ref: 5bd99f83d9dc1269c4413766d856c41ea25e3931
dir: /third_party/libyuv/source/mjpeg_validate.cc/
/* * Copyright 2012 The LibYuv Project Authors. All rights reserved. * * Use of this source code is governed by a BSD-style license * that can be found in the LICENSE file in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. */ #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) 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. LIBYUV_BOOL ValidateJpeg(const uint8* sample, size_t sample_size) { const size_t kBackSearchSize = 1024; if (sample_size < 64) { // ERROR: Invalid jpeg size: sample_size return LIBYUV_FALSE; } if (sample[0] != 0xff || sample[1] != 0xd8) { // Start Of Image // ERROR: Invalid jpeg initial start code return LIBYUV_FALSE; } // 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. } // Reduce search size for forward search. sample_size = sample_size - kBackSearchSize + 1; } return ScanEOI(sample, sample_size); } #ifdef __cplusplus } // extern "C" } // namespace libyuv #endif