UBSAN: index -1 out of bounds for type float [512] in lib_com/ifft_rel.c

Undefined behaviour sanitizer complains about ifft_rel.c:232:

    xi0 = temp - 1;

lib_com/ifft_rel.c:232:16: runtime error: index -1 out of bounds for type 'float [512]'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior lib_com/ifft_rel.c:232:16 in 

This is not a bug, though, as xi0 is either overwritten or indexed in starting with 1. To silence the warning, this line can be rewritten like so:

    xi0 = &temp[0] - 1;

Alternatively, one can add it to the ignorelist for the sanitizer test, but fixing it is probably the same amount of effort.