undefined behaviour in hamt.c

[Bruno Haible]

Hi Marc,

When running the gnulib tests with clang's UndefinedBehaviorSanitizer, I got
this output in test-hamt.log:

../../gllib/hamt.c:685:41: runtime error: shift exponent 65 is too large for 
64-bit type 'size_t' (aka 'unsigned long')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior 
../../gllib/hamt.c:685:41 in 
PASS test-hamt (exit status: 0)

How to reproduce:
1. Install clang 13.
2. Set CC, CXX, CFLAGS, CXXFLAGS:
   CC="clang 
-fsanitize=undefined,signed-integer-overflow,shift,integer-divide-by-zero 
-fno-sanitize=pointer-overflow"; \
   CXX="clang++ -L/usr/lib/gcc/x86_64-linux-gnu/9 -I/usr/include/c++/9 
-I/usr/include/x86_64-linux-gnu/c++/9 
-fsanitize=undefined,signed-integer-overflow,shift,integer-divide-by-zero 
-fno-sanitize=pointer-overflow"; \
   CFLAGS="-O1 -fno-omit-frame-pointer -ggdb"; \
   CXXFLAGS="-O1 -fno-omit-frame-pointer -ggdb"; \
   export CC CXX CFLAGS CXXFLAGS
   (The set of -I options in CXX depend on your local g++ installation.)
3. Prepare a gnulib testdir.
4. Configure, make, make check
5. Search the *.log files for 'UndefinedBehaviorSanitizer'.

Bruno