Given an array b[] of length n, pointers to &b[0]..&b[n] are defined
(where only &b[0]..&b[n-1] can be validly dereferenced). &b[-1], or
equivalently b-1, is not something we can use in valid Standard C.
gcc 6 diagnoses this as:
code/client/snd_wavelet.c:33:9: warning: array subscript is below array bounds [-Warray-bounds]
and might take this undefined behaviour as permission to emit
"more efficient" object code that is not what the author expected,
for example nothing at all. Use a macro to fake a 1-based array instead.
Simon McVittie
c5b6bb0d4b