libvpx: Pull from upstream

source/libvpx/third_party/libmkv/EbmlBufferWriter.c

-// #include <strmif.h>
-#include "EbmlBufferWriter.h"
-#include "EbmlWriter.h"
-// #include <cassert>
-// #include <limits>
-// #include <malloc.h>  //_alloca
-#include <stdlib.h>
-#include <wchar.h>
-#include <string.h>
-
-void Ebml_Write(EbmlGlobal *glob, const void *buffer_in, unsigned long len) {
-  unsigned char *src = glob->buf;
-  src += glob->offset;
-  memcpy(src, buffer_in, len);
-  glob->offset += len;
-}
-
-static void _Serialize(EbmlGlobal *glob, const unsigned char *p, const unsigned char *q) {
-  while (q != p) {
-    --q;
-    memcpy(&(glob->buf[glob->offset]), q, 1);
-    glob->offset++;
-  }
-}
-
-void Ebml_Serialize(EbmlGlobal *glob, const void *buffer_in, unsigned long len) {
-  // assert(buf);
-
-  const unsigned char *const p = (const unsigned char *)(buffer_in);
-  const unsigned char *const q = p + len;
-
-  _Serialize(glob, p, q);
-}
-
-
-void Ebml_StartSubElement(EbmlGlobal *glob, EbmlLoc *ebmlLoc, unsigned long class_id) {
-  Ebml_WriteID(glob, class_id);
-  ebmlLoc->offset = glob->offset;
-  // todo this is always taking 8 bytes, this may need later optimization
-  unsigned long long unknownLen =  0x01FFFFFFFFFFFFFFLLU;
-  Ebml_Serialize(glob, (void *)&unknownLen, 8); // this is a key that says lenght unknown
-}
-
-void Ebml_EndSubElement(EbmlGlobal *glob, EbmlLoc *ebmlLoc) {
-  unsigned long long size = glob->offset - ebmlLoc->offset - 8;
-  unsigned long long curOffset = glob->offset;
-  glob->offset = ebmlLoc->offset;
-  size |=  0x0100000000000000LLU;
-  Ebml_Serialize(glob, &size, 8);
-  glob->offset = curOffset;
-}
-