tests: add REQUIRE_MEMEQ() macro

Actually prints out the offending memory regions. Very useful for
debugging, to avoid having to attach a (gdb) instance and poke at memory
regions every single time.

src/tests/tests.h

@@ -105,6 +105,45 @@ static inline bool feq(float a, float b, float epsilon)
     }                                                                           \
 } while (0)
 
+static inline void log_array(const uint8_t *a, const uint8_t *ref, size_t size)
+{
+    for (size_t n = 0; n < size; n++) {
+        const char *prefix = "", *suffix = "";
+        char terminator = ' ';
+        if (a[n] != ref[n]) {
+            prefix = "\033[31;1m";
+            suffix = "\033[0m";
+        }
+        if (n+1 == size || n % 16 == 15)
+            terminator = '\n';
+        fprintf(stderr, "%s%02"PRIx8"%s%c", prefix, a[n], suffix, terminator);
+    }
+}
+
+static inline void require_memeq(const void *aptr, const void *bptr, size_t size,
+                                 const char *astr, const char *bstr,
+                                 const char *sizestr, const char *file, int line)
+{
+    const uint8_t *a = aptr, *b = bptr;
+    for (size_t i = 0; i < size; i++) {
+        if (a[i] == b[i])
+            continue;
+
+        fprintf(stderr, "=== FAILED: memcmp(%s, %s, %s) == 0 at %s:%d\n"
+                        "at position %zu: 0x%02"PRIx8" != 0x%02"PRIx8"\n\n",
+                astr, bstr, sizestr, file, line, i, a[i], b[i]);
+
+        const size_t logsize = PL_MIN(size, PL_MAX(i+2, 512));
+        fprintf(stderr, "first %zu bytes of '%s':\n", logsize, astr);
+        log_array(a, b, logsize);
+        fprintf(stderr, "\nfirst %zu bytes of '%s':\n", logsize, bstr);
+        log_array(b, a, logsize);
+        exit(1);
+    }
+}
+
+#define REQUIRE_MEMEQ(a, b, size) require_memeq(a, b, size, #a, #b, #size, __FILE__, __LINE__)
+
 #define REQUIRE_HANDLE(shmem, type)                                             \
     switch (type) {                                                             \
     case PL_HANDLE_FD:                                                          \