introduce LZ4_DISTANCE_MAX build macro

make it possible to generate LZ4-compressed block
with a controlled maximum offset (necessarily <= 65535).

This could be useful for compatibility with decoders
using a very limited memory budget (<64 KB).

Answer #154

2 files changed, 48 insertions, 14 deletions

diff --git a/doc/lz4_manual.html b/doc/lz4_manual.html
index 1c6dba7..ef1a8b5 100644
--- a/doc/lz4_manual.html
+++ b/doc/lz4_manual.html
@@ -396,6 +396,7 @@ union LZ4_stream_u {
   Note : initialization fails if size and alignment conditions are not respected.
          In which case, the function will @return NULL.
   Note2: An LZ4_stream_t structure guarantees correct alignment and size.
+  Note3: Before v1.9.0, use LZ4_resetStream() instead
  
 </p></pre><BR>
 
diff --git a/doc/lz4frame_manual.html b/doc/lz4frame_manual.html
index 4277c3c..d5496a1 100644
--- a/doc/lz4frame_manual.html
+++ b/doc/lz4frame_manual.html
@@ -237,25 +237,58 @@ LZ4F_errorCode_t LZ4F_freeDecompressionContext(LZ4F_dctx* dctx);
 
 <a name="Chapter10"></a><h2>Streaming decompression functions</h2><pre></pre>
 
+<pre><b>size_t LZ4F_headerSize(const void* src, size_t srcSize);
+</b><p>  Provide the header size of a frame starting at `src`.
+ `srcSize` must be >= LZ4F_MIN_SIZE_TO_KNOW_HEADER_LENGTH,
+  which is enough to decode the header length.
+ @return : size of frame header
+           or an error code, which can be tested using LZ4F_isError()
+  note : Frame header size is variable, but is guaranteed to be
+         >= LZ4F_HEADER_SIZE_MIN bytes, and <= LZ4F_HEADER_SIZE_MAX bytes.
+ 
+</p></pre><BR>
+
 <pre><b>size_t LZ4F_getFrameInfo(LZ4F_dctx* dctx,
                                      LZ4F_frameInfo_t* frameInfoPtr,
                                      const void* srcBuffer, size_t* srcSizePtr);
 </b><p>  This function extracts frame parameters (max blockSize, dictID, etc.).
-  Its usage is optional.
-  Extracted information is typically useful for allocation and dictionary.
-  This function works in 2 situations :
-   - At the beginning of a new frame, in which case
-     it will decode information from `srcBuffer`, starting the decoding process.
-     Input size must be large enough to successfully decode the entire frame header.
-     Frame header size is variable, but is guaranteed to be <= LZ4F_HEADER_SIZE_MAX bytes.
-     It's allowed to provide more input data than this minimum.
-   - After decoding has been started.
-     In which case, no input is read, frame parameters are extracted from dctx.
-   - If decoding has barely started, but not yet extracted information from header,
+  Its usage is optional: user can call LZ4F_decompress() directly.
+
+  Extracted information will fill an existing LZ4F_frameInfo_t structure.
+  This can be useful for allocation and dictionary identification purposes.
+
+  LZ4F_getFrameInfo() can work in the following situations :
+
+  1) At the beginning of a new frame, before any invocation of LZ4F_decompress().
+     It will decode header from `srcBuffer`,
+     consuming the header and starting the decoding process.
+
+     Input size must be large enough to contain the full frame header.
+     Frame header size can be known beforehand by LZ4F_headerSize().
+     Frame header size is variable, but is guaranteed to be >= LZ4F_HEADER_SIZE_MIN bytes,
+     and not more than <= LZ4F_HEADER_SIZE_MAX bytes.
+     Hence, blindly providing LZ4F_HEADER_SIZE_MAX bytes or more will always work.
+     It's allowed to provide more input data than the header size,
+     LZ4F_getFrameInfo() will only consume the header.
+
+     If input size is not large enough,
+     aka if it's smaller than header size,
+     function will fail and return an error code.
+
+  2) After decoding has been started,
+     it's possible to invoke LZ4F_getFrameInfo() anytime
+     to extract already decoded frame parameters stored within dctx.
+
+     Note that, if decoding has barely started,
+     and not yet read enough information to decode the header,
      LZ4F_getFrameInfo() will fail.
-  The number of bytes consumed from srcBuffer will be updated within *srcSizePtr (necessarily <= original value).
-  Decompression must resume from (srcBuffer + *srcSizePtr).
- @return : an hint about how many srcSize bytes LZ4F_decompress() expects for next call,
+
+  The number of bytes consumed from srcBuffer will be updated in *srcSizePtr (necessarily <= original value).
+  LZ4F_getFrameInfo() only consumes bytes when decoding has not yet started,
+  and when decoding the header has been successful.
+  Decompression must then resume from (srcBuffer + *srcSizePtr).
+
+ @return : a hint about how many srcSize bytes LZ4F_decompress() expects for next call,
            or an error code which can be tested using LZ4F_isError().
   note 1 : in case of error, dctx is not modified. Decoding operation can resume from beginning safely.
   note 2 : frame parameters are *copied into* an already allocated LZ4F_frameInfo_t structure.