/* * jdlossls.c * * This file was part of the Independent JPEG Group's software: * Copyright (C) 1998, Thomas G. Lane. * Lossless JPEG Modifications: * Copyright (C) 1999, Ken Murchison. * libjpeg-turbo Modifications: * Copyright (C) 2022, D. R. Commander. * For conditions of distribution and use, see the accompanying README.ijg * file. * * This file contains prediction, sample undifferencing, point transform, and * sample scaling routines for the lossless JPEG decompressor.
*/
/* * In order to avoid a performance penalty for checking which predictor is * being used and which row is being processed for each call of the * undifferencer, and to promote optimization, we have separate undifferencing * functions for each predictor selection value. * * We are able to avoid duplicating source code by implementing the predictors * and undifferencers as macros. Each of the undifferencing functions is * simply a wrapper around an UNDIFFERENCE macro with the appropriate PREDICTOR * macro passed as an argument.
*/
/* Predictor for the first column of the first row: 2^(P-Pt-1) */ #define INITIAL_PREDICTORx (1 << (cinfo->data_precision - cinfo->Al - 1))
/* Predictor for the first column of the remaining rows: Rb */ #define INITIAL_PREDICTOR2 prev_row[0]
/* * 1-Dimensional undifferencer routine. * * This macro implements the 1-D horizontal predictor (1). INITIAL_PREDICTOR * is used as the special case predictor for the first column, which must be * either INITIAL_PREDICTOR2 or INITIAL_PREDICTORx. The remaining samples * use PREDICTOR1. * * The reconstructed sample is supposed to be calculated modulo 2^16, so we * logically AND the result with 0xFFFF.
*/
#define UNDIFFERENCE_1D(INITIAL_PREDICTOR) \ int Ra; \
\
Ra = (*diff_buf++ + INITIAL_PREDICTOR) & 0xFFFF; \
*undiff_buf++ = Ra; \
\ while (--width) { \
Ra = (*diff_buf++ + PREDICTOR1) & 0xFFFF; \
*undiff_buf++ = Ra; \
}
/* * 2-Dimensional undifferencer routine. * * This macro implements the 2-D horizontal predictors (#2-7). PREDICTOR2 is * used as the special case predictor for the first column. The remaining * samples use PREDICTOR, which is a function of Ra, Rb, and Rc. * * Because prev_row and output_buf may point to the same storage area (in an * interleaved image with Vi=1, for example), we must take care to buffer Rb/Rc * before writing the current reconstructed sample value into output_buf. * * The reconstructed sample is supposed to be calculated modulo 2^16, so we * logically AND the result with 0xFFFF.
*/
/* * Undifferencers for the second and subsequent rows in a scan or restart * interval. The first sample in the row is undifferenced using the vertical * predictor (2). The rest of the samples are undifferenced using the * predictor specified in the scan header.
*/
/* * Undifferencer for the first row in a scan or restart interval. The first * sample in the row is undifferenced using the special predictor constant * x=2^(P-Pt-1). The rest of the samples are undifferenced using the * 1-D horizontal predictor (1).
*/
/* * Now that we have undifferenced the first row, we want to use the * undifferencer that corresponds to the predictor specified in the * scan header.
*/ switch (cinfo->Ss) { case 1:
losslessd->predict_undifference[comp_index] = jpeg_undifference1; break; case 2:
losslessd->predict_undifference[comp_index] = jpeg_undifference2; break; case 3:
losslessd->predict_undifference[comp_index] = jpeg_undifference3; break; case 4:
losslessd->predict_undifference[comp_index] = jpeg_undifference4; break; case 5:
losslessd->predict_undifference[comp_index] = jpeg_undifference5; break; case 6:
losslessd->predict_undifference[comp_index] = jpeg_undifference6; break; case 7:
losslessd->predict_undifference[comp_index] = jpeg_undifference7; break;
}
}
/*********************** Sample upscaling by 2^Pt ************************/
METHODDEF(void)
noscale(j_decompress_ptr cinfo,
JDIFFROW diff_buf, _JSAMPROW output_buf, JDIMENSION width)
{ do {
*output_buf++ = (_JSAMPLE)(*diff_buf++);
} while (--width);
}
/* * Initialize for an input processing pass.
*/
METHODDEF(void)
start_pass_lossless(j_decompress_ptr cinfo)
{
lossless_decomp_ptr losslessd = (lossless_decomp_ptr)cinfo->idct; int ci;
/* Check that the scan parameters Ss, Se, Ah, Al are OK for lossless JPEG. * * Ss is the predictor selection value (psv). Legal values for sequential * lossless JPEG are: 1 <= psv <= 7. * * Se and Ah are not used and should be zero. * * Al specifies the point transform (Pt). * Legal values are: 0 <= Pt <= (data precision - 1).
*/ if (cinfo->Ss < 1 || cinfo->Ss > 7 ||
cinfo->Se != 0 || cinfo->Ah != 0 ||
cinfo->Al < 0 || cinfo->Al >= cinfo->data_precision)
ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
/* Set undifference functions to first row function */ for (ci = 0; ci < cinfo->num_components; ci++)
losslessd->predict_undifference[ci] = jpeg_undifference_first_row;
/* Set scaler function based on Pt */ if (cinfo->Al)
losslessd->scaler_scale = simple_upscale; else
losslessd->scaler_scale = noscale;
}
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