1/* 2 * Copyright 2012 The LibYuv Project Authors. All rights reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11#include "libyuv/mjpeg_decoder.h" 12 13#include <string.h> // For memchr. 14 15#ifdef __cplusplus 16namespace libyuv { 17extern "C" { 18#endif 19 20// Enable this to try scasb implementation. 21// #define ENABLE_SCASB 1 22 23#ifdef ENABLE_SCASB 24 25// Multiple of 1. 26__declspec(naked) 27const uint8* ScanRow_ERMS(const uint8* src, uint32 val, int count) { 28 __asm { 29 mov edx, edi 30 mov edi, [esp + 4] // src 31 mov eax, [esp + 8] // val 32 mov ecx, [esp + 12] // count 33 repne scasb 34 jne sr99 35 mov eax, edi 36 sub eax, 1 37 mov edi, edx 38 ret 39 40 sr99: 41 mov eax, 0 42 mov edi, edx 43 ret 44 } 45} 46#endif 47 48// Helper function to scan for EOI marker. 49static LIBYUV_BOOL ScanEOI(const uint8* sample, size_t sample_size) { 50 const uint8* end = sample + sample_size - 1; 51 const uint8* it = sample; 52 for (;;) { 53#ifdef ENABLE_SCASB 54 it = ScanRow_ERMS(it, 0xff, end - it); 55#else 56 it = static_cast<const uint8*>(memchr(it, 0xff, end - it)); 57#endif 58 if (it == NULL) { 59 break; 60 } 61 if (it[1] == 0xd9) { 62 return LIBYUV_TRUE; // Success: Valid jpeg. 63 } 64 ++it; // Skip over current 0xff. 65 } 66 // ERROR: Invalid jpeg end code not found. Size sample_size 67 return LIBYUV_FALSE; 68} 69 70// Helper function to validate the jpeg appears intact. 71LIBYUV_BOOL ValidateJpeg(const uint8* sample, size_t sample_size) { 72 const size_t kBackSearchSize = 1024; 73 if (sample_size < 64) { 74 // ERROR: Invalid jpeg size: sample_size 75 return LIBYUV_FALSE; 76 } 77 if (sample[0] != 0xff || sample[1] != 0xd8) { // Start Of Image 78 // ERROR: Invalid jpeg initial start code 79 return LIBYUV_FALSE; 80 } 81 // Step over SOI marker. 82 sample += 2; 83 sample_size -= 2; 84 85 // Look for the End Of Image (EOI) marker in the end kilobyte of the buffer. 86 if (sample_size > kBackSearchSize) { 87 if (ScanEOI(sample + sample_size - kBackSearchSize, kBackSearchSize)) { 88 return LIBYUV_TRUE; // Success: Valid jpeg. 89 } 90 // Reduce search size for forward search. 91 sample_size = sample_size - kBackSearchSize + 1; 92 } 93 return ScanEOI(sample, sample_size); 94 95} 96 97#ifdef __cplusplus 98} // extern "C" 99} // namespace libyuv 100#endif 101 102