From: Nick Terrell <terrelln@fb.com>
Date: Wed, 27 Sep 2017 22:29:07 +0000 (-0700)
Subject: [libzstd][opt] Simplify repcode logic
X-Git-Tag: v1.3.2~3^2~27^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b555b7ef412c6497fa1e806aa91652e852c740aa;p=thirdparty%2Fzstd.git

[libzstd][opt] Simplify repcode logic
---

diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index fd102da2d..c47ce23ad 100644
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -529,7 +529,14 @@ size_t ZSTD_compressBlock_opt_generic(ZSTD_CCtx* ctx,
            } else {
                 opt[cur].rep[2] = (opt[cur].off > 1) ? opt[cur-mlen].rep[1] : opt[cur-mlen].rep[2];
                 opt[cur].rep[1] = (opt[cur].off > 0) ? opt[cur-mlen].rep[0] : opt[cur-mlen].rep[1];
-                opt[cur].rep[0] = ((opt[cur].off==ZSTD_REP_MOVE_OPT) && (mlen != 1)) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
+                /* If opt[cur].off == ZSTD_REP_MOVE_OPT, then mlen != 1.
+                 * offset ZSTD_REP_MOVE_OPT is used for the special case
+                 * litLength == 0, where offset 0 means something special.
+                 * mlen == 1 means the previous byte was stored as a literal,
+                 * so they are mutually exclusive.
+                 */
+                assert(!(opt[cur].off == ZSTD_REP_MOVE_OPT && mlen == 1));
+                opt[cur].rep[0] = (opt[cur].off == ZSTD_REP_MOVE_OPT) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
            }
 
             best_mlen = minMatch;
@@ -804,7 +811,8 @@ size_t ZSTD_compressBlock_opt_extDict_generic(ZSTD_CCtx* ctx,
             } else {
                 opt[cur].rep[2] = (opt[cur].off > 1) ? opt[cur-mlen].rep[1] : opt[cur-mlen].rep[2];
                 opt[cur].rep[1] = (opt[cur].off > 0) ? opt[cur-mlen].rep[0] : opt[cur-mlen].rep[1];
-                opt[cur].rep[0] = ((opt[cur].off==ZSTD_REP_MOVE_OPT) && (mlen != 1)) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
+                assert(!(opt[cur].off == ZSTD_REP_MOVE_OPT && mlen == 1));
+                opt[cur].rep[0] = (opt[cur].off == ZSTD_REP_MOVE_OPT) ? (opt[cur-mlen].rep[0] - 1) : (opt[cur-mlen].rep[opt[cur].off]);
             }
 
             best_mlen = minMatch;