Math macros

        #define sqr(x)      ((x) * (x))
        #define isgn(x)     ((x) < 0 ? -1 : 1)
        #define lsgn(x)     ((x) < 0l ? -1 : 1)
        #define fsgn(x)     ((x) < 0.0 ? -1 : 1)
        #define sign(x)     isgn(x)
        #define sgn(x)      isgn(x)
        #define lsign(x)    lsgn(x)
        #define fsign(x)    fsgn(x)
        #define swap(x,y)   (x=y, y=x, x=y)
        #define mid(a,x,b)  ((((a) <= (x)) && ((x) <= (b))) ? 1 : 0)