--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/jbig2dec/jbig2_arith_int.c	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,148 @@
+/* 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 */
+
+#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);
+}