fixed a bug with the multiply function in core.dsa and added a print_num

function to print.dsa for decimal numbers

resources/dsa/lib/io/print.dsa

@@ -28,6 +28,11 @@
 //      push pcx
 //      jmp print::print_word
 //
+// usage for print_num:
+//      push (register containing number to print in decimal)
+//      push pcx
+//      jmp print::print_num
+//
 
 include maths "../maths/core.dsa"
 
@@ -209,6 +214,65 @@ print_newline:
     // _end saves the display state
     jmp _end
 
+// ------------------------------------------
+// prints arg[0] as a decimal number to the screen.
+print_num:
+    push bpr
+    mov spr, bpr
+
+    ldw bpr, rg0, 8      // load number to print
+    lli 0, rg5           // rg5 = digit counter
+
+    // check if number is zero
+    cmp rg0, zero
+    jne _print_num_extract_digits
+
+    // special case: print '0' for zero
+    lli 0x30, rg6
+    push rg6             // push digit to stack buffer
+    lli 1, rg5           // we have 1 digit
+    jmp _print_num_output
+
+_print_num_extract_digits:
+    // divide by 10 repeatedly to get digits
+    cmp rg0, zero
+    jeq _print_num_output
+
+    // call divmod(rg0, 10)
+    push rg0             // dividend
+    lli 10, rg1
+    push rg1             // divisor (10)
+    call maths::divmod
+    pop rg0              // quotient (continue dividing this)
+    pop rg1              // remainder (the digit)
+
+    // convert digit to ASCII and push to stack buffer
+    addi rg1, 0x30, rg6  // convert to ASCII
+    push rg6             // push digit to stack
+    inc rg5              // increment digit counter
+
+    jmp _print_num_extract_digits
+
+_print_num_output:
+    // now print digits (pop them off in reverse order)
+    ldw current, rg1     // get display pointer
+
+_print_num_output_loop:
+    // check if we've printed all digits
+    cmp rg5, zero
+    jeq _print_num_done
+
+    // pop digit and print it
+    pop rg6
+    stb rg6, rg1
+    addi rg1, 1
+    dec rg5
+
+    jmp _print_num_output_loop
+
+_print_num_done:
+    jmp _end
+
 // ------------------------------------------
 // resets the cursor position on the screen to 0x20000. (0,0)
 reset:

resources/dsa/lib/maths/core.dsa

@@ -16,6 +16,7 @@ multiply:
 
 	ldw bpr, rg0, 8  // load op 2
 	ldw bpr, rg1, 12 // load op 1
+	lwi 0, rg2       // initialise rg2 to zero
 
 _multiply_loop:
 	add rg2, rg0, rg2