Print numbers with multiple digits

tools/builtin.s

@@ -6,29 +6,41 @@
 
 .text
 printi:
-    addi sp, sp, -4
+    addi sp, sp, -16
     sw s0, 0(sp)
     sw ra, 4(sp)
-    addi s0, sp, 4
+    addi s0, sp, 16
+
+    addi t1, zero, '\n'
+    sb t1, -1(s0)
+
+    # t0 - Whole number.
+    # t1 - Constant 10.
+    # a1 - Local buffer.
+    # t2 - Current character.
+    lw t0, 0(s0)
+    addi t1, zero, 10
+    addi a1, s0, -2
+
+.digit10:
+    rem t2, t0, t1
+    addi t2, t2, '0'
+    sb t2, 0(a1)
+    div t0, t0, t1
+    addi a1, a1, -1
+    bne zero, t0, .digit10
 
-    addi t0, a0, 0
-    addi a0, a0, '0'
-    sw a0, 0(s0)
-    addi a0, x0, 1
-    addi a1, s0, 0
-    addi a2, x0, 1
-    addi a7, x0, 64
     ecall
 
-    addi t1, x0, '\n'
-    sw t1, 0(s0)
+    addi a0, zero, 1
+    addi a1, a1, 1
+    sub a2, s0, a1
+    addi a7, zero, 64
     ecall
 
-    addi a0, t0, 0
-
     lw s0, 0(sp)
     lw ra, 4(sp)
-    addi sp, sp, 4
+    addi sp, sp, 16
     ret
 
 _start: