Create mergesort.lua

Author: abranhe

sorting/mergesort.lua

@@ -0,0 +1,55 @@
+
+--[[
+ Lua implementation of merge sort
+ 
+ Author: Carlos Abraham Hernandez (abraham@abranhe.com)
+--]]
+
+local function lt( x, y )
+	return x < y
+end
+
+return function( a, cmp, b, num, pad )
+	cmp, b, num, pad = cmp or lt, b or {}, num or #a, pad or 1
+	
+	local k = 1
+	while k < num do
+		for left = 0, num-k-1, k+k do
+			local rght = left + k
+			local rend = rght + k
+
+			if rend > num then
+				rend = num
+			end
+
+			local m, i, j = left, left, rght
+
+			while i < rght and j < rend do
+				if cmp( a[i+pad], a[j+pad] ) then
+					b[m+pad] = a[i+pad]
+					i = i + 1
+				else
+					b[m+pad] = a[j+pad]
+					j = j + 1
+				end
+				m = m + 1
+			end
+
+			while i < rght do
+				b[m+pad] = a[i+pad]
+				i, m = i + 1, m + 1
+			end
+
+			while j < rend do
+				b[m+pad] = a[j+pad]
+				j, m = j + 1, m + 1
+			end
+
+			for l = left, rend-1 do
+				a[l+pad] = b[l+pad]
+			end
+		end
+
+		k = k + k
+	end
+	return a