[Experiment] Split native deflate hash allocation on Win64

src/native/external/zlib-ng-version.txt

@@ -10,3 +10,8 @@ We have removed the following folders from our local copy as these files are not
 - zlib-ng/test/
 - zlib-ng/arch/s390/self-hosted-builder/
 
+Local modifications:
+
+- On _WIN64, deflate.c and deflate.h allocate the hash-head table separately,
+  preserving its 64-byte alignment and keeping window and prev adjacent in the
+  original allocation. Both allocations are released through the saved free callback.

src/native/external/zlib-ng/deflate.c

@@ -196,12 +196,17 @@ static const config configuration_table[10] = {
 #endif
 
 /* ===========================================================================
- * Allocate a big buffer and divide it up into the various buffers deflate needs.
+ * Allocate the various buffers deflate needs.
  * Handles alignment of allocated buffer and alignment of individual buffers.
  */
 Z_INTERNAL deflate_allocs* alloc_deflate(PREFIX3(stream) *strm, int windowBits, int lit_bufsize) {
     int curr_size = 0;
 
+#ifdef _WIN64
+    if (HASH_SIZE > (INT32_MAX - 63) / sizeof(Pos))
+        return NULL;
+#endif
+
     /* Define sizes */
     int window_size = DEFLATE_ADJUST_WINDOW_SIZE((1 << windowBits) * 2);
     int prev_size = (1 << windowBits) * (int)sizeof(Pos);
@@ -219,9 +224,11 @@ Z_INTERNAL deflate_allocs* alloc_deflate(PREFIX3(stream) *strm, int windowBits,
     int prev_pos = PAD_64(curr_size);
     curr_size = prev_pos + prev_size;
 
+#ifndef _WIN64
     LOGSZP("head", head_size, PAD_64(curr_size), PADSZ(curr_size,64));
     int head_pos = PAD_64(curr_size);
     curr_size = head_pos + head_size;
+#endif
 
     LOGSZP("pending", pending_size, PAD_64(curr_size), PADSZ(curr_size,64));
     int pending_pos = PAD_64(curr_size);
@@ -254,7 +261,17 @@ Z_INTERNAL deflate_allocs* alloc_deflate(PREFIX3(stream) *strm, int windowBits,
     /* Assign buffers */
     alloc_bufs->window = (unsigned char *)HINT_ALIGNED_WINDOW(buff + window_pos);
     alloc_bufs->prev = (Pos *)HINT_ALIGNED_64(buff + prev_pos);
+#ifdef _WIN64
+    /* Split out the hash table while keeping window and prev adjacent in the owner allocation. */
+    alloc_bufs->head_buf_start = (char *)strm->zalloc(strm->opaque, 1, head_size + 63);
+    if (alloc_bufs->head_buf_start == NULL) {
+        alloc_bufs->zfree(strm->opaque, alloc_bufs->buf_start);
+        return NULL;
+    }
+    alloc_bufs->head = (Pos *)HINT_ALIGNED_64((char *)PAD_64(alloc_bufs->head_buf_start));
+#else
     alloc_bufs->head = (Pos *)HINT_ALIGNED_64(buff + head_pos);
+#endif
     alloc_bufs->pending_buf = (unsigned char *)HINT_ALIGNED_64(buff + pending_pos);
     alloc_bufs->state = (deflate_state *)HINT_ALIGNED_16(buff + state_pos);
 
@@ -271,6 +288,9 @@ static inline void free_deflate(PREFIX3(stream) *strm) {
 
     if (state->alloc_bufs != NULL) {
         deflate_allocs *alloc_bufs = state->alloc_bufs;
+#ifdef _WIN64
+        alloc_bufs->zfree(strm->opaque, alloc_bufs->head_buf_start);
+#endif
         alloc_bufs->zfree(strm->opaque, alloc_bufs->buf_start);
         strm->state = NULL;
     }

src/native/external/zlib-ng/deflate.h

@@ -134,6 +134,9 @@ Pos      quick_insert_string_roll(deflate_state *const s, uint32_t str);
 /* Struct for memory allocation handling */
 typedef struct deflate_allocs_s {
     char            *buf_start;
+#ifdef _WIN64
+    char            *head_buf_start;
+#endif
     free_func        zfree;
     deflate_state   *state;
     unsigned char   *window;