terminal.[ch]: refactor the 'pos' macros.

These are now inline functions (mostly, except for a couple of macro
wrappers to preserve the old call syntax), and they live in terminal.h
instead of at the top of terminal.c.

Also, I've added a few comments for clarity, and renamed the posPlt()
function, which didn't do at all what the name made it look (at least
to a mathematician familiar with product orders) as if it did.

terminal.c

@@ -13,22 +13,6 @@
 #include "putty.h"
 #include "terminal.h"
 
-#define poslt(p1,p2) ( (p1).y < (p2).y || ( (p1).y == (p2).y && (p1).x < (p2).x ) )
-#define posle(p1,p2) ( (p1).y < (p2).y || ( (p1).y == (p2).y && (p1).x <= (p2).x ) )
-#define poseq(p1,p2) ( (p1).y == (p2).y && (p1).x == (p2).x )
-#define posdiff(p1,p2) ( ((p1).y - (p2).y) * (term->cols+1) + (p1).x - (p2).x )
-
-/* Product-order comparisons for rectangular block selection. */
-#define posPlt(p1,p2) ( (p1).y <= (p2).y && (p1).x < (p2).x )
-#define posPle(p1,p2) ( (p1).y <= (p2).y && (p1).x <= (p2).x )
-
-#define incpos(p) ( (p).x == term->cols ?               \
-                    ((p).x = 0, (p).y++, true) :        \
-                    ((p).x++, false) )
-#define decpos(p) ( (p).x == 0 ?                                \
-                    ((p).x = term->cols, (p).y--, true) :       \
-                    ((p).x--, false) )
-
 #define VT52_PLUS
 
 #define CL_ANSIMIN	0x0001	       /* Codes in all ANSI like terminals. */
@@ -5492,7 +5476,7 @@ static void do_paint(Terminal *term)
 				poslt(scrpos, term->selend));
 		else
 		    selected = (posPle(term->selstart, scrpos) &&
-				posPlt(scrpos, term->selend));
+				posPle_left(scrpos, term->selend));
 	    } else
 		selected = false;
 	    tattr = (tattr ^ rv

terminal.h

@@ -385,4 +385,94 @@ static inline int term_char_width(Terminal *term, unsigned int c)
  */
 #define CC_LIMIT 32
 
+/* ----------------------------------------------------------------------
+ * Helper functions for dealing with the small 'pos' structure.
+ */
+
+static inline bool poslt(pos p1, pos p2)
+{
+    if (p1.y != p2.y)
+        return p1.y < p2.y;
+    return p1.x < p2.x;
+}
+
+static inline bool posle(pos p1, pos p2)
+{
+    if (p1.y != p2.y)
+        return p1.y < p2.y;
+    return p1.x <= p2.x;
+}
+
+static inline bool poseq(pos p1, pos p2)
+{
+    return p1.y == p2.y && p1.x == p2.x;
+}
+
+static inline int posdiff_fn(pos p1, pos p2, int cols)
+{
+    return (p1.y - p2.y) * (cols+1) + (p1.x - p2.x);
+}
+
+/* Convenience wrapper on posdiff_fn which uses the 'Terminal *term'
+ * that more or less every function in terminal.c will have in scope.
+ * For safety's sake I include a TYPECHECK that ensures it really is a
+ * structure pointer of the right type. */
+#define GET_TERM_COLS TYPECHECK(term == (Terminal *)0, term->cols)
+#define posdiff(p1,p2) posdiff_fn(p1, p2, GET_TERM_COLS)
+
+/* Product-order comparisons for rectangular block selection. */
+
+static inline bool posPle(pos p1, pos p2)
+{
+    return p1.y <= p2.y && p1.x <= p2.x;
+}
+
+static inline bool posPle_left(pos p1, pos p2)
+{
+    /*
+     * This function is used for checking whether a given character
+     * cell of the terminal ought to be highlighted as part of the
+     * selection, by comparing with term->selend. term->selend stores
+     * the location one space to the right of the last highlighted
+     * character. So we want to highlight the characters that are
+     * less-or-equal (in the product order) to the character just left
+     * of p2.
+     *
+     * (Setting up term->selend that way was the easiest way to get
+     * rectangular selection working at all, in a code base that had
+     * done lexicographic selection the way I happened to have done
+     * it.)
+     */
+    return p1.y <= p2.y && p1.x < p2.x;
+}
+
+static inline bool incpos_fn(pos *p, int cols)
+{
+    if (p->x == cols) {
+        p->x = 0;
+        p->y++;
+        return true;
+    }
+    p->x++;
+    return false;
+}
+
+static inline bool decpos_fn(pos *p, int cols)
+{
+    if (p->x == 0) {
+        p->x = cols;
+        p->y--;
+        return true;
+    }
+    p->x--;
+    return false;
+}
+
+/* Convenience wrappers on incpos and decpos which use term->cols
+ * (similarly to posdiff above), and also (for mild convenience and
+ * mostly historical inertia) let you leave off the & at every call
+ * site. */
+#define incpos(p) incpos_fn(&(p), GET_TERM_COLS)
+#define decpos(p) decpos_fn(&(p), GET_TERM_COLS)
+
 #endif