prefer (X ? 1 : -1) when converting from boolean (1,0) to int (1,-1)

[pspp] / lib / xmemcoll.h

#include <stddef.h>
int xmemcoll (char *, size_t, char *, size_t);
int xmemcoll0 (char const *, size_t, char const *, size_t);