Single-file decoder script can now (optionally) create an encoder

To complement the single-file decoder a new script was added to create an amalgamated single-file of all of the Zstd source, along with examples and (simple) tests.

lib/compress/fse_compress.c

@@ -626,7 +626,9 @@ size_t FSE_compress_usingCTable (void* dst, size_t dstSize,
 size_t FSE_compressBound(size_t size) { return FSE_COMPRESSBOUND(size); }
 
 #define CHECK_V_F(e, f) size_t const e = f; if (ERR_isError(e)) return e
+#ifndef CHECK_F
 #define CHECK_F(f)   { CHECK_V_F(_var_err__, f); }
+#endif
 
 /* FSE_compress_wksp() :
  * Same as FSE_compress2(), but using an externally allocated scratch buffer (`workSpace`).

lib/compress/huf_compress.c

@@ -41,7 +41,9 @@
 #define HUF_isError ERR_isError
 #define HUF_STATIC_ASSERT(c) DEBUG_STATIC_ASSERT(c)   /* use only *after* variable declarations */
 #define CHECK_V_F(e, f) size_t const e = f; if (ERR_isError(e)) return e
+#ifndef CHECK_F
 #define CHECK_F(f)   { CHECK_V_F(_var_err__, f); }
+#endif
 
 
 /* **************************************************************

lib/compress/zstd_compress.c

@@ -3749,13 +3749,16 @@ static size_t ZSTD_nextInputSizeHint(const ZSTD_CCtx* cctx)
     return hintInSize;
 }
 
-static size_t ZSTD_limitCopy(void* dst, size_t dstCapacity,
-                       const void* src, size_t srcSize)
+#ifndef ZSTD_DECOMPRESS_INTERNAL_H /* zstd_decompress.c has the same function */
+MEM_STATIC size_t ZSTD_limitCopy(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
 {
     size_t const length = MIN(dstCapacity, srcSize);
-    if (length) memcpy(dst, src, length);
+    if (length > 0) {
+        memcpy(dst, src, length);
+    }
     return length;
 }
+#endif
 
 /** ZSTD_compressStream_generic():
  *  internal function for all *compressStream*() variants

lib/decompress/zstd_decompress.c

@@ -1498,6 +1498,7 @@ size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize)
 
 /* *****   Decompression   ***** */
 
+#ifndef ZSTD_COMPRESS_H /* zstd_compress.c has the same function */
 MEM_STATIC size_t ZSTD_limitCopy(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
 {
     size_t const length = MIN(dstCapacity, srcSize);
@@ -1506,7 +1507,7 @@ MEM_STATIC size_t ZSTD_limitCopy(void* dst, size_t dstCapacity, const void* src,
     }
     return length;
 }
-
+#endif
 
 size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input)
 {