feat(string): complete string.h + strdup/memccpy

src/string/strcat.c

@@ -0,0 +1,65 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <string.h>
+
+/*
+ * Append src (including its terminating NUL) to the end of dst; return dst.
+ * The strings must not overlap (restrict).
+ *
+ * See strcpy.c: the copy loop is a recognizable pattern, so disable
+ * -ftree-loop-distribute-patterns here too.
+ */
+__attribute__((optimize("no-tree-loop-distribute-patterns"))) char *
+strcat(char *restrict dst, const char *restrict src) // NOLINT(bugprone-*)
+{
+    char *d = dst;
+
+    /* Find the terminating NUL of dst. */
+    while (*d != '\0')
+    {
+        d++;
+    }
+
+    /* Append src including its NUL. */
+    for (;;)
+    {
+        *d++ = *src;
+        if (*src == '\0')
+        {
+            return dst;
+        }
+        src++;
+    }
+}
+
+/*
+ * Append at most n bytes of src to dst and always NUL-terminate; return dst.
+ *
+ * See strcpy.c: the copy loop is a recognizable pattern, so disable
+ * -ftree-loop-distribute-patterns here too.
+ */
+__attribute__((optimize("no-tree-loop-distribute-patterns"))) char *
+strncat(char *restrict dst, const char *restrict src, size_t n) // NOLINT(bugprone-*)
+{
+    char *d = dst;
+
+    /* Find the terminating NUL of dst. */
+    while (*d != '\0')
+    {
+        d++;
+    }
+
+    /* Append at most n bytes of src, stopping early at its NUL. */
+    while (n != 0 && *src != '\0')
+    {
+        *d++ = *src++;
+        n--;
+    }
+
+    /* strncat always NUL-terminates. */
+    *d = '\0';
+
+    return dst;
+}