--- /dev/null
+/*
+ * Copyright (c) 2017 Lev Walkin <vlm@lionet.info>.
+ * All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#include <asn_internal.h>
+#include <INTEGER.h>
+
+/*
+ * Encode INTEGER type using DER.
+ */
+asn_enc_rval_t
+INTEGER_encode_der(const asn_TYPE_descriptor_t *td, const void *sptr,
+ int tag_mode, ber_tlv_tag_t tag, asn_app_consume_bytes_f *cb,
+ void *app_key) {
+ const INTEGER_t *st = (const INTEGER_t *)sptr;
+ asn_enc_rval_t rval;
+ INTEGER_t effective_integer;
+
+ ASN_DEBUG("%s %s as INTEGER (tm=%d)",
+ cb?"Encoding":"Estimating", td->name, tag_mode);
+
+ /*
+ * Canonicalize integer in the buffer.
+ * (Remove too long sign extension, remove some first 0x00 bytes)
+ */
+ if(st->buf) {
+ uint8_t *buf = st->buf;
+ uint8_t *end1 = buf + st->size - 1;
+ int shift;
+
+ /* Compute the number of superfluous leading bytes */
+ for(; buf < end1; buf++) {
+ /*
+ * If the contents octets of an integer value encoding
+ * consist of more than one octet, then the bits of the
+ * first octet and bit 8 of the second octet:
+ * a) shall not all be ones; and
+ * b) shall not all be zero.
+ */
+ switch(*buf) {
+ case 0x00:
+ if((buf[1] & 0x80) == 0) continue;
+ break;
+ case 0xff:
+ if((buf[1] & 0x80)) continue;
+ break;
+ }
+ break;
+ }
+
+ /* Remove leading superfluous bytes from the integer */
+ shift = buf - st->buf;
+ if(shift) {
+ union {
+ const uint8_t *c_buf;
+ uint8_t *nc_buf;
+ } unconst;
+ unconst.c_buf = st->buf;
+ effective_integer.buf = unconst.nc_buf + shift;
+ effective_integer.size = st->size - shift;
+
+ st = &effective_integer;
+ }
+ }
+
+ rval = der_encode_primitive(td, st, tag_mode, tag, cb, app_key);
+ if(rval.structure_ptr == &effective_integer) {
+ rval.structure_ptr = sptr;
+ }
+ return rval;
+}