Add CCtx Param Controlling Dict Attachment Behavior

2018-06-21 17:29:25 -04:00
parent e30f13bde0
commit 01bb1c1016
4 changed files with 47 additions and 1 deletions
@@ -1059,6 +1059,28 @@ typedef enum {

    ZSTD_p_forceMaxWindow=1100, /* Force back-reference distances to remain < windowSize,
                              * even when referencing into Dictionary content (default:0) */
+    ZSTD_p_forceAttachDict,  /* ZSTD supports usage of a CDict in-place
+                              * (avoiding having to copy the compression tables
+                              * from the CDict into the working context). Using
+                              * a CDict in this way saves an initial setup step,
+                              * but comes at the cost of more work per byte of
+                              * input. ZSTD has a simple internal heuristic that
+                              * guesses which strategy will be faster. You can
+                              * use this flag to override that guess.
+                              *
+                              * Note that the by-reference, in-place strategy is
+                              * only used when reusing a compression context
+                              * with compatible compression parameters. (If
+                              * incompatible / uninitialized, the working
+                              * context needs to be cleared anyways, which is
+                              * about as expensive as overwriting it with the
+                              * dictionary context, so there's no savings in
+                              * using the CDict by-ref.)
+                              *
+                              * Values greater than 0 force attaching the dict.
+                              * Values less than 0 force copying the dict.
+                              * 0 selects the default heuristic-guided behavior.
+                              */

 } ZSTD_cParameter;