[PATCH 06/13] CryptoPkg/TlsLib: use binary search in the TlsGetCipherMapping() function

[Laszlo Ersek <lersek@redhat.com>]

Improve the performance of the TlsGetCipherMapping() function by adopting
the binary search from DhcpFindOptionFormat()
[MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Option.c].

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Qin Long <qin.long@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Ting Ye <ting.ye@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=915
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 CryptoPkg/Library/TlsLib/TlsConfig.c | 36 +++++++++++++-------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/CryptoPkg/Library/TlsLib/TlsConfig.c b/CryptoPkg/Library/TlsLib/TlsConfig.c
index 507489386b8e..c1d91a599482 100644
--- a/CryptoPkg/Library/TlsLib/TlsConfig.c
+++ b/CryptoPkg/Library/TlsLib/TlsConfig.c
@@ -27,12 +27,14 @@ typedef struct {
 } TLS_CIPHER_MAPPING;
 
 //
 // The mapping table between IANA/IETF Cipher Suite definitions and
 // OpenSSL-used Cipher Suite name.
 //
+// Keep the table uniquely sorted by the IanaCipher field, in increasing order.
+//
 STATIC CONST TLS_CIPHER_MAPPING TlsCipherMappingTable[] = {
   { 0x0001, "NULL-MD5" },                 /// TLS_RSA_WITH_NULL_MD5
   { 0x0002, "NULL-SHA" },                 /// TLS_RSA_WITH_NULL_SHA
   { 0x0004, "RC4-MD5" },                  /// TLS_RSA_WITH_RC4_128_MD5
   { 0x0005, "RC4-SHA" },                  /// TLS_RSA_WITH_RC4_128_SHA
   { 0x000A, "DES-CBC3-SHA" },             /// TLS_RSA_WITH_3DES_EDE_CBC_SHA, mandatory TLS 1.1
@@ -68,28 +70,36 @@ STATIC CONST TLS_CIPHER_MAPPING TlsCipherMappingTable[] = {
 STATIC
 CONST TLS_CIPHER_MAPPING *
 TlsGetCipherMapping (
   IN     UINT16                   CipherId
   )
 {
-  CONST TLS_CIPHER_MAPPING  *CipherEntry;
-  UINTN                     TableSize;
-  UINTN                     Index;
-
-  CipherEntry = TlsCipherMappingTable;
-  TableSize = sizeof (TlsCipherMappingTable) / sizeof (TLS_CIPHER_MAPPING);
+  INTN                      Left;
+  INTN                      Right;
+  INTN                      Middle;
 
   //
-  // Search Cipher Mapping Table for IANA-OpenSSL Cipher Translation
+  // Binary Search Cipher Mapping Table for IANA-OpenSSL Cipher Translation
   //
-  for (Index = 0; Index < TableSize; Index++, CipherEntry++) {
-    //
-    // Translate IANA cipher suite name to OpenSSL name.
-    //
-    if (CipherEntry->IanaCipher == CipherId) {
-      return CipherEntry;
+  Left  = 0;
+  Right = ARRAY_SIZE (TlsCipherMappingTable) - 1;
+
+  while (Right >= Left) {
+    Middle = (Left + Right) / 2;
+
+    if (CipherId == TlsCipherMappingTable[Middle].IanaCipher) {
+      //
+      // Translate IANA cipher suite ID to OpenSSL name.
+      //
+      return &TlsCipherMappingTable[Middle];
+    }
+
+    if (CipherId < TlsCipherMappingTable[Middle].IanaCipher) {
+      Right = Middle - 1;
+    } else {
+      Left  = Middle + 1;
     }
   }
 
   //
   // No Cipher Mapping found, return NULL.
   //
-- 
2.14.1.3.gb7cf6e02401b