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