From: Rudolf Polzer <divverent@xonotic.org>
Date: Fri, 11 Oct 2013 04:33:13 +0000 (+0200)
Subject: use a proper binary search
X-Git-Tag: xonotic-v0.8.0~256^2~23
X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=8cedf0c162fcfe347d2f7dccaf33053210c870ca;p=xonotic%2Fxonotic-data.pk3dir.git

use a proper binary search
---

diff --git a/qcsrc/menu/xonotic/serverlist.c b/qcsrc/menu/xonotic/serverlist.c
index 216a98adb..a69f310cc 100644
--- a/qcsrc/menu/xonotic/serverlist.c
+++ b/qcsrc/menu/xonotic/serverlist.c
@@ -670,124 +670,75 @@ void XonoticServerList_draw(entity me)
 		// ^ unfortunately no such optimization can be made-- we must process through the
 		// entire list, otherwise there is no way to know which item is first in its category.
 
-		if(itemcount)
-		{
-			// binary search method suggested by div
-			/*float cat = 0, x;
-			float first, middle, last;
-			float newfirst = 0;
-			float catf = 0, catl = 0;
-			for(x = 1; x <= category_ent_count; ++x)
-			{
-				first = newfirst;
-				last = (itemcount - 1);
-				middle = floor((first + last) / 2);
-
-				if(
-					((catf = gethostcachenumber(SLIST_FIELD_CATEGORY, first)) < x)
-					&&
-					((catl = gethostcachenumber(SLIST_FIELD_CATEGORY, last)) >= x)
-				)
-				{
-					for(;;)
-					{
-						cat = gethostcachenumber(SLIST_FIELD_CATEGORY, middle);
-						if(cat >= x) { last = middle; }
-						else if(cat < x) { first = middle; }
-						if((last - middle) == 1)
-						{
-							print(sprintf("highhit: x='%d', dc='%d', first='%d', middle='%d', last='%d', cat='%d'.\n", x, category_draw_count, first, middle, last, cat));
-							category_name[category_draw_count] = x;
-							category_item[category_draw_count] = last;
-							++category_draw_count;
-							++me.nItems;
-							newfirst = last; // already scanned through these, skip 'em
-							break;
-						}
-						middle = floor((first + last) / 2);
+		// binary search method suggested by div
+		float x;
+		float begin = 0;
+		for(x = 1; x <= category_ent_count; ++x) {
+			float first = begin;
+			float last = (itemcount - 1);
+			if (first > last) {
+				// List is empty.
+				break;
+			}
+			float catf = gethostcachenumber(SLIST_FIELD_CATEGORY, first);
+			float catl = gethostcachenumber(SLIST_FIELD_CATEGORY, last);
+			if (catf > x) {
+				// The first one is already > x.
+				// Therefore, category x does not exist.
+				// Higher numbered categories do exist though.
+			} else if (catl < x) {
+				// The last one is < x.
+				// Thus this category - and any following -
+				// don't exist.
+				break;
+			} else if (catf == x) {
+				// Starts at first. This breaks the loop
+				// invariant in the binary search and thus has
+				// to be handled separately.
+				print(sprintf("hit: x='%d', dc='%d', first='%d', last='%d', catf='%d', catl='%d'.\n", x, category_draw_count, first, last, catf, catl));
+				category_name[category_draw_count] = x;
+				category_item[category_draw_count] = first;
+				++category_draw_count;
+				++me.nItems;
+				begin = first + 1;
+			} else {
+				// At this point, catf <= x < catl, thus
+				// catf < catl, thus first < last.
+				// INVARIANTS:
+				// last - first >= 1
+				// catf == gethostcachenumber(SLIST_FIELD_CATEGORY(first)
+				// catl == gethostcachenumber(SLIST_FIELD_CATEGORY(last)
+				// catf < x
+				// catl >= x
+				while (last - first > 1) {
+					float middle = floor((first + last) / 2);
+					// By loop condition, middle != first && middle != last.
+					float cat = gethostcachenumber(SLIST_FIELD_CATEGORY, middle);
+					if (cat >= x) {
+						last = middle;
+						catl = cat;
+					} else {
+						first = middle;
+						catf = cat;
 					}
 				}
-				else if(catf == x)
-				{
-					print(sprintf("lowhit: x='%d', dc='%d', first='%d', middle='%d', last='%d', cat='%d'.\n", x, category_draw_count, first, middle, last, catf));
+				if (catl == x) {
+					print(sprintf("hit: x='%d', dc='%d', first='%d', last='%d', catf='%d', catl='%d'.\n", x, category_draw_count, first, last, catf, catl));
 					category_name[category_draw_count] = x;
-					category_item[category_draw_count] = first;
+					category_item[category_draw_count] = last;
 					++category_draw_count;
 					++me.nItems;
-					newfirst = first + 1; // already scanned through these, skip 'em
-				}
-			}*/
-
-			// my binary search method
-			float cat = 0, x;
-			float first, middle, last;
-			float newfirst = 0;
-			for(x = 1; x <= category_ent_count; ++x)
-			{
-				first = newfirst;
-				last = (itemcount - 1);
-				middle = floor((first + last) / 2);
-
-				while(first <= last)
-				{
-					cat = gethostcachenumber(SLIST_FIELD_CATEGORY, middle);
-					if(cat > x) { last = middle - 1; }
-					else if(cat == x)
-					{
-						if(middle == 0 || (gethostcachenumber(SLIST_FIELD_CATEGORY, middle - 1) != x)) // check if middle is the first of its category
-						{
-							//print(sprintf("hit: x='%d', dc='%d', first='%d', middle='%d', last='%d', cat='%d'.\n", x, category_draw_count, first, middle, last, cat));
-							category_name[category_draw_count] = cat;
-							category_item[category_draw_count] = middle;
-							++category_draw_count;
-							++me.nItems;
-							newfirst = middle + 1; // already scanned through these, skip 'em
-							break;
-						}
-						else { last = middle - 1; } // nope, try again
-					}
-					else { first = middle + 1; }
-					middle = floor((first + last) / 2);
 				}
+				begin = last + 1; // already scanned through these, skip 'em
 			}
+		}
 
