path: root/jbig2dec/jbig2_text.c

/* Copyright (C) 2001-2019 Artifex Software, Inc.
   All Rights Reserved.

   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied,
   modified or distributed except as expressly authorized under the terms
   of the license contained in the file LICENSE in this distribution.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
   CA 94945, U.S.A., +1(415)492-9861, for further information.
*/

/*
    jbig2dec
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "os_types.h"

#include <stddef.h>
#include <string.h>             /* memset() */

#include "jbig2.h"
#include "jbig2_priv.h"
#include "jbig2_arith.h"
#include "jbig2_arith_int.h"
#include "jbig2_arith_iaid.h"
#include "jbig2_generic.h"
#include "jbig2_huffman.h"
#include "jbig2_image.h"
#include "jbig2_page.h"
#include "jbig2_refinement.h"
#include "jbig2_segment.h"
#include "jbig2_symbol_dict.h"
#include "jbig2_text.h"

/**
 * jbig2_decode_text_region: decode a text region segment
 *
 * @ctx: jbig2 decoder context
 * @segment: jbig2 segment (header) structure
 * @params: parameters from the text region header
 * @dicts: an array of referenced symbol dictionaries
 * @n_dicts: the number of referenced symbol dictionaries
 * @image: image structure in which to store the decoded region bitmap
 * @data: pointer to text region data to be decoded
 * @size: length of text region data
 *
 * Implements the text region decoding procedure
 * described in section 6.4 of the JBIG2 spec.
 *
 * returns: 0 on success
 **/
int
jbig2_decode_text_region(Jbig2Ctx *ctx, Jbig2Segment *segment,
                         const Jbig2TextRegionParams *params,
                         const Jbig2SymbolDict *const *dicts, const uint32_t n_dicts,
                         Jbig2Image *image, const byte *data, const size_t size, Jbig2ArithCx *GR_stats, Jbig2ArithState *as, Jbig2WordStream *ws)
{
    /* relevant bits of 6.4.4 */
    uint32_t NINSTANCES;
    uint32_t ID;
    int32_t STRIPT;
    int32_t FIRSTS;
    int32_t DT;
    int32_t DFS;
    int32_t IDS;
    int32_t CURS;
    int32_t CURT;
    int S, T;
    int x, y;
    bool first_symbol;
    uint32_t index, SBNUMSYMS;
    Jbig2Image *IB = NULL;
    Jbig2Image *IBO = NULL;
    Jbig2Image *refimage = NULL;
    Jbig2HuffmanState *hs = NULL;
    Jbig2HuffmanTable *SBSYMCODES = NULL;
    int code = 0;
    int RI;

    SBNUMSYMS = 0;
    for (index = 0; index < n_dicts; index++) {
        SBNUMSYMS += dicts[index]->n_symbols;
    }
    jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "symbol list contains %d glyphs in %d dictionaries", SBNUMSYMS, n_dicts);

    if (params->SBHUFF) {
        Jbig2HuffmanTable *runcodes = NULL;
        Jbig2HuffmanParams runcodeparams;
        Jbig2HuffmanLine runcodelengths[35];
        Jbig2HuffmanLine *symcodelengths = NULL;
        Jbig2HuffmanParams symcodeparams;
        int err, len, range, r;

        jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "huffman coded text region");
        hs = jbig2_huffman_new(ctx, ws);
        if (hs == NULL)
            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region");

        /* 7.4.3.1.7 - decode symbol ID Huffman table */
        /* this is actually part of the segment header, but it is more
           convenient to handle it here */

        /* parse and build the runlength code huffman table */
        for (index = 0; index < 35; index++) {
            runcodelengths[index].PREFLEN = jbig2_huffman_get_bits(hs, 4, &code);
            if (code < 0) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to read huffman runcode lengths");
                goto cleanup1;
            }
            if (code > 0) {
                jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB decoding huffman runcode lengths");
                goto cleanup1;
            }
            runcodelengths[index].RANGELEN = 0;
            runcodelengths[index].RANGELOW = index;
            jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "  read runcode%d length %d", index, runcodelengths[index].PREFLEN);
        }
        runcodeparams.HTOOB = 0;
        runcodeparams.lines = runcodelengths;
        runcodeparams.n_lines = 35;
        runcodes = jbig2_build_huffman_table(ctx, &runcodeparams);
        if (runcodes == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "error constructing symbol ID runcode table");
            goto cleanup1;
        }

