From: Willy Tarreau <w@1wt.eu>
Date: Mon, 10 Dec 2018 12:36:56 +0000 (+0100)
Subject: MINOR: hpack: simplify the len to bytes conversion
X-Git-Tag: v1.9-dev11~131
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1526f1942c1c67cb6c1b82750dbb2e3374b4792f;p=thirdparty%2Fhaproxy.git

MINOR: hpack: simplify the len to bytes conversion

The len-to-bytes conversion can be slightly simplified and optimized
by hardcoding a tree lookup. Just doing this increases by 1% the
request rate on H2. It could be made almost branch-free by using
fls() but it looks overkill for most situations since most headers
are very short.
---

diff --git a/src/hpack-enc.c b/src/hpack-enc.c
index 836584ab41..7c6ef6f800 100644
--- a/src/hpack-enc.c
+++ b/src/hpack-enc.c
@@ -43,13 +43,18 @@
  */
 static inline int len_to_bytes(size_t len)
 {
-	if (len < 127)
+	ssize_t slen = len;
+
+	slen -= 127;
+	if (__builtin_expect(slen < 0, 1))
 		return 1;
-	if (len < 127 + (1 << 7))
-		return 2;
-	if (len < 127 + (1 << 14))
-		return 3;
-	if (len < 127 + (1 << 21))
+	if (slen < (1 << 14)) {
+		if (__builtin_expect(slen < (1 << 7), 1))
+			return 2;
+		else
+			return 3;
+	}
+	if (slen < (1 << 21))
 		return 4;
 	return 0;
 }