build macro ZSTD_DECODER_INTERNAL_BUFFER

just to make the topic more accessible for potential users.

lib/README.md

@@ -155,11 +155,11 @@ The file structure is designed to make this selection manually achievable for an
 - The build macro `ZSTD_NO_INTRINSICS` can be defined to disable all explicit intrinsics.
   Compiler builtins are still used.
 
-- The build macro `ZSTD_LITBUFFEREXTRASIZE` can be set to control the amount of extra memory used
+- The build macro `ZSTD_DECODER_INTERNAL_BUFFER` can be set to control
-  during decompression to store literals.  This defaults to 64kB.  Reducing it can reduce the
+  the amount of extra memory used during decompression to store literals.
-  memory footprint required for decompression by increasing the portion of the literal buffer that
+  This defaults to 64kB.  Reducing this value reduces the memory footprint of
-  is stored in the unwritten portion of the dst buffer, at the cost of performance impact for
+  `ZSTD_DCtx` decompression contexts,
-  decompression.
+  but might also result in a small decompression speed cost.
 
 
 #### Windows : using MinGW+MSYS to create DLL

lib/decompress/zstd_decompress_internal.h

@@ -106,10 +106,15 @@ typedef struct {
     size_t ddictPtrCount;
 } ZSTD_DDictHashSet;
 
-#ifndef ZSTD_LITBUFFEREXTRASIZE
+#ifndef ZSTD_DECODER_INTERNAL_BUFFER
-#define ZSTD_LITBUFFEREXTRASIZE    (1 << 16) /* extra buffer reduces amount of dst required to store litBuffer */
+#  define ZSTD_DECODER_INTERNAL_BUFFER  (1 << 16)
 #endif
 
+#define ZSTD_LBMAX (128 << 10)
+
+/* extra buffer, compensates amount of dst required to store litBuffer */
+#define ZSTD_LITBUFFEREXTRASIZE  MIN(ZSTD_DECODER_INTERNAL_BUFFER, ZSTD_LBMAX)
+
 typedef enum {
     ZSTD_not_in_dst = 0,  /* Stored entirely within litExtraBuffer */
     ZSTD_in_dst = 1,           /* Stored entirely within dst (in memory after current output write) */