Re: [PATCH] base64: provide a fast path for encoding well sized buffers

[Paul Eggert]

Pádraig Brady wrote:
> +  static const char b64c[64] =
> +    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
...
> +  static const char b64c[64] =
>      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

There only needs to be one copy of b64c.

> +  if ((inlen % 3 == 0) && BASE64_LENGTH (inlen) == outlen)

This divides by 3 twice, once for % and once for BASE64_LENGTH,
and if we want to be truly paranoid it can mess up due to overflow,
e.g., on a 32-bit host if inlen == 2**32 - 1 && outlen == 0.

How about this instead?

  if (outlen % 4 == 0 && inlen == outlen / 4 * 3)

where any decent compiler should do the right thing and
generate only shifts, masks, and adds; and there's no
problem with overflow.