        /* decode the symbol ID code lengths using the runlength table */
        symcodelengths = jbig2_new(ctx, Jbig2HuffmanLine, SBNUMSYMS);
        if (symcodelengths == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "failed to allocate memory when reading symbol ID huffman table");
            goto cleanup1;
        }
        index = 0;
        while (index < SBNUMSYMS) {
            code = jbig2_huffman_get(hs, runcodes, &err);
            if (err < 0) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "error reading symbol ID huffman table");
                goto cleanup1;
            }
            if (err > 0) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB decoding symbol ID huffman table");
                goto cleanup1;
            }
            if (code < 0 || code >= 35) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "symbol ID huffman table out of range");
                goto cleanup1;
            }

            if (code < 32) {
                len = code;
                range = 1;
            } else {
                if (code == 32) {
                    if (index < 1) {
                        code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "error decoding symbol ID table: run length with no antecedent");
                        goto cleanup1;
                    }
                    len = symcodelengths[index - 1].PREFLEN;
                } else {
                    len = 0;    /* code == 33 or 34 */
                }
                err = 0;
                if (code == 32)
                    range = jbig2_huffman_get_bits(hs, 2, &err) + 3;
                else if (code == 33)
                    range = jbig2_huffman_get_bits(hs, 3, &err) + 3;
                else if (code == 34)
                    range = jbig2_huffman_get_bits(hs, 7, &err) + 11;
                if (err < 0) {
                    code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to read huffman code");
                    goto cleanup1;
                }
                if (err > 0) {
                    code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB decoding huffman code");
                    goto cleanup1;
                }
            }
            jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "  read runcode%d at index %d (length %d range %d)", code, index, len, range);
            if (index + range > SBNUMSYMS) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number,
                            "runlength extends %d entries beyond the end of symbol ID table", index + range - SBNUMSYMS);
                range = SBNUMSYMS - index;
            }
            for (r = 0; r < range; r++) {
                symcodelengths[index + r].PREFLEN = len;
                symcodelengths[index + r].RANGELEN = 0;
                symcodelengths[index + r].RANGELOW = index + r;
            }
            index += r;
        }

        if (index < SBNUMSYMS) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "runlength codes do not cover the available symbol set");
            goto cleanup1;
        }

        symcodeparams.HTOOB = 0;
        symcodeparams.lines = symcodelengths;
        symcodeparams.n_lines = SBNUMSYMS;

        /* skip to byte boundary */
        err = jbig2_huffman_skip(hs);
        if (err < 0)
        {
            jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to skip to next byte when building huffman table");
            goto cleanup1;
        }

        /* finally, construct the symbol ID huffman table itself */
        SBSYMCODES = jbig2_build_huffman_table(ctx, &symcodeparams);

cleanup1:
        jbig2_free(ctx->allocator, symcodelengths);
        jbig2_release_huffman_table(ctx, runcodes);

        if (SBSYMCODES == NULL) {
            jbig2_huffman_free(ctx, hs);
            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to construct symbol ID huffman table");
        }
    }

    /* 6.4.5 (1) */
    jbig2_image_clear(ctx, image, params->SBDEFPIXEL);

    /* 6.4.6 */
    if (params->SBHUFF) {
        STRIPT = jbig2_huffman_get(hs, params->SBHUFFDT, &code);
    } else {
        code = jbig2_arith_int_decode(ctx, params->IADT, as, &STRIPT);
    }
    if (code < 0) {
        jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode strip T");
        goto cleanup2;
    }
    if (code > 0) {
        code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding strip T");
        goto cleanup2;
    }

    /* 6.4.5 (2) */
    STRIPT *= -(params->SBSTRIPS);
    FIRSTS = 0;
    NINSTANCES = 0;

