0; i < 4; ++i) {
     const size_t distance = (size_t)distance_cache[i];
     size_t offset;
@@ -679,8 +677,6 @@
     source = (const uint8_t*)BROTLI_UNALIGNED_LOAD_PTR((const uint8_t**)tail);
   }
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   while (item == 0) {
     size_t offset;
     size_t distance;

diff --git a/c/enc/hash_forgetful_chain_inc.h b/c/enc/hash_forgetful_chain_inc.h
index b653698..31269bc 100644
--- a/c/enc/hash_forgetful_chain_inc.h
+++ b/c/enc/hash_forgetful_chain_inc.h

@@ -213,8 +213,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < NUM_LAST_DISTANCES_TO_CHECK; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/hash_longest_match64_inc.h b/c/enc/hash_longest_match64_inc.h
index 3131451..4e6d7d6 100644
--- a/c/enc/hash_longest_match64_inc.h
+++ b/c/enc/hash_longest_match64_inc.h

@@ -178,8 +178,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/hash_longest_match64_simd_inc.h b/c/enc/hash_longest_match64_simd_inc.h
index 17dc67d..ea16330 100644
--- a/c/enc/hash_longest_match64_simd_inc.h
+++ b/c/enc/hash_longest_match64_simd_inc.h

@@ -195,8 +195,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/hash_longest_match_inc.h b/c/enc/hash_longest_match_inc.h
index 674dced..ddf155f 100644
--- a/c/enc/hash_longest_match_inc.h
+++ b/c/enc/hash_longest_match_inc.h

@@ -178,8 +178,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/hash_longest_match_quickly_inc.h b/c/enc/hash_longest_match_quickly_inc.h
index 12fdb44..8fa8bf9 100644
--- a/c/enc/hash_longest_match_quickly_inc.h
+++ b/c/enc/hash_longest_match_quickly_inc.h

@@ -165,8 +165,6 @@
   size_t cached_backward = (size_t)distance_cache[0];
   size_t prev_ix = cur_ix - cached_backward;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   out->len_code_delta = 0;
   if (prev_ix < cur_ix && cached_backward <= max_backward) {
     prev_ix &= (uint32_t)ring_buffer_mask;

diff --git a/c/enc/hash_longest_match_simd_inc.h b/c/enc/hash_longest_match_simd_inc.h
index 075f6da..6b92380 100644
--- a/c/enc/hash_longest_match_simd_inc.h
+++ b/c/enc/hash_longest_match_simd_inc.h

@@ -170,8 +170,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/hash_longest_match_simd_opt_inc.h b/c/enc/hash_longest_match_simd_opt_inc.h
index 075f6da..6b92380 100644
--- a/c/enc/hash_longest_match_simd_opt_inc.h
+++ b/c/enc/hash_longest_match_simd_opt_inc.h

@@ -170,8 +170,6 @@
   out->len = 0;
   out->len_code_delta = 0;
 
-  BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask + 1);
-
   /* Try last distance first. */
   for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) {
     const size_t backward = (size_t)distance_cache[i];

diff --git a/c/enc/ringbuffer.h b/c/enc/ringbuffer.h
index 5bb75ed..71ba9a5 100644
--- a/c/enc/ringbuffer.h
+++ b/c/enc/ringbuffer.h

@@ -123,9 +123,11 @@
        later when we copy the last two bytes to the first two positions. */
     rb->buffer_[rb->size_ - 2] = 0;
     rb->buffer_[rb->size_ - 1] = 0;
-    /* Initialize tail; might be touched by "best_len++" optimization when
-       ring buffer is "full". */
-    rb->buffer_[rb->size_] = 241;
+    /* Mirror the bytes written by the "first write" shortcut (see above) into
+       the tail.  That deliberately avoids initializing the ring buffer tail,
+       but that requires that we copy the bytes here. */
+    memcpy(&rb->buffer_[rb->size_], rb->buffer_,
+           BROTLI_MIN(size_t, rb->pos_, rb->tail_size_));
   }
   {
     const size_t masked_pos = rb->pos_ & rb->mask_;