diff --git a/heightmap.lua b/heightmap.lua
index b41236c..cbe8923 100644
--- a/heightmap.lua
+++ b/heightmap.lua
@@ -8,6 +8,10 @@ local riverbed_slope = mapgen_rivers.settings.riverbed_slope * mapgen_rivers.set
 
 local MAP_BOTTOM = -31000
 
+-- Localize for performance
+local floor, min, max = math.floor, math.min, math.max
+local unpk = unpack
+
 -- Linear interpolation
 local function interp(v00, v01, v11, v10, xf, zf)
 	local v0 = v01*xf + v00*(1-xf)
@@ -30,11 +34,11 @@ local function heightmaps(minp, maxp)
 
 			if poly then
 				local xf, zf = transform_quadri(poly.x, poly.z, x, z)
-				local i00, i01, i11, i10 = unpack(poly.i)
+				local i00, i01, i11, i10 = unpk(poly.i)
 
 				-- Load river width on 4 edges and corners
-				local r_west, r_north, r_east, r_south = unpack(poly.rivers)
-				local c_NW, c_NE, c_SE, c_SW = unpack(poly.river_corners)
+				local r_west, r_north, r_east, r_south = unpk(poly.rivers)
+				local c_NW, c_NE, c_SE, c_SW = unpk(poly.river_corners)
 
 				-- Calculate the depth factor for each edge and corner.
 				-- Depth factor:
@@ -64,10 +68,10 @@ local function heightmaps(minp, maxp)
 
 				-- Transform the coordinates to have xf and zf = 0 or 1 in rivers (to avoid rivers having lateral slope and to accomodate the surrounding smoothly)
 				if imax == 0 then
-					local x0 = math.max(r_west, c_NW-zf, zf-c_SW)
-					local x1 = math.min(r_east, c_NE+zf, c_SE-zf)
-					local z0 = math.max(r_north, c_NW-xf, xf-c_NE)
-					local z1 = math.min(r_south, c_SW+xf, c_SE-xf)
+					local x0 = max(r_west, c_NW-zf, zf-c_SW)
+					local x1 = min(r_east, c_NE+zf, c_SE-zf)
+					local z0 = max(r_north, c_NW-xf, xf-c_NE)
+					local z1 = min(r_south, c_SW+xf, c_SE-xf)
 					xf = (xf-x0) / (x1-x0)
 					zf = (zf-z0) / (z1-z0)
 				elseif imax == 1 then
@@ -90,7 +94,7 @@ local function heightmaps(minp, maxp)
 
 				-- Determine elevation by interpolation
 				local vdem = poly.dem
-				local terrain_height = math.floor(0.5+interp(
+				local terrain_height = floor(0.5+interp(
 					vdem[1],
 					vdem[2],
 					vdem[3],
@@ -115,10 +119,10 @@ local function heightmaps(minp, maxp)
 						lake_id = 1
 					end
 				end
-				local lake_height = math.max(math.floor(poly.lake[lake_id]), terrain_height)
+				local lake_height = max(floor(poly.lake[lake_id]), terrain_height)
 
 				if imax > 0 and depth_factor_max > 0 then
-					terrain_height = math.min(math.max(lake_height, sea_level) - math.floor(1+depth_factor_max*riverbed_slope), terrain_height)
+					terrain_height = min(max(lake_height, sea_level) - floor(1+depth_factor_max*riverbed_slope), terrain_height)
 				end
 
 				terrain_height_map[i] = terrain_height
diff --git a/init.lua b/init.lua
index 89065eb..71b1e15 100644
--- a/init.lua
+++ b/init.lua
@@ -32,6 +32,9 @@ local function interp(v00, v01, v11, v10, xf, zf)
 	return v1*zf + v0*(1-zf)
 end
 
+-- Localize for performance
+local floor, min = math.floor, math.min
+
 local data = {}
 
 local noise_x_obj, noise_z_obj, noise_distort_obj, noise_heat_obj, noise_heat_blend_obj
@@ -111,8 +114,8 @@ local function generate(minp, maxp, seed)
 			end
 		end
 
