--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/jbig2dec/jbig2_arith_iaid.c	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,115 @@
+/* Copyright (C) 2001-2023 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.,  39 Mesa Street, Suite 108A, San Francisco,
+   CA 94129, USA, for further information.
+*/
+
+/*
+    jbig2dec
+*/
+
+/* Annex A.3 */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+#include "os_types.h"
+
+#include <stddef.h>
+#include <string.h>             /* memset() */
+
+#ifdef VERBOSE
+#include <stdio.h>              /* for debug printing only */
+#endif
+
+#include "jbig2.h"
+#include "jbig2_priv.h"
+#include "jbig2_arith.h"
+#include "jbig2_arith_iaid.h"
+
+struct _Jbig2ArithIaidCtx {
+    uint8_t SBSYMCODELEN;
+    Jbig2ArithCx *IAIDx;
+};
+
+Jbig2ArithIaidCtx *
+jbig2_arith_iaid_ctx_new(Jbig2Ctx *ctx, uint8_t SBSYMCODELEN)
+{
+    Jbig2ArithIaidCtx *result;
+    size_t ctx_size;
+
+    if (sizeof(ctx_size) * 8 <= SBSYMCODELEN)
+    {
+        jbig2_error(ctx, JBIG2_SEVERITY_FATAL, JBIG2_UNKNOWN_SEGMENT_NUMBER, "requested IAID arithmetic coding state size too large");
+        return NULL;
+    }
+
+    ctx_size = (size_t) 1U << SBSYMCODELEN;
+
+    result = jbig2_new(ctx, Jbig2ArithIaidCtx, 1);
+    if (result == NULL) {
+        jbig2_error(ctx, JBIG2_SEVERITY_FATAL, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to allocate IAID arithmetic coding state");
+        return NULL;
+    }
+
+    result->SBSYMCODELEN = SBSYMCODELEN;
+    result->IAIDx = jbig2_new(ctx, Jbig2ArithCx, ctx_size);
+    if (result->IAIDx == NULL)
+    {
+        jbig2_free(ctx->allocator, result);
+        jbig2_error(ctx, JBIG2_SEVERITY_FATAL, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to allocate symbol ID in IAID arithmetic coding state");
+        return NULL;
+    }
+
+    memset(result->IAIDx, 0, ctx_size);
+    return result;
+}
+
+/* A.3 */
+/* Return value: -1 on error, 0 on normal value */
+int
+jbig2_arith_iaid_decode(Jbig2Ctx *ctx, Jbig2ArithIaidCtx *actx, Jbig2ArithState *as, int32_t *p_result)
+{
+    Jbig2ArithCx *IAIDx = actx->IAIDx;
+    uint8_t SBSYMCODELEN = actx->SBSYMCODELEN;
+    /* A.3 (1) */
+    int PREV = 1;
+    int D;
+    int i;
+
+    /* A.3 (2) */
+    for (i = 0; i < SBSYMCODELEN; i++) {
+        D = jbig2_arith_decode(ctx, as, &IAIDx[PREV]);
+        if (D < 0)
+            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, JBIG2_UNKNOWN_SEGMENT_NUMBER, "failed to decode IAIDx code");
+#ifdef VERBOSE
+        fprintf(stderr, "IAID%x: D = %d\n", PREV, D);
+#endif
+        PREV = (PREV << 1) | D;
+    }
+    /* A.3 (3) */
+    PREV -= 1 << SBSYMCODELEN;
+#ifdef VERBOSE
+    fprintf(stderr, "IAID result: %d\n", PREV);
+#endif
+    *p_result = PREV;
+    return 0;
+}
+
+void
+jbig2_arith_iaid_ctx_free(Jbig2Ctx *ctx, Jbig2ArithIaidCtx *iax)
+{
+    if (iax != NULL) {
+        jbig2_free(ctx->allocator, iax->IAIDx);
+        jbig2_free(ctx->allocator, iax);
+    }
+}