    /* 6.4.5 (3) */
    while (NINSTANCES < params->SBNUMINSTANCES) {
        /* (3b) */
        if (params->SBHUFF) {
            DT = jbig2_huffman_get(hs, params->SBHUFFDT, &code);
        } else {
            code = jbig2_arith_int_decode(ctx, params->IADT, as, &DT);
        }
        if (code < 0) {
            jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode delta T");
            goto cleanup2;
        }
        if (code > 0) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding delta T");
            goto cleanup2;
        }
        DT *= params->SBSTRIPS;
        STRIPT += DT;

        first_symbol = TRUE;
        /* 6.4.5 (3c) - decode symbols in strip */
        for (;;) {
            /* (3c.i) */
            if (first_symbol) {
                /* 6.4.7 */
                if (params->SBHUFF) {
                    DFS = jbig2_huffman_get(hs, params->SBHUFFFS, &code);
                } else {
                    code = jbig2_arith_int_decode(ctx, params->IAFS, as, &DFS);
                }
                if (code < 0) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode strip symbol S-difference");
                    goto cleanup2;
                }
                if (code > 0) {
                    code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding strip symbol S-difference");
                    goto cleanup2;
                }
                FIRSTS += DFS;
                CURS = FIRSTS;
                first_symbol = FALSE;
            } else {
                if (NINSTANCES > params->SBNUMINSTANCES) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "too many NINSTANCES (%d) decoded", NINSTANCES);
                    break;
                }
                /* (3c.ii) / 6.4.8 */
                if (params->SBHUFF) {
                    IDS = jbig2_huffman_get(hs, params->SBHUFFDS, &code);
                } else {
                    code = jbig2_arith_int_decode(ctx, params->IADS, as, &IDS);
                }
                if (code < 0) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode symbol instance S coordinate");
                    goto cleanup2;
                }
                if (code > 0) {
                    jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "OOB obtained when decoding symbol instance S coordinate signals end of strip with T value %d", DT);
                    break;
                }
                CURS += IDS + params->SBDSOFFSET;
            }

            /* (3c.iii) / 6.4.9 */
            if (params->SBSTRIPS == 1) {
                CURT = 0;
            } else if (params->SBHUFF) {
                CURT = jbig2_huffman_get_bits(hs, params->LOGSBSTRIPS, &code);
            } else {
                code = jbig2_arith_int_decode(ctx, params->IAIT, as, &CURT);
            }
            if (code < 0) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode symbol instance T coordinate");
                goto cleanup2;
            }
            if (code > 0) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "OOB obtained when decoding symbol instance T coordinate");
                goto cleanup2;
            }
            T = STRIPT + CURT;

            /* (3b.iv) / 6.4.10 - decode the symbol ID */
            if (params->SBHUFF) {
                ID = jbig2_huffman_get(hs, SBSYMCODES, &code);
            } else {
                code = jbig2_arith_iaid_decode(ctx, params->IAID, as, (int *)&ID);
            }
            if (code < 0) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to obtain symbol instance symbol ID");
                goto cleanup2;
            }
            if (code > 0) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding symbol instance symbol ID");
                goto cleanup2;
            }
            if (ID >= SBNUMSYMS) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "ignoring out of range symbol ID (%d/%d)", ID, SBNUMSYMS);
                IB = NULL;
            } else {
                /* (3c.v) / 6.4.11 - look up the symbol bitmap IB */
                uint32_t id = ID;

                index = 0;
                while (id >= dicts[index]->n_symbols)
                    id -= dicts[index++]->n_symbols;
                if (dicts[index]->glyphs[id] == NULL) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "missing glyph (%d/%d), ignoring", index, id);
                } else {
                    IB = jbig2_image_reference(ctx, dicts[index]->glyphs[id]);
                }
            }
            if (params->SBREFINE) {
                if (params->SBHUFF) {
                    RI = jbig2_huffman_get_bits(hs, 1, &code);
                } else {
                    code = jbig2_arith_int_decode(ctx, params->IARI, as, &RI);
                }
                if (code < 0) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode symbol bitmap refinement indicator");
                    goto cleanup2;
                }
                if (code > 0) {
                    code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding symbol bitmap refinement indicator");
                    goto cleanup2;
                }
            } else {
                RI = 0;
            }
            if (RI) {
                Jbig2RefinementRegionParams rparams;
                int32_t RDW, RDH, RDX, RDY;
                size_t BMSIZE = 0;
                int code1 = 0;
                int code2 = 0;
                int code3 = 0;
                int code4 = 0;
                int code5 = 0;
                int code6 = 0;

