From: Yann Collet <cyan@fb.com>
Date: Mon, 25 Oct 2021 15:09:04 +0000 (-0700)
Subject: build macro ZSTD_DECODER_INTERNAL_BUFFER
X-Git-Tag: v1.5.1~1^2~70^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=02be2a830f20e5801386be87d7f816776a068516;p=thirdparty%2Fzstd.git

build macro ZSTD_DECODER_INTERNAL_BUFFER

just to make the topic more accessible for potential users.
---

diff --git a/lib/README.md b/lib/README.md
index 9cbeb8d4f..aab0869af 100644
--- a/lib/README.md
+++ b/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
-  during decompression to store literals.  This defaults to 64kB.  Reducing it can reduce the
-  memory footprint required for decompression by increasing the portion of the literal buffer that
-  is stored in the unwritten portion of the dst buffer, at the cost of performance impact for
-  decompression.
+- The build macro `ZSTD_DECODER_INTERNAL_BUFFER` can be set to control
+  the amount of extra memory used during decompression to store literals.
+  This defaults to 64kB.  Reducing this value reduces the memory footprint of
+  `ZSTD_DCtx` decompression contexts,
+  but might also result in a small decompression speed cost.
 
 
 #### Windows : using MinGW+MSYS to create DLL
diff --git a/lib/decompress/zstd_decompress_internal.h b/lib/decompress/zstd_decompress_internal.h
index ac5586cc7..7f555911d 100644
--- a/lib/decompress/zstd_decompress_internal.h
+++ b/lib/decompress/zstd_decompress_internal.h
@@ -106,10 +106,15 @@ typedef struct {
     size_t ddictPtrCount;
 } ZSTD_DDictHashSet;
 
-#ifndef ZSTD_LITBUFFEREXTRASIZE
-#define ZSTD_LITBUFFEREXTRASIZE    (1 << 16) /* extra buffer reduces amount of dst required to store litBuffer */
+#ifndef ZSTD_DECODER_INTERNAL_BUFFER
+#  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) */