/* Copyright (C) 2001-2020 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
*/

/* Annex A */

#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"

struct _Jbig2ArithIntCtx {
    Jbig2ArithCx IAx[512];
};

Jbig2ArithIntCtx *
jbig2_arith_int_ctx_new(Jbig2Ctx *ctx)
{
    Jbig2ArithIntCtx *result = jbig2_new(ctx, Jbig2ArithIntCtx, 1);

    if (result == NULL) {
        jbig2_error(ctx, JBIG2_SEVERITY_FATAL, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to allocate arithmetic integer coding state");
        return NULL;
    } else {
        memset(result->IAx, 0, sizeof(result->IAx));
    }

    return result;
}

/* A.2 */
/* Return value: -1 on error, 0 on normal value, 1 on OOB return. */
int
jbig2_arith_int_decode(Jbig2Ctx *ctx, Jbig2ArithIntCtx *actx, Jbig2ArithState *as, int32_t *p_result)
{
    Jbig2ArithCx *IAx = actx->IAx;
    int PREV = 1;
    int S;
    int32_t V;
    int bit;
    int n_tail, offset;
    int i;

    S = jbig2_arith_decode(ctx, as, &IAx[PREV]);
    if (S < 0)
        return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx S");
    PREV = (PREV << 1) | S;

    bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
    if (bit < 0)
        return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx decision bit 0");
    PREV = (PREV << 1) | bit;
    if (bit) {
        bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
        if (bit < 0)
            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx decision bit 1");
        PREV = (PREV << 1) | bit;

        if (bit) {
            bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
            if (bit < 0)
                return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx decision bit 2");
            PREV = (PREV << 1) | bit;

            if (bit) {
                bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
                if (bit < 0)
                    return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx decision bit 3");
                PREV = (PREV << 1) | bit;

                if (bit) {
                    bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
                    if (bit < 0)
                        return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx decision bit 4");
                    PREV = (PREV << 1) | bit;

                    if (bit) {
                        n_tail = 32;
                        offset = 4436;
                    } else {
                        n_tail = 12;
                        offset = 340;
                    }
                } else {
                    n_tail = 8;
                    offset = 84;
                }
            } else {
                n_tail = 6;
                offset = 20;
            }
        } else {
            n_tail = 4;
            offset = 4;
        }
    } else {
        n_tail = 2;
        offset = 0;
    }

    V = 0;
    for (i = 0; i < n_tail; i++) {
        bit = jbig2_arith_decode(ctx, as, &IAx[PREV]);
        if (bit < 0)
            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAx V bit %d", i);
        PREV = ((PREV << 1) & 511) | (PREV & 256) | bit;
        V = (V << 1) | bit;
    }

    /* offset is always >=0, so underflow can't happen. */
    /* avoid overflow by clamping 32 bit value. */
    if (V > INT32_MAX - offset)
        V = INT32_MAX;
    else
        V += offset;
    V = S ? -V : V;
    *p_result = V;
    return S && V == 0 ? 1 : 0;
}

void
jbig2_arith_int_ctx_free(Jbig2Ctx *ctx, Jbig2ArithIntCtx *iax)
{
    jbig2_free(ctx->allocator, iax);
}
