Re: Coverity false positives triggered by gnulib's implementation of base64

[Bruno Haible <bruno@clisp.org>]

Kamil Dudka wrote:
> Thanks!  This also helps to suppress the false positives on cryptsetup
> with Coverity Static Analysis version 2019.03.

Good! Since this is the approach that Paul prefers, I'm pushing this one:


2019-05-10  Bruno Haible  <bruno@clisp.org>

	base64: Avoid false positive warning from Coverity.
	Reported by Kamil Dudka <kdudka@redhat.com>.
	Idea by Paul Eggert.
	* lib/base64.c (base64_encode_fast, base64_encode): Add a no-op
	'& 0x3f' to the array index expressions. This convinces Coverity that
	there is no out-of-bounds array reference, regardless of the input.

diff --git a/lib/base64.c b/lib/base64.c
index f3f7298..a00e0f4 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -70,7 +70,7 @@ base64_encode_fast (const char *restrict in, size_t inlen, char *restrict out)
 {
   while (inlen)
     {
-      *out++ = b64c[to_uchar (in[0]) >> 2];
+      *out++ = b64c[(to_uchar (in[0]) >> 2) & 0x3f];
       *out++ = b64c[((to_uchar (in[0]) << 4) + (to_uchar (in[1]) >> 4)) & 0x3f];
       *out++ = b64c[((to_uchar (in[1]) << 2) + (to_uchar (in[2]) >> 6)) & 0x3f];
       *out++ = b64c[to_uchar (in[2]) & 0x3f];
@@ -103,7 +103,7 @@ base64_encode (const char *restrict in, size_t inlen,
 
   while (inlen && outlen)
     {
-      *out++ = b64c[to_uchar (in[0]) >> 2];
+      *out++ = b64c[(to_uchar (in[0]) >> 2) & 0x3f];
       if (!--outlen)
         break;
       *out++ = b64c[((to_uchar (in[0]) << 4)