                /* 6.4.11 (1, 2, 3, 4) */
                if (!params->SBHUFF) {
                    code1 = jbig2_arith_int_decode(ctx, params->IARDW, as, &RDW);
                    code2 = jbig2_arith_int_decode(ctx, params->IARDH, as, &RDH);
                    code3 = jbig2_arith_int_decode(ctx, params->IARDX, as, &RDX);
                    code4 = jbig2_arith_int_decode(ctx, params->IARDY, as, &RDY);
                } else {
                    RDW = jbig2_huffman_get(hs, params->SBHUFFRDW, &code1);
                    RDH = jbig2_huffman_get(hs, params->SBHUFFRDH, &code2);
                    RDX = jbig2_huffman_get(hs, params->SBHUFFRDX, &code3);
                    RDY = jbig2_huffman_get(hs, params->SBHUFFRDY, &code4);
                    BMSIZE = jbig2_huffman_get(hs, params->SBHUFFRSIZE, &code5);
                    code6 = jbig2_huffman_skip(hs);
                }

                if (code1 < 0 || code2 < 0 || code3 < 0 || code4 < 0 || code5 < 0 || code6 < 0) {
                    jbig2_image_release(ctx, IB);
                    code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode data");
                    goto cleanup2;
                }
                if (code1 > 0 || code2 > 0 || code3 > 0 || code4 > 0 || code5 > 0 || code6 > 0) {
                    code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "OOB obtained when decoding symbol instance refinement data");
                    goto cleanup2;
                }

                /* 6.4.11 (6) */
                if (IB) {
                    IBO = IB;
                    IB = NULL;
                    if (((int32_t) IBO->width) + RDW < 0 || ((int32_t) IBO->height) + RDH < 0) {
                        code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "reference image dimensions negative");
                        goto cleanup2;
                    }
                    refimage = jbig2_image_new(ctx, IBO->width + RDW, IBO->height + RDH);
                    if (refimage == NULL) {
                        code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate reference image");
                        goto cleanup2;
                    }
                    jbig2_image_clear(ctx, refimage, 0x00);

                    /* Table 12 */
                    rparams.GRTEMPLATE = params->SBRTEMPLATE;
                    rparams.GRREFERENCE = IBO;
                    rparams.GRREFERENCEDX = (RDW >> 1) + RDX;
                    rparams.GRREFERENCEDY = (RDH >> 1) + RDY;
                    rparams.TPGRON = 0;
                    memcpy(rparams.grat, params->sbrat, 4);
                    code = jbig2_decode_refinement_region(ctx, segment, &rparams, as, refimage, GR_stats);
                    if (code < 0) {
                        jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode refinement region");
                        goto cleanup2;
                    }

                    jbig2_image_release(ctx, IBO);
                    IBO = NULL;
                    IB = refimage;
                    refimage = NULL;
                }

                /* 6.4.11 (7) */
                if (params->SBHUFF) {
                    code = jbig2_huffman_advance(hs, BMSIZE);
                    if (code < 0) {
                        jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to advance after huffman decoding refinement region");
                        goto cleanup2;
                    }
                }
            }

            /* (3c.vi) */
            if ((!params->TRANSPOSED) && (params->REFCORNER > 1) && IB) {
                CURS += IB->width - 1;
            } else if ((params->TRANSPOSED) && !(params->REFCORNER & 1) && IB) {
                CURS += IB->height - 1;
            }

            /* (3c.vii) */
            S = CURS;

