+/**
+ * Decodes a base64 string into the original binary data it represents.
+ *
+ * Decodes the base64 string provided into binary, storing the result in the
+ * output buffer provided. The output buffer must be pre-allocated with enough
+ * space to store the result. The size needed can be found by calling the
+ * \ref base64_decode_size() function.
+ *
+ * If the output buffer is too small (based on the size provided) then the
+ * binary output may be only partially written.
+ *
+ * @param input The base64 string to encode. This doesn't need to be zero
+ * terminated.
+ * @param input_size The size of the input buffer to be converted.
+ * @param output A pre-allocated buffer to store the result.
+ * @param output_size The size of the allocated buffer, which will be updated
+ * to the number of bytes written to the buffer.
+ */