Scan from start of buffer to handle case where an invalid size was passed.

BUG=404
TESTED=libyuvTest.ValidateJpegLarge
R=brucedawson@google.com, harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/41989004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1285 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1284
+Version: 1285
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1284
+#define LIBYUV_VERSION 1285
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

source/mjpeg_validate.cc

@@ -10,15 +10,66 @@
 
 #include "libyuv/mjpeg_decoder.h"
 
+#include <string.h>  // For memchr.
+
 #ifdef __cplusplus
 namespace libyuv {
 extern "C" {
 #endif
 
+// Enable this to try scasb implementation.
+// #define ENABLE_SCASB 1
+
+#ifdef ENABLE_SCASB
+
+// Multiple of 1.
+__declspec(naked) __declspec(align(16))
+const uint8* ScanRow_ERMS(const uint8* src, uint32 val, int count) {
+  __asm {
+    mov        edx, edi
+    mov        edi, [esp + 4]   // src
+    mov        eax, [esp + 8]   // val
+    mov        ecx, [esp + 12]  // count
+    repne scasb
+    jne        sr99
+    mov        eax, edi
+    sub        eax, 1
+    mov        edi, edx
+    ret
+
+  sr99:
+    mov        eax, 0
+    mov        edi, edx
+    ret
+  }
+}
+#endif
+
+// Helper function to scan for EOI marker.
+static LIBYUV_BOOL ScanEOI(const uint8* sample, size_t sample_size) {
+  const uint8* end = sample + sample_size - 1;
+  const uint8* it = sample;
+  for (;;) {
+#ifdef ENABLE_SCASB
+    it = ScanRow_ERMS(it, 0xff, end - it);
+#else
+    it = static_cast<const uint8*>(memchr(it, 0xff, end - it));
+#endif
+    if (it == NULL) {
+      break;
+    }
+    if (it[1] == 0xd9) {
+      return LIBYUV_TRUE;  // Success: Valid jpeg.
+    }
+    ++it;  // Skip over current 0xff.
+  }
+  // ERROR: Invalid jpeg end code not found. Size sample_size
+  return LIBYUV_FALSE;
+}
+
 // Helper function to validate the jpeg appears intact.
-// TODO(fbarchard): Optimize case where SOI is found but EOI is not.
 LIBYUV_BOOL ValidateJpeg(const uint8* sample, size_t sample_size) {
-  size_t i;
+  const size_t kBackSearchSize = 1024;
   if (sample_size < 64) {
     // ERROR: Invalid jpeg size: sample_size
     return LIBYUV_FALSE;
@@ -27,17 +78,20 @@ LIBYUV_BOOL ValidateJpeg(const uint8* sample, size_t sample_size) {
     // ERROR: Invalid jpeg initial start code
     return LIBYUV_FALSE;
   }
-  for (i = sample_size - 2; i > 1;) {
-    if (sample[i] != 0xd9) {
-      if (sample[i] == 0xff && sample[i + 1] == 0xd9) {  // End Of Image
+  // Step over SOI marker.
+  sample += 2;
+  sample_size -= 2;
+
+  // Look for the End Of Image (EOI) marker in the end kilobyte of the buffer.
+  if (sample_size > kBackSearchSize) {
+    if (ScanEOI(sample + sample_size - kBackSearchSize, kBackSearchSize)) {
       return LIBYUV_TRUE;  // Success: Valid jpeg.
     }
-      --i;
-    }
-    --i;
+    // Reduce search size for forward search.
+    sample_size = sample_size - kBackSearchSize + 1;
   }
-  // ERROR: Invalid jpeg end code not found. Size sample_size
-  return LIBYUV_FALSE;
+  return ScanEOI(sample, sample_size);
+
 }
 
 #ifdef __cplusplus

unit_test/convert_test.cc

@@ -1035,7 +1035,8 @@ TEST_F(libyuvTest, ValidateJpegLarge) {
   const int kImageSize = benchmark_width_ * benchmark_height_ >= kMinJpeg ?
     benchmark_width_ * benchmark_height_ : kMinJpeg;
   const int kSize = kImageSize + kOff;
-  const int kBufSize = kImageSize * 10 + kOff;
+  const int kMultiple = 10;
+  const int kBufSize = kImageSize * kMultiple + kOff;
   align_buffer_64(orig_pixels, kBufSize);
 
   // No SOI or EOI. Expect fail.