            /* (3c.viii) */
            if (!params->TRANSPOSED) {
                switch (params->REFCORNER) {
                case JBIG2_CORNER_TOPLEFT:
                    x = S;
                    y = T;
                    break;
                case JBIG2_CORNER_TOPRIGHT:
                    if (IB)
                        x = S - IB->width + 1;
                    else
                        x = S + 1;
                    y = T;
                    break;
                case JBIG2_CORNER_BOTTOMLEFT:
                    x = S;
                    if (IB)
                        y = T - IB->height + 1;
                    else
                        y = T + 1;
                    break;
                default:
                case JBIG2_CORNER_BOTTOMRIGHT:
                    if (IB ) {
                        x = S - IB->width + 1;
                        y = T - IB->height + 1;
                    } else {
                        x = S + 1;
                        y = T + 1;
                    }
                    break;
                }
            } else {            /* TRANSPOSED */
                switch (params->REFCORNER) {
                case JBIG2_CORNER_TOPLEFT:
                    x = T;
                    y = S;
                    break;
                case JBIG2_CORNER_TOPRIGHT:
                    if (IB)
                        x = T - IB->width + 1;
                    else
                        x = T + 1;
                    y = S;
                    break;
                case JBIG2_CORNER_BOTTOMLEFT:
                    x = T;
                    if (IB)
                        y = S - IB->height + 1;
                    else
                        y = S + 1;
                    break;
                default:
                case JBIG2_CORNER_BOTTOMRIGHT:
                    if (IB) {
                        x = T - IB->width + 1;
                        y = S - IB->height + 1;
                    } else {
                        x = T + 1;
                        y = S + 1;
                    }
                    break;
                }
            }

            /* (3c.ix) */
#ifdef JBIG2_DEBUG
            jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number,
                        "composing glyph ID %d: %dx%d @ (%d,%d) symbol %d/%d", ID, IB->width, IB->height, x, y, NINSTANCES + 1, params->SBNUMINSTANCES);
#endif
            code = jbig2_image_compose(ctx, image, IB, x, y, params->SBCOMBOP);
            if (code < 0) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to compose symbol instance symbol bitmap into picture");
                goto cleanup2;
            }

            /* (3c.x) */
            if (IB && (!params->TRANSPOSED) && (params->REFCORNER < 2)) {
                CURS += IB->width - 1;
            } else if (IB && (params->TRANSPOSED) && (params->REFCORNER & 1)) {
                CURS += IB->height - 1;
            }

            /* (3c.xi) */
            NINSTANCES++;

            jbig2_image_release(ctx, IB);
            IB = NULL;
        }
        /* end strip */
    }
    /* 6.4.5 (4) */

cleanup2:
    jbig2_image_release(ctx, refimage);
    jbig2_image_release(ctx, IBO);
    jbig2_image_release(ctx, IB);
    if (params->SBHUFF) {
        jbig2_release_huffman_table(ctx, SBSYMCODES);
    }
    jbig2_huffman_free(ctx, hs);

    return code;
}

/**
 * jbig2_text_region: read a text region segment header
 **/
int
jbig2_text_region(Jbig2Ctx *ctx, Jbig2Segment *segment, const byte *segment_data)
{
    uint32_t offset = 0;
    Jbig2RegionSegmentInfo region_info;
    Jbig2TextRegionParams params;
    Jbig2Image *image = NULL;
    Jbig2SymbolDict **dicts = NULL;
    uint32_t n_dicts = 0;
    uint16_t flags = 0;
    uint16_t huffman_flags = 0;
    Jbig2ArithCx *GR_stats = NULL;
    int code = 0;
    Jbig2WordStream *ws = NULL;
    Jbig2ArithState *as = NULL;
    uint32_t table_index = 0;
    const Jbig2HuffmanParams *huffman_params = NULL;

    /* 7.4.1 */
    if (segment->data_length < 17)
        goto too_short;
    jbig2_get_region_segment_info(&region_info, segment_data);
    offset += 17;
    /* Check for T.88 amendment 3 */
    if (region_info.flags & 8)
        return jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "region segment flags indicate use of colored bitmap (NYI)");

    /* 7.4.3.1.1 */
    if (segment->data_length - offset < 2)
        goto too_short;
    flags = jbig2_get_uint16(segment_data + offset);
    offset += 2;

    jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "text region header flags 0x%04x", flags);

