Add .gitignore.
Do not optimize coverage builds.
Cleanup Makefile.
Add missing closing brace.
Fix whitespace at the end of the line.
Add #define to support mkdtemp in stdlib.h on GCC 4.6.3.
Use sizeof(*ptr) rather than sizeof(type).
Add SSE/AVX code paths to perform xor.
Clang doesn't understand -floop-optimize; -O3 probably achieves a similar result.