From: senhuang42 <senhuang96@fb.com>
Date: Thu, 19 Nov 2020 16:56:16 +0000 (-0500)
Subject: Unroll isRLE loop
X-Git-Tag: v1.4.7~31^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dcbbf7c09fb293920cf938fe149c8c238ae2f74c;p=thirdparty%2Fzstd.git

Unroll isRLE loop
---

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index c21a8c982..cfe784f5f 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -2586,12 +2586,27 @@ size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t seqsSize) {
     return out;
 }
 
-/* Returns true if the given block is a RLE block */
-static int ZSTD_isRLE(const BYTE *ip, size_t length) {
+/* Unrolled loop to read four size_ts of input at a time. Returns 1 if is RLE, 0 if not. */
+static int ZSTD_isRLE(const BYTE* src, size_t length) {
+    const BYTE* ip = src;
+    const BYTE value = ip[0];
+    const size_t valueST = value * 0x0101010101010101ULL;
+    const size_t unrollSize = sizeof(size_t) * 4;
+    const size_t unrollMask = unrollSize - 1;
+    const size_t prefixLength = length & unrollMask;
     size_t i;
-    if (length < 2) return 1;
-    for (i = 1; i < length; ++i) {
-        if (ip[0] != ip[i]) return 0;
+    size_t u;
+    if (length == 1) return 1;
+    /* Check if prefix is RLE first before using unrolled loop */
+    if (prefixLength && ZSTD_count(ip+1, ip, ip+prefixLength) != prefixLength-1) {
+        return 0;
+    }
+    for (i = prefixLength; i != length; i += unrollSize) {
+        for (u = 0; u < unrollSize; u += sizeof(size_t)) {
+            if (MEM_readST(ip + i + u) != valueST) {
+                return 0;
+            }
+        }
     }
     return 1;
 }