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1 /*
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2 * jdtrans.c
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3 *
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4 * Copyright (C) 1995-1997, Thomas G. Lane.
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5 * This file is part of the Independent JPEG Group's software.
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6 * For conditions of distribution and use, see the accompanying README file.
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7 *
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8 * This file contains library routines for transcoding decompression,
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9 * that is, reading raw DCT coefficient arrays from an input JPEG file.
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10 * The routines in jdapimin.c will also be needed by a transcoder.
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11 */
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12
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13 #define JPEG_INTERNALS
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14 #include "jinclude.h"
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15 #include "jpeglib.h"
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16
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17
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18 /* Forward declarations */
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19 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
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20
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21
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22 /*
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23 * Read the coefficient arrays from a JPEG file.
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24 * jpeg_read_header must be completed before calling this.
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25 *
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26 * The entire image is read into a set of virtual coefficient-block arrays,
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27 * one per component. The return value is a pointer to the array of
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28 * virtual-array descriptors. These can be manipulated directly via the
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29 * JPEG memory manager, or handed off to jpeg_write_coefficients().
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30 * To release the memory occupied by the virtual arrays, call
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31 * jpeg_finish_decompress() when done with the data.
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32 *
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33 * An alternative usage is to simply obtain access to the coefficient arrays
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34 * during a buffered-image-mode decompression operation. This is allowed
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35 * after any jpeg_finish_output() call. The arrays can be accessed until
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36 * jpeg_finish_decompress() is called. (Note that any call to the library
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37 * may reposition the arrays, so don't rely on access_virt_barray() results
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38 * to stay valid across library calls.)
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39 *
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40 * Returns NULL if suspended. This case need be checked only if
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41 * a suspending data source is used.
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42 */
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43
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44 GLOBAL(jvirt_barray_ptr *)
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45 jpeg_read_coefficients (j_decompress_ptr cinfo)
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46 {
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47 if (cinfo->global_state == DSTATE_READY) {
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48 /* First call: initialize active modules */
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49 transdecode_master_selection(cinfo);
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50 cinfo->global_state = DSTATE_RDCOEFS;
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51 }
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52 if (cinfo->global_state == DSTATE_RDCOEFS) {
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53 /* Absorb whole file into the coef buffer */
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54 for (;;) {
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55 int retcode;
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56 /* Call progress monitor hook if present */
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57 if (cinfo->progress != NULL)
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58 (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
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59 /* Absorb some more input */
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60 retcode = (*cinfo->inputctl->consume_input) (cinfo);
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61 if (retcode == JPEG_SUSPENDED)
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62 return NULL;
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63 if (retcode == JPEG_REACHED_EOI)
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64 break;
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65 /* Advance progress counter if appropriate */
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66 if (cinfo->progress != NULL &&
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67 (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
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68 if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
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69 /* startup underestimated number of scans; ratchet up one scan */
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70 cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
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71 }
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72 }
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73 }
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74 /* Set state so that jpeg_finish_decompress does the right thing */
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75 cinfo->global_state = DSTATE_STOPPING;
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76 }
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77 /* At this point we should be in state DSTATE_STOPPING if being used
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78 * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
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79 * to the coefficients during a full buffered-image-mode decompression.
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80 */
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81 if ((cinfo->global_state == DSTATE_STOPPING ||
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82 cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
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83 return cinfo->coef->coef_arrays;
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84 }
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85 /* Oops, improper usage */
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86 ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
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87 return NULL; /* keep compiler happy */
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88 }
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89
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90
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91 /*
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92 * Master selection of decompression modules for transcoding.
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93 * This substitutes for jdmaster.c's initialization of the full decompressor.
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94 */
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95
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96 LOCAL(void)
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97 transdecode_master_selection (j_decompress_ptr cinfo)
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98 {
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99 /* This is effectively a buffered-image operation. */
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100 cinfo->buffered_image = TRUE;
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101
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102 /* Entropy decoding: either Huffman or arithmetic coding. */
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103 if (cinfo->arith_code) {
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104 ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
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105 } else {
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106 if (cinfo->progressive_mode) {
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107 #ifdef D_PROGRESSIVE_SUPPORTED
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108 jinit_phuff_decoder(cinfo);
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109 #else
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110 ERREXIT(cinfo, JERR_NOT_COMPILED);
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111 #endif
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112 } else
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113 jinit_huff_decoder(cinfo);
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114 }
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115
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116 /* Always get a full-image coefficient buffer. */
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117 jinit_d_coef_controller(cinfo, TRUE);
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118
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119 /* We can now tell the memory manager to allocate virtual arrays. */
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120 (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
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121
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122 /* Initialize input side of decompressor to consume first scan. */
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123 (*cinfo->inputctl->start_input_pass) (cinfo);
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124
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125 /* Initialize progress monitoring. */
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126 if (cinfo->progress != NULL) {
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127 int nscans;
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128 /* Estimate number of scans to set pass_limit. */
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129 if (cinfo->progressive_mode) {
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130 /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
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131 nscans = 2 + 3 * cinfo->num_components;
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132 } else if (cinfo->inputctl->has_multiple_scans) {
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133 /* For a nonprogressive multiscan file, estimate 1 scan per component. */
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134 nscans = cinfo->num_components;
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135 } else {
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136 nscans = 1;
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137 }
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138 cinfo->progress->pass_counter = 0L;
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139 cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
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140 cinfo->progress->completed_passes = 0;
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141 cinfo->progress->total_passes = 1;
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142 }
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143 }
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