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/*
* 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
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