worms.c: formatting of complicated conditionals

[Kragen Javier Sitaker]

// Diomidis Spinellis's book "Code Reading: An Open Source
// Perspective" has this messy code in chapter 2
// > http://www.spinellis.gr/codereading/spinellisch02.pdf
// from netbsdsrc/games/worms/worms.c:419:

op = &(!x ? (!y ? upleft : (y == bottom ? lowleft : left)) :
(x == last ? (!y ? upright : (y == bottom ? lowright : right)) :
(!y ? upper : (y == bottom ? lower : normal))))[w->orientation];

// He rewrites it as follows, the idea being to improve its
// readability:

struct options *locations[3][3] = {
     {upleft, upper, upright},
     {left,    normal, right},
     {lowleft, lower, lowright},
};
int xlocation, ylocation;
// Determine x offset
if (x == 0)
     xlocation = 0;
else if (x ==  last)
     xlocation = 2;
else
     xlocation = 1;
// Determine y offset
if (y == 0)
     ylocation = 0;
else if (y ==  bottom)
     ylocation = 2;
else
     ylocation = 1;
op = &(locations[ylocation][xlocation])[w->orientation];

// In my opinion, the above is actually worse than the original, as a
// result of being so much longer.  However, then Spinellis suggests
// this version, which he credits to Guy Steele:

op =
  &(        !y ? (!x ?  upleft : x!=last ?  upper :  upright ) :
     y!=bottom ? (!x ?    left : x!=last ? normal :    right ) :
                 (!x ? lowleft : x!=last ?  lower : lowright )
   )[w->orientation];


// I agree that the code needs rewriting, but inspired by Scheme, I
// would do it without magic numbers, without nine separate variables
// for the struct options pointers, and with conditions and their
// consequents on the same line:

struct bar { struct options *left, *middle, *right } upper, middle, lower;
struct bar *a = (y == 0      ? &upper :
                 y == bottom ? &lower :
                               &middle);
struct options *b = (x == 0    ? a->left  :
                     x == last ? a->right :
                                 a->middle);
op = &b[w->orientation];