Arrays and Pointers Variables are just names of memory locations An array is a variable just with many memory locations all contiguous Address pointer in function not C syntax Address pointer in assembler no data typing Allocating an Array You have to know the size in bytes of each element of the array Int 4 bytes Float 4 bytes Char 1 byte Determine the number of bytes needed Size quantity Allocate space in bytes arr space 100 Memory Access Remember the REAL assembly language can only access memory via number R Or disp base where disp is a number and base is a register The address is the value in the base register added to the displacement The la command The la load address macro command is very helpful especially with arrays We will load the address of the data section The data section always starts at memory location x10010000 Look at the first 4 hex char x1001 This is 4097 in decimal The lui command Used by the assembler a lot Some instructions only have a 16 bit operand To get a 32 bit value into a register we need two instruction lui load upper immediate Loads the upper 2 bytes 16 bits of the register with the specified value and places 0 s in the last 16 bits ori or immediate logically or s the last 16 bits of a register with the immediate operand Back to the la So to load the 32 bit address of a variable into t1 the assembler uses lui t1 4097 now t1 has the addr of the data section ori t1 offset the distance the var is from the beginning of the data This replaces the la t1 var instruction Working with Arrays First get the address of the array into a register la t1 arr To get to element i of an array you multiply i by the size of an element and add that to the base address of the array This gives the address of arr i Processing an entire array If you are looping through an array rather than multiply you could just add the size of an element to the current address to get the address of the next element Example for i 0 i 25 i arr i i In assembler In the data section arr space100 In the text section la t1 arr li t2 0 li t3 25 loop beq t2 t3 done sw t2 0 t1 addi t1 4 addi t2 1 j loop done i limit address increases by 4 counter increases by 1 Other examples Look at the reverse string example Look at the binary search example Look at the sorting example