I recently added '-Wextra' to my compile flags and I get many of the following
warnings when compiling libgcrypt.

warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

I have looked through them all and most of them are comparing a signed counter
with size_t or unsigned int, which should be benign. However, researching the
warning there are certain nasty bugs that appear if the signed int is ever
negative...

http://www.jwwalker.com/pages/safe-compare.html

https://www.securecoding.cert.org/confluence/display/cplusplus/INT02-CPP.+Understand+integer+conversion+rules

I'm willing to help change the counters to unsigned int, like they should be.
However, some of the changes required are harder for me to understand how to fix.