zstd compression - set source size as hint if it is known e. g. by file compression (slightly better performance and/or compression ratio);

although the feature still calling as "experimental", but zstd uses this in its own client since v.1.4 IIRC and the only known drawback would be significant regress of compression ration if guess considerably underestimates, but it does no matter in case of known file size.

CPP/7zip/Archive/ZstdHandler.cpp

@@ -286,6 +286,7 @@ static HRESULT UpdateArchive(
   CMyComPtr<ICompressProgressInfo> localProgress = localProgressSpec;
   localProgressSpec->Init(updateCallback, true);
   NCompress::NZSTD::CEncoder *encoderSpec = new NCompress::NZSTD::CEncoder;
+  encoderSpec->unpackSize = unpackSize;
   CMyComPtr<ICompressCoder> encoder = encoderSpec;
   RINOK(props.SetCoderProps(encoderSpec, NULL));
   RINOK(encoder->Code(fileInStream, outStream, NULL, NULL, localProgress));

CPP/7zip/Compress/ZstdEncoder.cpp

@@ -30,7 +30,8 @@ CEncoder::CEncoder():
   _LdmHashLog(-1),
   _LdmMinMatch(-1),
   _LdmBucketSizeLog(-1),
-  _LdmHashRateLog(-1)
+  _LdmHashRateLog(-1),
+  unpackSize(0)
 {
   _props.clear();
 }
@@ -251,6 +252,11 @@ STDMETHODIMP CEncoder::Code(ISequentialInStream *inStream,
     err = ZSTD_CCtx_setParameter(_ctx, ZSTD_c_contentSizeFlag, 1);
     if (ZSTD_isError(err)) return E_INVALIDARG;
 
+    if (unpackSize) {
+      err = ZSTD_CCtx_setParameter(_ctx, ZSTD_c_srcSizeHint, (int)(unpackSize <= INT_MAX ? unpackSize : INT_MAX));
+      if (ZSTD_isError(err)) return E_INVALIDARG;
+    }
+
     /* enable ldm for large windowlog values */
     if (_WindowLog > 27 && _Long == 0)
       _Long = 1;

CPP/7zip/Compress/ZstdEncoder.h

@@ -67,6 +67,9 @@ class CEncoder:
   Int32 _LdmHashRateLog;
 
 public:
+
+  UInt64 unpackSize;
+
   MY_QUERYINTERFACE_BEGIN2(ICompressCoder)
   MY_QUERYINTERFACE_ENTRY(ICompressSetCoderMt)
   MY_QUERYINTERFACE_ENTRY(ICompressSetCoderProperties)