-		local pminp = {x=math.floor(xmin), z=math.floor(zmin)}
-		local pmaxp = {x=math.floor(xmax)+1, z=math.floor(zmax)+1}
+		local pminp = {x=floor(xmin), z=floor(zmin)}
+		local pmaxp = {x=floor(xmax)+1, z=floor(zmax)+1}
 		incr = pmaxp.x-pminp.x+1
 		i_origin = 1 - pminp.z*incr - pminp.x
 		terrain_map, lake_map = heightmaps(pminp, pmaxp)
@@ -145,7 +148,7 @@ local function generate(minp, maxp, seed)
 
 	for z = minp.z, maxp.z do
 		for x = minp.x, maxp.x do
-			local ivm = a:index(x, minp.y, z)
+			local ivm = a:index(x, maxp.y+1, z)
 			local ground_above = false
 			local temperature
 			if use_biomes then
@@ -161,8 +164,8 @@ local function generate(minp, maxp, seed)
 				if use_distort then
 					local xn = noise_x_map[nid]
 					local zn = noise_z_map[nid]
-					local x0 = math.floor(xn)
-					local z0 = math.floor(zn)
+					local x0 = floor(xn)
+					local z0 = floor(zn)
 
 					local i0 = i_origin + z0*incr + x0
 					local i1 = i0+1
@@ -170,13 +173,12 @@ local function generate(minp, maxp, seed)
 					local i3 = i2-1
 
 					terrain = interp(terrain_map[i0], terrain_map[i1], terrain_map[i2], terrain_map[i3], xn-x0, zn-z0)
-					lake = math.min(lake_map[i0], lake_map[i1], lake_map[i2], lake_map[i3])
+					lake = min(lake_map[i0], lake_map[i1], lake_map[i2], lake_map[i3])
 				end
 
 				if y <= maxp.y then
 
 					local is_lake = lake > terrain
-					local ivm = a:index(x, y, z)
 					if y <= terrain then
 						if not use_biomes or y <= terrain-1 or ground_above then
 							data[ivm] = c_stone
@@ -205,7 +207,7 @@ local function generate(minp, maxp, seed)
 
 				ground_above = y <= terrain
 
-				ivm = ivm + ystride
+				ivm = ivm - ystride
 				if use_distort then
 					nid = nid + incrY
 				end
diff --git a/polygons.lua b/polygons.lua
index 0cb4c45..9f38983 100644
--- a/polygons.lua
+++ b/polygons.lua
@@ -90,16 +90,19 @@ if mapgen_rivers.settings.center then
 	map_offset.z = blocksize*Z/2
 end
 
+-- Localize for performance
+local floor, ceil, min, max, abs = math.floor, math.ceil, math.min, math.max, math.abs
+
 local min_catchment = mapgen_rivers.settings.min_catchment / (blocksize*blocksize)
 local wpower = mapgen_rivers.settings.river_widening_power
 local wfactor = 1/(2*blocksize * min_catchment^wpower)
 local function river_width(flow)
-	flow = math.abs(flow)
+	flow = abs(flow)
 	if flow < min_catchment then
 		return 0
 	end
 
-	return math.min(wfactor * flow ^ wpower, 1)
+	return min(wfactor * flow ^ wpower, 1)
 end
 
 local noise_heat -- Need a large-scale noise here so no heat blend
@@ -138,8 +141,8 @@ local function make_polygons(minp, maxp)
 
 	local polygons = {}
 	-- Determine the minimum and maximum coordinates of the polygons that could be on the chunk, knowing that they have an average size of 'blocksize' and a maximal offset of 0.5 blocksize.
-	local xpmin, xpmax = math.max(math.floor((minp.x+map_offset.x)/blocksize - 0.5), 0), math.min(math.ceil((maxp.x+map_offset.x)/blocksize + 0.5), X-2)
-	local zpmin, zpmax = math.max(math.floor((minp.z+map_offset.z)/blocksize - 0.5), 0), math.min(math.ceil((maxp.z+map_offset.z)/blocksize + 0.5), Z-2)
+	local xpmin, xpmax = max(floor((minp.x+map_offset.x)/blocksize - 0.5), 0), min(ceil((maxp.x+map_offset.x)/blocksize + 0.5), X-2)
+	local zpmin, zpmax = max(floor((minp.z+map_offset.z)/blocksize - 0.5), 0), min(ceil((maxp.z+map_offset.z)/blocksize + 0.5), Z-2)
 