    /* zero params to ease cleanup later */
    memset(&params, 0, sizeof(Jbig2TextRegionParams));

    params.SBHUFF = flags & 0x0001;
    params.SBREFINE = flags & 0x0002;
    params.LOGSBSTRIPS = (flags & 0x000c) >> 2;
    params.SBSTRIPS = 1 << params.LOGSBSTRIPS;
    params.REFCORNER = (Jbig2RefCorner)((flags & 0x0030) >> 4);
    params.TRANSPOSED = flags & 0x0040;
    params.SBCOMBOP = (Jbig2ComposeOp)((flags & 0x0180) >> 7);
    params.SBDEFPIXEL = flags & 0x0200;
    /* SBDSOFFSET is a signed 5 bit integer */
    params.SBDSOFFSET = (flags & 0x7C00) >> 10;
    if (params.SBDSOFFSET > 0x0f)
        params.SBDSOFFSET -= 0x20;
    params.SBRTEMPLATE = flags & 0x8000;

    if (params.SBDSOFFSET) {
        jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number, "text region has SBDSOFFSET %d", params.SBDSOFFSET);
    }

    if (params.SBHUFF) {        /* Huffman coding */
        /* 7.4.3.1.2 */
        if (segment->data_length - offset < 2)
            goto too_short;
        huffman_flags = jbig2_get_uint16(segment_data + offset);
        offset += 2;

        if (huffman_flags & 0x8000)
            jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "reserved bit 15 of text region huffman flags is not zero");
    } else {                    /* arithmetic coding */

        /* 7.4.3.1.3 */
        if (segment->data_length - offset < 4)
            goto too_short;
        if ((params.SBREFINE) && !(params.SBRTEMPLATE)) {
            params.sbrat[0] = segment_data[offset];
            params.sbrat[1] = segment_data[offset + 1];
            params.sbrat[2] = segment_data[offset + 2];
            params.sbrat[3] = segment_data[offset + 3];
            offset += 4;
        }
    }

    /* 7.4.3.1.4 */
    if (segment->data_length - offset < 4)
        goto too_short;
    params.SBNUMINSTANCES = jbig2_get_uint32(segment_data + offset);
    offset += 4;

    if (params.SBHUFF) {
        /* 7.4.3.1.5 - Symbol ID Huffman table */
        /* ...this is handled in the segment body decoder */

        /* 7.4.3.1.6 - Other Huffman table selection */
        switch (huffman_flags & 0x0003) {
        case 0:                /* Table B.6 */
            params.SBHUFFFS = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_F);
            break;
        case 1:                /* Table B.7 */
            params.SBHUFFFS = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_G);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom FS huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFFS = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        case 2:                /* invalid */
        default:
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "text region specified invalid FS huffman table");
            goto cleanup1;
            break;
        }
        if (params.SBHUFFFS == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified FS huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x000c) >> 2) {
        case 0:                /* Table B.8 */
            params.SBHUFFDS = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_H);
            break;
        case 1:                /* Table B.9 */
            params.SBHUFFDS = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_I);
            break;
        case 2:                /* Table B.10 */
            params.SBHUFFDS = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_J);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom DS huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFDS = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        }
        if (params.SBHUFFDS == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified DS huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x0030) >> 4) {
        case 0:                /* Table B.11 */
            params.SBHUFFDT = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_K);
            break;
        case 1:                /* Table B.12 */
            params.SBHUFFDT = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_L);
            break;
        case 2:                /* Table B.13 */
            params.SBHUFFDT = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_M);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom DT huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFDT = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        }
        if (params.SBHUFFDT == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified DT huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x00c0) >> 6) {
        case 0:                /* Table B.14 */
            params.SBHUFFRDW = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_N);
            break;
        case 1:                /* Table B.15 */
            params.SBHUFFRDW = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_O);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom RDW huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFRDW = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        case 2:                /* invalid */
        default:
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "text region specified invalid RDW huffman table");
            goto cleanup1;
            break;
        }
        if (params.SBHUFFRDW == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified RDW huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x0300) >> 8) {
        case 0:                /* Table B.14 */
            params.SBHUFFRDH = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_N);
            break;
        case 1:                /* Table B.15 */
            params.SBHUFFRDH = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_O);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom RDH huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFRDH = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        case 2:                /* invalid */
        default:
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "text region specified invalid RDH huffman table");
            goto cleanup1;
            break;
        }
        if (params.SBHUFFRDH == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified RDH huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x0c00) >> 10) {
        case 0:                /* Table B.14 */
            params.SBHUFFRDX = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_N);
            break;
        case 1:                /* Table B.15 */
            params.SBHUFFRDX = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_O);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom RDX huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFRDX = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        case 2:                /* invalid */
        default:
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "text region specified invalid RDX huffman table");
            goto cleanup1;
            break;
        }
        if (params.SBHUFFRDX == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified RDX huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x3000) >> 12) {
        case 0:                /* Table B.14 */
            params.SBHUFFRDY = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_N);
            break;
        case 1:                /* Table B.15 */
            params.SBHUFFRDY = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_O);
            break;
        case 3:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom RDY huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFRDY = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        case 2:                /* invalid */
        default:
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "text region specified invalid RDY huffman table");
            goto cleanup1;
            break;
        }
        if (params.SBHUFFRDY == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified RDY huffman table");
            goto cleanup1;
        }