-			// old linear search method
-			/*float cat = 0, i = 0, x = 0; 
-			for(i = 0; i < itemcount; ++i) // FIXME this loop is TOTALLY unacceptable (O(servers)). Make it O(categories * log(servers)). Yes, that is possible.
-			{
-				cat = gethostcachenumber(SLIST_FIELD_CATEGORY, i);
-				if(cat)
-				{
-					if(category_draw_count == 0)
-					{
-						print(sprintf("hit: i='%d', dc='%d', cat='%d'.\n", i, category_draw_count, cat));
-						category_name[category_draw_count] = cat;
-						category_item[category_draw_count] = i;
-						++category_draw_count;
-						++me.nItems;
-					}
-					else
-					{
-						found = 0;
-						for(x = 0; x < category_draw_count; ++x) { if(cat == category_name[x]) { found = 1; } }
-						if not(found)
-						{
-							print(sprintf("hit: i='%d', dc='%d', cat='%d'.\n", i, category_draw_count, cat));
-							category_name[category_draw_count] = cat;
-							category_item[category_draw_count] = i;
-							++category_draw_count;
-							++me.nItems;
-						}
-					}
-				}
-			}*/
-			if(autocvar_menu_slist_categories_onlyifmultiple && (category_draw_count == 1))
-			{
-				category_name[0] = -1;
-				category_item[0] = -1;
-				category_draw_count = 0;
-				me.nItems = itemcount;
-			}
+		if(autocvar_menu_slist_categories_onlyifmultiple && (category_draw_count == 1))
+		{
+			category_name[0] = -1;
+			category_item[0] = -1;
+			category_draw_count = 0;
+			me.nItems = itemcount;
 		}
 	}
 	else { me.nItems = gethostcachevalue(SLIST_HOSTCACHEVIEWCOUNT); }