release: restore ZUPT and harden source-only 5.2.2

tests/fixture_hex_decode.c

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later */
+#include <ctype.h>
+#include <stdio.h>
+
+static int hex_value(int character) {
+    if (character >= '0' && character <= '9') return character - '0';
+    if (character >= 'a' && character <= 'f') return character - 'a' + 10;
+    if (character >= 'A' && character <= 'F') return character - 'A' + 10;
+    return -1;
+}
+
+int main(int argc, char **argv) {
+    if (argc != 3) return 2;
+    FILE *input = fopen(argv[1], "rb");
+    FILE *output = input ? fopen(argv[2], "wb") : NULL;
+    if (!input || !output) {
+        if (input) fclose(input);
+        if (output) fclose(output);
+        return 1;
+    }
+    int high_nibble = -1;
+    int character;
+    int failed = 0;
+    while ((character = fgetc(input)) != EOF) {
+        if (isspace((unsigned char)character)) continue;
+        int value = hex_value(character);
+        if (value < 0) {
+            failed = 1;
+            break;
+        }
+        if (high_nibble < 0) {
+            high_nibble = value;
+        } else {
+            if (fputc((high_nibble << 4) | value, output) == EOF) {
+                failed = 1;
+                break;
+            }
+            high_nibble = -1;
+        }
+    }
+    if (ferror(input) || high_nibble >= 0 || fflush(output) != 0)
+        failed = 1;
+    if (fclose(input) != 0) failed = 1;
+    if (fclose(output) != 0) failed = 1;
+    return failed ? 1 : 0;
+}