        switch ((huffman_flags & 0x4000) >> 14) {
        case 0:                /* Table B.1 */
            params.SBHUFFRSIZE = jbig2_build_huffman_table(ctx, &jbig2_huffman_params_A);
            break;
        case 1:                /* Custom table from referred segment */
            huffman_params = jbig2_find_table(ctx, segment, table_index);
            if (huffman_params == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "custom RSIZE huffman table not found (%d)", table_index);
                goto cleanup1;
            }
            params.SBHUFFRSIZE = jbig2_build_huffman_table(ctx, huffman_params);
            ++table_index;
            break;
        }
        if (params.SBHUFFRSIZE == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region specified RSIZE huffman table");
            goto cleanup1;
        }

        if (huffman_flags & 0x8000) {
            jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "text region huffman flags bit 15 is set, contrary to spec");
        }

        /* 7.4.3.1.7 */
        /* For convenience this is done in the body decoder routine */
    }

    jbig2_error(ctx, JBIG2_SEVERITY_INFO, segment->number,
                "text region: %d x %d @ (%d,%d) %d symbols", region_info.width, region_info.height, region_info.x, region_info.y, params.SBNUMINSTANCES);

    /* 7.4.3.2 (2) - compose the list of symbol dictionaries */
    n_dicts = jbig2_sd_count_referred(ctx, segment);
    if (n_dicts == 0) {
        jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "text region refers to no symbol dictionaries");
    } else {
        dicts = jbig2_sd_list_referred(ctx, segment);
        if (dicts == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "unable to retrieve symbol dictionaries! previous parsing error?");
            goto cleanup1;
        } else {
            uint32_t index;

            if (dicts[0] == NULL) {
                code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "unable to find first referenced symbol dictionary");
                goto cleanup1;
            }
            for (index = 1; index < n_dicts; index++)
                if (dicts[index] == NULL) {
                    jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "unable to find all referenced symbol dictionaries");
                    n_dicts = index;
                }
        }
    }

    /* 7.4.3.2 (3) */
    {
        int stats_size = params.SBRTEMPLATE ? 1 << 10 : 1 << 13;

        GR_stats = jbig2_new(ctx, Jbig2ArithCx, stats_size);
        if (GR_stats == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "could not allocate arithmetic decoder state");
            goto cleanup1;
        }
        memset(GR_stats, 0, stats_size);
    }

    image = jbig2_image_new(ctx, region_info.width, region_info.height);
    if (image == NULL) {
        code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region image");
        goto cleanup2;
    }

    if (offset >= segment->data_length)
        goto too_short;
    ws = jbig2_word_stream_buf_new(ctx, segment_data + offset, segment->data_length - offset);
    if (ws == NULL) {
        code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate word stream when handling text region image");
        goto cleanup2;
    }

    as = jbig2_arith_new(ctx, ws);
    if (as == NULL) {
        code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate arithmetic coding context when handling text region image");
        goto cleanup2;
    }

    if (!params.SBHUFF) {
        uint32_t SBSYMCODELEN, index;
        uint32_t SBNUMSYMS = 0;

        for (index = 0; index < n_dicts; index++) {
            SBNUMSYMS += dicts[index]->n_symbols;
        }

        params.IADT = jbig2_arith_int_ctx_new(ctx);
        params.IAFS = jbig2_arith_int_ctx_new(ctx);
        params.IADS = jbig2_arith_int_ctx_new(ctx);
        params.IAIT = jbig2_arith_int_ctx_new(ctx);
        if (params.IADT == NULL || params.IAFS == NULL || params.IADS == NULL || params.IAIT == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region image data");
            goto cleanup3;
        }