 	-- Iterate over the polygons
 	for xp = xpmin, xpmax do
@@ -165,8 +168,8 @@ local function make_polygons(minp, maxp)
 
 			local bounds = {} -- Will be a list of the intercepts of polygon edges for every Z position (scanline algorithm)
 			-- Calculate the min and max Z positions 
-			local zmin = math.max(math.floor(math.min(unpack(poly_z)))+1, minp.z)
-			local zmax = math.min(math.floor(math.max(unpack(poly_z))), maxp.z)
+			local zmin = max(floor(min(unpack(poly_z)))+1, minp.z)
+			local zmax = min(floor(max(unpack(poly_z))), maxp.z)
 			-- And initialize the arrays
 			for z=zmin, zmax do
 				bounds[z] = {}
@@ -176,14 +179,14 @@ local function make_polygons(minp, maxp)
 			for i2=1, 4 do -- Loop on 4 edges
 				local z1, z2 = poly_z[i1], poly_z[i2]
 				-- Calculate the integer Z positions over which this edge spans
-				local lzmin = math.floor(math.min(z1, z2))+1
-				local lzmax = math.floor(math.max(z1, z2))
+				local lzmin = floor(min(z1, z2))+1
+				local lzmax = floor(max(z1, z2))
 				if lzmin <= lzmax then -- If there is at least one position in it
 					local x1, x2 = poly_x[i1], poly_x[i2]
 					-- Calculate coefficient of the equation defining the edge: X=aZ+b
 					local a = (x1-x2) / (z1-z2)
 					local b = (x1 - a*z1)
-					for z=math.max(lzmin, minp.z), math.min(lzmax, maxp.z) do
+					for z=max(lzmin, minp.z), min(lzmax, maxp.z) do
 						-- For every Z position involved, add the intercepted X position in the table
 						table.insert(bounds[z], a*z+b)
 					end
@@ -194,11 +197,11 @@ local function make_polygons(minp, maxp)
 				-- Now sort the bounds list
 				local zlist = bounds[z]
 				table.sort(zlist)
-				local c = math.floor(#zlist/2)
+				local c = floor(#zlist/2)
 				for l=1, c do
 					-- Take pairs of X coordinates: all positions between them belong to the polygon.
-					local xmin = math.max(math.floor(zlist[l*2-1])+1, minp.x)
-					local xmax = math.min(math.floor(zlist[l*2]), maxp.x)
+					local xmin = max(floor(zlist[l*2-1])+1, minp.x)
+					local xmax = min(floor(zlist[l*2]), maxp.x)
 					local i = (z-minp.z) * chulens + (xmin-minp.x) + 1
 					for x=xmin, xmax do
 						-- Fill the map at these places
@@ -220,16 +223,16 @@ local function make_polygons(minp, maxp)
 			local riverD = river_width(rivers[iD])
 			if glaciers then -- Widen the river
 				if get_temperature(poly_x[1], poly_dem[1], poly_z[1]) < 0 then
-					riverA = math.min(riverA*glacier_factor, 1)
+					riverA = min(riverA*glacier_factor, 1)
 				end
 				if get_temperature(poly_x[2], poly_dem[2], poly_z[2]) < 0 then
-					riverB = math.min(riverB*glacier_factor, 1)
+					riverB = min(riverB*glacier_factor, 1)
 				end
 				if get_temperature(poly_x[3], poly_dem[3], poly_z[3]) < 0 then
-					riverC = math.min(riverC*glacier_factor, 1)
+					riverC = min(riverC*glacier_factor, 1)
 				end
 				if get_temperature(poly_x[4], poly_dem[4], poly_z[4]) < 0 then
-					riverD = math.min(riverD*glacier_factor, 1)
+					riverD = min(riverD*glacier_factor, 1)
 				end
 			end