-/*
- * Save away a copy of the Q-table referenced by each component present
- * in the current scan, unless already saved during a prior scan.
- *
- * In a multiple-scan JPEG file, the encoder could assign different components
- * the same Q-table slot number, but change table definitions between scans
- * so that each component uses a different Q-table. (The IJG encoder is not
- * currently capable of doing this, but other encoders might.) Since we want
- * to be able to dequantize all the components at the end of the file, this
- * means that we have to save away the table actually used for each component.
- * We do this by copying the table at the start of the first scan containing
- * the component.
- * The JPEG spec prohibits the encoder from changing the contents of a Q-table
- * slot between scans of a component using that slot. If the encoder does so
- * anyway, this decoder will simply use the Q-table values that were current
- * at the start of the first scan for the component.
- *
- * The decompressor output side looks only at the saved quant tables,
- * not at the current Q-table slots.
- */
-
-LOCAL(void)
-latch_quant_tables (j_decompress_ptr cinfo)
-{
- int ci, qtblno;
- jpeg_component_info *compptr;
- JQUANT_TBL * qtbl;
-
- for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
- compptr = cinfo->cur_comp_info[ci];
- /* No work if we already saved Q-table for this component */
- if (compptr->quant_table != NULL)
- continue;
- /* Make sure specified quantization table is present */
- qtblno = compptr->quant_tbl_no;
- if (qtblno < 0 || qtblno >= NUM_QUANT_TBLS ||
- cinfo->quant_tbl_ptrs[qtblno] == NULL)
- ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, qtblno);
- /* OK, save away the quantization table */
- qtbl = (JQUANT_TBL *)
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- SIZEOF(JQUANT_TBL));
- MEMCOPY(qtbl, cinfo->quant_tbl_ptrs[qtblno], SIZEOF(JQUANT_TBL));
- compptr->quant_table = qtbl;
- }
-}
-
-