Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/asn1/support/aper_encoder.c

@@ -0,0 +1,129 @@
+#include "asn_application.h"
+#include "asn_internal.h"
+#include "aper_encoder.h"
+
+/*
+ * Argument type and callback necessary for aper_encode_to_buffer().
+ */
+typedef struct enc_to_buf_arg {
+	void *buffer;
+	size_t left;
+} enc_to_buf_arg;
+static int encode_to_buffer_cb(const void *buffer, size_t size, void *key) {
+	enc_to_buf_arg *arg = (enc_to_buf_arg *)key;
+
+	if(arg->left < size)
+		return -1;	/* Data exceeds the available buffer size */
+
+	memcpy(arg->buffer, buffer, size);
+	arg->buffer = ((char *)arg->buffer) + size;
+	arg->left -= size;
+
+	return 0;
+}
+
+asn_enc_rval_t
+aper_encode_to_buffer(const asn_TYPE_descriptor_t *td,
+                      const asn_per_constraints_t *constraints,
+                      const void *sptr, void *buffer, size_t buffer_size) {
+    enc_to_buf_arg key;
+
+    key.buffer = buffer;
+    key.left = buffer_size;
+
+    if(td) ASN_DEBUG("Encoding \"%s\" using ALIGNED PER", td->name);
+
+    return aper_encode(td, constraints, sptr, encode_to_buffer_cb, &key);
+}
+
+ssize_t
+aper_encode_to_new_buffer(const asn_TYPE_descriptor_t *td,
+                          const asn_per_constraints_t *constraints,
+                          const void *sptr, void **buffer_r) {
+    asn_enc_rval_t er = {0,0,0};
+	enc_dyn_arg key;
+
+	memset(&key, 0, sizeof(key));
+
+	er = aper_encode(td, constraints, sptr, encode_dyn_cb, &key);
+	switch(er.encoded) {
+	case -1:
+		FREEMEM(key.buffer);
+		return -1;
+	case 0:
+		FREEMEM(key.buffer);
+		key.buffer = MALLOC(1);
+		if(key.buffer) {
+			*(char *)key.buffer = '\0';
+			*buffer_r = key.buffer;
+			return 1;
+		} else {
+			return -1;
+		}
+	default:
+		*buffer_r = key.buffer;
+		ASN_DEBUG("Complete encoded in %ld bits", (long)er.encoded);
+		return ((er.encoded + 7) >> 3);
+	}
+}
+
+/*
+ * Internally useful functions.
+ */
+
+/* Flush partially filled buffer */
+static int
+_aper_encode_flush_outp(asn_per_outp_t *po) {
+	uint8_t *buf;
+
+	if(po->nboff == 0 && po->buffer == po->tmpspace)
+		return 0;
+
+	buf = po->buffer + (po->nboff >> 3);
+	/* Make sure we account for the last, partially filled */
+	if(po->nboff & 0x07) {
+		buf[0] &= 0xff << (8 - (po->nboff & 0x07));
+		buf++;
+	}
+
+	if (po->output) {
+		return po->output(po->tmpspace, buf - po->tmpspace, po->op_key);
+	}
+	return 0;
+}
+
+asn_enc_rval_t
+aper_encode(const asn_TYPE_descriptor_t *td,
+        const asn_per_constraints_t *constraints,
+        const void *sptr, asn_app_consume_bytes_f *cb, void *app_key) {
+	asn_per_outp_t po;
+	asn_enc_rval_t er = {0,0,0};
+
+	/*
+	 * Invoke type-specific encoder.
+	 */
+	if(!td || !td->op->aper_encoder)
+		ASN__ENCODE_FAILED;	 /* PER is not compiled in */
+
+	po.buffer = po.tmpspace;
+	po.nboff = 0;
+	po.nbits = 8 * sizeof(po.tmpspace);
+	po.output = cb ? cb : ignore_output;
+	po.op_key = app_key;
+	po.flushed_bytes = 0;
+
+	er = td->op->aper_encoder(td, constraints, sptr, &po);
+	if(er.encoded != -1) {
+		size_t bits_to_flush;
+
+		bits_to_flush = ((po.buffer - po.tmpspace) << 3) + po.nboff;
+
+		/* Set number of bits encoded to a firm value */
+		er.encoded = (po.flushed_bytes << 3) + bits_to_flush;
+
+		if(_aper_encode_flush_outp(&po))
+			ASN__ENCODE_FAILED;
+	}
+
+	return er;
+}