The Independent JPEG Group's JPEG software v1

1 files changed, 146 insertions, 0 deletions

diff --git a/jdmcu.c b/jdmcu.c
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+/*
+ * jdmcu.c
+ *
+ * Copyright (C) 1991, Thomas G. Lane.
+ * This file is part of the Independent JPEG Group's software.
+ * For conditions of distribution and use, see the accompanying README file.
+ *
+ * This file contains MCU disassembly routines and quantization descaling.
+ * These routines are invoked via the disassemble_MCU and
+ * disassemble_init/term methods.
+ */
+
+#include "jinclude.h"
+
+
+/*
+ * Quantization descaling and zigzag reordering
+ */
+
+
+/* ZAG[i] is the natural-order position of the i'th element of zigzag order. */
+
+static const short ZAG[DCTSIZE2] = {
+  0,  1,  8, 16,  9,  2,  3, 10,
+ 17, 24, 32, 25, 18, 11,  4,  5,
+ 12, 19, 26, 33, 40, 48, 41, 34,
+ 27, 20, 13,  6,  7, 14, 21, 28,
+ 35, 42, 49, 56, 57, 50, 43, 36,
+ 29, 22, 15, 23, 30, 37, 44, 51,
+ 58, 59, 52, 45, 38, 31, 39, 46,
+ 53, 60, 61, 54, 47, 55, 62, 63
+};
+
+
+LOCAL void
+qdescale_zig (JBLOCK input, JBLOCKROW outputptr, QUANT_TBL_PTR quanttbl)
+{
+  short i;
+
+  for (i = 0; i < DCTSIZE2; i++) {
+    (*outputptr)[ZAG[i]] = (*input++) * (*quanttbl++);
+  }
+}
+
+
+
+/*
+ * Fetch one MCU row from entropy_decode, build coefficient array.
+ * This version is used for noninterleaved (single-component) scans.
+ */
+
+METHODDEF void
+disassemble_noninterleaved_MCU (decompress_info_ptr cinfo,
+				JBLOCKIMAGE image_data)
+{
+  JBLOCK MCU_data[1];
+  long mcuindex;
+  jpeg_component_info * compptr;
+  QUANT_TBL_PTR quant_ptr;
+
+  /* this is pretty easy since there is one component and one block per MCU */
+  compptr = cinfo->cur_comp_info[0];
+  quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
+  for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
+    /* Fetch the coefficient data */
+    (*cinfo->methods->entropy_decode) (cinfo, MCU_data);
+    /* Descale, reorder, and distribute it into the image array */
+    qdescale_zig(MCU_data[0], image_data[0][0] + mcuindex, quant_ptr);
+  }
+}
+
+
+/*
+ * Fetch one MCU row from entropy_decode, build coefficient array.
+ * This version is used for interleaved (multi-component) scans.
+ */
+
+METHODDEF void
+disassemble_interleaved_MCU (decompress_info_ptr cinfo,
+			     JBLOCKIMAGE image_data)
+{
+  JBLOCK MCU_data[MAX_BLOCKS_IN_MCU];
+  long mcuindex;
+  short blkn, ci, xpos, ypos;
+  jpeg_component_info * compptr;
+  QUANT_TBL_PTR quant_ptr;
+  JBLOCKROW image_ptr;
+
+  for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
+    /* Fetch the coefficient data */
+    (*cinfo->methods->entropy_decode) (cinfo, MCU_data);
+    /* Descale, reorder, and distribute it into the image array */
+    blkn = 0;
+    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+      compptr = cinfo->cur_comp_info[ci];
+      quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
+      for (ypos = 0; ypos < compptr->MCU_height; ypos++) {
+	image_ptr = image_data[ci][ypos] + (mcuindex * compptr->MCU_width);
+	for (xpos = 0; xpos < compptr->MCU_width; xpos++) {
+	  qdescale_zig(MCU_data[blkn], image_ptr, quant_ptr);
+	  image_ptr++;
+	  blkn++;
+	}
+      }
+    }
+  }
+}
+
+
+/*
+ * Initialize for processing a scan.
+ */
+
+METHODDEF void
+disassemble_init (decompress_info_ptr cinfo)
+{
+  /* no work for now */
+}
+
+
+/*
+ * Clean up after a scan.
+ */
+
+METHODDEF void
+disassemble_term (decompress_info_ptr cinfo)
+{
+  /* no work for now */
+}
+
+
+
+/*
+ * The method selection routine for MCU disassembly.
+ */
+
+GLOBAL void
+jseldmcu (decompress_info_ptr cinfo)
+{
+  if (cinfo->comps_in_scan == 1)
+    cinfo->methods->disassemble_MCU = disassemble_noninterleaved_MCU;
+  else
+    cinfo->methods->disassemble_MCU = disassemble_interleaved_MCU;
+  cinfo->methods->disassemble_init = disassemble_init;
+  cinfo->methods->disassemble_term = disassemble_term;
+}