add Mult.asm

projects/04/mult/Mult.asm

@@ -0,0 +1,57 @@
+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/04/Mult.asm
+
+// Multiplies R0 and R1 and stores the result in R2.
+// (R0, R1, R2 refer to RAM[0], RAM[1], and RAM[2], respectively.)
+//
+// This program only needs to handle arguments that satisfy
+// R0 >= 0, R1 >= 0, and R0*R1 < 32768.
+
+// Put your code here.
+
+// variable names are selfexplanatory
+// itr temporary register at RAM[16]
+// sum temporary register at RAM[17]
+@itr
+M=0
+@sum
+M=0
+
+// loop declaration
+// D = R1 - itr
+// if 0 jump to @STOP
+// else continue
+    (LOOP)
+@itr
+D=M
+@R1
+D=D-M
+@STOP
+D;JEQ
+
+// sum = R0 + sum
+// itr = itr + 1
+@R0
+D=M
+@sum
+M=D+M
+@itr
+M=M+1
+
+// back to loop declaration
+@LOOP
+0;JMP
+
+// R2 = sum
+    (STOP)
+@sum
+D=M
+@R2
+M=D
+
+// loopy loop
+    (END)
+@END
+0;JMP