        /* Table 31 */
        for (SBSYMCODELEN = 0; (1U << SBSYMCODELEN) < SBNUMSYMS; SBSYMCODELEN++) {
        }
        params.IAID = jbig2_arith_iaid_ctx_new(ctx, SBSYMCODELEN);
        params.IARI = jbig2_arith_int_ctx_new(ctx);
        params.IARDW = jbig2_arith_int_ctx_new(ctx);
        params.IARDH = jbig2_arith_int_ctx_new(ctx);
        params.IARDX = jbig2_arith_int_ctx_new(ctx);
        params.IARDY = jbig2_arith_int_ctx_new(ctx);
        if (params.IAID == NULL || params.IARI == NULL ||
            params.IARDW == NULL || params.IARDH == NULL || params.IARDX == NULL || params.IARDY == NULL) {
            code = jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to allocate text region image data");
            goto cleanup4;
        }
    }

    code = jbig2_decode_text_region(ctx, segment, &params,
                                    (const Jbig2SymbolDict * const *)dicts, n_dicts, image,
                                    segment_data + offset, segment->data_length - offset, GR_stats, as, ws);
    if (code < 0) {
        jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "failed to decode text region image data");
        goto cleanup4;
    }

    if ((segment->flags & 63) == 4) {
        /* we have an intermediate region here. save it for later */
        segment->result = jbig2_image_reference(ctx, image);
    } else {
        /* otherwise composite onto the page */
        jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, segment->number,
                    "composing %dx%d decoded text region onto page at (%d, %d)", region_info.width, region_info.height, region_info.x, region_info.y);
        code = jbig2_page_add_result(ctx, &ctx->pages[ctx->current_page], image, region_info.x, region_info.y, region_info.op);
        if (code < 0)
            jbig2_error(ctx, JBIG2_SEVERITY_WARNING, segment->number, "unable to add text region to page");
    }

cleanup4:
    if (!params.SBHUFF) {
        jbig2_arith_iaid_ctx_free(ctx, params.IAID);
        jbig2_arith_int_ctx_free(ctx, params.IARI);
        jbig2_arith_int_ctx_free(ctx, params.IARDW);
        jbig2_arith_int_ctx_free(ctx, params.IARDH);
        jbig2_arith_int_ctx_free(ctx, params.IARDX);
        jbig2_arith_int_ctx_free(ctx, params.IARDY);
    }

cleanup3:
    if (!params.SBHUFF) {
        jbig2_arith_int_ctx_free(ctx, params.IADT);
        jbig2_arith_int_ctx_free(ctx, params.IAFS);
        jbig2_arith_int_ctx_free(ctx, params.IADS);
        jbig2_arith_int_ctx_free(ctx, params.IAIT);
    }
    jbig2_free(ctx->allocator, as);
    jbig2_word_stream_buf_free(ctx, ws);

cleanup2:
    jbig2_free(ctx->allocator, GR_stats);
    jbig2_image_release(ctx, image);

cleanup1:
    if (params.SBHUFF) {
        jbig2_release_huffman_table(ctx, params.SBHUFFFS);
        jbig2_release_huffman_table(ctx, params.SBHUFFDS);
        jbig2_release_huffman_table(ctx, params.SBHUFFDT);
        jbig2_release_huffman_table(ctx, params.SBHUFFRDX);
        jbig2_release_huffman_table(ctx, params.SBHUFFRDY);
        jbig2_release_huffman_table(ctx, params.SBHUFFRDW);
        jbig2_release_huffman_table(ctx, params.SBHUFFRDH);
        jbig2_release_huffman_table(ctx, params.SBHUFFRSIZE);
    }
    jbig2_free(ctx->allocator, dicts);

    return code;

too_short:
    return jbig2_error(ctx, JBIG2_SEVERITY_FATAL, segment->number, "segment too short");
}