From f8bd028dc0a99afeed68e6c3bf28ce6faf3012e2 Mon Sep 17 00:00:00 2001
From: Glenn Strauss <gstrauss@gluelogic.com>
Date: Tue, 25 May 2021 05:04:36 -0400
Subject: [PATCH] [core] http_header_hkey_get() perf (better asm)

---
 src/http_header.c | 48 +++++++++++++++++++++++++++++++----------------
 src/http_header.h |  4 ++--
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/src/http_header.c b/src/http_header.c
index 66609372..dc20e0c0 100644
--- a/src/http_header.c
+++ b/src/http_header.c
@@ -94,25 +94,41 @@ static const keyvlenvalue http_headers[] = {
  ,{ HTTP_HEADER_OTHER, 0, "" }
 };
 
-enum http_header_e http_header_hkey_get(const char * const s, const uint32_t slen) {
-    const struct keyvlenvalue * const kv = http_headers;
-    int i = slen < sizeof(http_headers_off) ? http_headers_off[slen] : -1;
-    if (i < 0) return HTTP_HEADER_OTHER;
-    do {
-        if (buffer_eq_icase_ssn(s, kv[i].value, slen))
-            return (enum http_header_e)kv[i].key;
-    } while (slen == kv[++i].vlen);
+enum http_header_e http_header_hkey_get(const char * const s, const size_t slen) {
+    if (__builtin_expect( (slen < sizeof(http_headers_off)), 1)) {
+        const int i = http_headers_off[slen];
+        /*(lowercase first char as all recognized headers start w/ alpha char)*/
+        const int c = s[0] | 0x20;
+        const struct keyvlenvalue * restrict kv = http_headers + i;
+        if (__builtin_expect( (i != -1), 1)) {
+            do {
+                if (__builtin_expect( (c != kv->value[0]), 1))
+                    continue;
+                if (buffer_eq_icase_ssn(s+1, kv->value+1, slen-1))
+                    return (enum http_header_e)kv->key;
+            } while (slen == (++kv)->vlen);
+        }
+    }
     return HTTP_HEADER_OTHER;
 }
 
-enum http_header_e http_header_hkey_get_lc(const char * const s, const uint32_t slen) {
-    const struct keyvlenvalue * const kv = http_headers;
-    int i = slen < sizeof(http_headers_off) ? http_headers_off[slen] : -1;
-    if (i < 0) return HTTP_HEADER_OTHER;
-    do {
-        if (0 == memcmp(s, kv[i].value, slen))
-            return (enum http_header_e)kv[i].key;
-    } while (slen == kv[++i].vlen);
+enum http_header_e http_header_hkey_get_lc(const char * const s, const size_t slen) {
+    /* XXX: might not provide much real performance over http_header_hkey_get()
+     *      (since the first-char comparision optimization was added)
+     *      (and since well-known h2 headers are already mapped to hkey) */
+    if (__builtin_expect( (slen < sizeof(http_headers_off)), 1)) {
+        const int i = http_headers_off[slen];
+        const int c = s[0];
+        const struct keyvlenvalue * restrict kv = http_headers + i;
+        if (__builtin_expect( (i != -1), 1)) {
+            do {
+                if (__builtin_expect( (c != kv->value[0]), 1))
+                    continue;
+                if (0 == memcmp(s+1, kv->value+1, slen-1))
+                    return (enum http_header_e)kv->key;
+            } while (slen == (++kv)->vlen);
+        }
+    }
     return HTTP_HEADER_OTHER;
 }
 
diff --git a/src/http_header.h b/src/http_header.h
index 0ff5fb46..13731468 100644
--- a/src/http_header.h
+++ b/src/http_header.h
@@ -88,9 +88,9 @@ enum http_header_e {
 };
 
 __attribute_pure__
-enum http_header_e http_header_hkey_get(const char *s, uint32_t slen);
+enum http_header_e http_header_hkey_get(const char *s, size_t slen);
 __attribute_pure__
-enum http_header_e http_header_hkey_get_lc(const char *s, uint32_t slen);
+enum http_header_e http_header_hkey_get_lc(const char *s, size_t slen);
 
 __attribute_pure__
 int http_header_str_to_code (const char * const s);