Use absolute branches for subroutine calls

1 files changed, 48 insertions, 68 deletions

diff --git a/assembler/octal.s b/assembler/octal.s
index 18abebd..62e2b1e 100644
--- a/assembler/octal.s
+++ b/assembler/octal.s
@@ -5,71 +5,51 @@
 .type octal, %function
 .global octal
 
-octal:
-  PUSH {LR}
-  MOVS R5, R0
-
-  // Handle bit-width = 0
-  BNE 30f
-10:
-  BL get_char
-  CMP R0, '0
-  BNE 10b
-  BL uart_send
-  MOVS R4, 0
-20:
-  BL get_char
-  BNE 20b
-  POP {PC}
-30:
-
-  // R4 will become '1 or '3 or '7
-  MOVS R0, 3
-  CMP R5, 3
-  BHS 40f
-  MOVS R0, R5
-40:
-  MOVS R4, 1
-  LSLS R4, R0
-  ADDS R4, ('0 - 1)
-
-  // Get first char
-50:
-  BL get_char
-  CMP R0, '0
-  BLO 50b
-  CMP R0, R4
-  BHI 50b
-  BL uart_send
-  SUBS R0, '0
-  MOVS R4, R0
-
-  // Subtract 1, 2, or 3 from bit-width
-  MOVS R1, 0
-60:
-  ADDS R1, 1
-  LSRS R0, 1
-  BNE 60b
-  SUBS R5, R1
-
-  // Loop for remaining chars
-70:
-  CMP R5, 3
-  BLO 80f
-  BL get_char
-  BEQ 90f
-  CMP R0, '0
-  BLO 70b
-  CMP R0, '7
-  BHI 70b
-  BL uart_send
-  SUBS R0, '0
-  LSLS R4, 3
-  ADDS R4, R0
-  SUBS R5, 3
-  B 70b
-80:
-  BL get_char
-  BNE 80b
-90:
-  POP {PC}
+octal:  PUSH    {LR}            // 0c0000 0xB500  ; SAVE LINK REGISTER
+        MOVS    R5, R0          // 0x0002 0x0005  ; SAVE BIT WIDTH
+        BNE     30f             // 0x0004 0xD1    ; SKIP IF BIT WIDTH != 0
+10:     BLX     R10             // 0x0006 0x      ; GET CHAR
+        CMP     R0, '0          // 0x000A 0x2830  ; COMPARE TO '0 CHAR
+        BNE     10b             // 0x000C 0xD1    ; GET ANOTHER CHAR IF NOT '0
+        BLX     R9              // 0x000E 0x      ; OTHERWISE ECHO '0 CHAR
+        MOVS    R4, 0           // 0x0012 0x2400  ; SET RESULT TO 0
+20:     BLX     R10             // 0x0014 0x      ; GET CHAR
+        BNE     20b             // 0x0018 0xD1    ; LOOP IF NOT END CHAR
+        POP     {PC}            // 0x001A 0xBD00  ; RETURN IF END CHAR
+30:     MOVS    R0, 3           // 0x001C 0x2003  ; DEFAULT TO 3
+        CMP     R5, 3           // 0x001E 0x2D03  ; CHECK BIT WIDTH
+        BHS     40f             // 0x0020 0xD2    ; IF BIT WIDTH >= 3 KEEP R0 == 3
+        MOVS    R0, R5          // 0x0022 0x0028  ; IF BIT WIDTH < 3 COPY TO R0
+40:     MOVS    R4, 1           // 0x0024 0x2401  ; 2^0
+        LSLS    R4, R0          // 0x0026 0x4084  ; 2^(MAX(BIT WIDTH, 3))
+        ADDS    R4, ('0 - 1)    // 0x0028 0x342F  ; '1 OR '3 or '7
+50:     BLX     R10             // 0x002A 0x      ; GET FIRST CHAR
+        CMP     R0, '0          // 0x002E 0x2830  ; COMPARE WITH '0
+        BLO     50b             // 0x0030 0xD3    ; RETRY IF BELOW OCTAL RANGE
+        CMP     R0, R4          // 0x0032 0x42A0  ; COMPARE WITH END CHAR
+        BHI     50b             // 0x0034 0xD8    ; RETRY IF ABOVE RANGE
+        BLX     R9              // 0x0036 0x      ; ECHO IF IN RANGE
+        SUBS    R0, '0          // 0x003A 0x3830  ; GET VALUE FROM CHAR
+        MOVS    R4, R0          // 0x003C 0x0004  ; STORE VALUE IN RESULT
+        MOVS    R1, 0           // 0x003E 0x2100  ; BIT WIDTH FOR FIRST CHAR
+60:     ADDS    R1, 1           // 0x0040 0x3101  ; INCREMENT FIRST CHAR WIDTH
+        LSRS    R0, 1           // 0x0042 0x0840  ; SHIFT RIGHT ONE BIT
+        BNE     60b             // 0x0044 0x      ; IF NONZERO STAY IN LOOP
+        SUBS    R5, R1          // 0x0046 0x1A6D  ; SUBTRACT FIRST CHAR WIDTH FROM TOTAL
+70:     CMP     R5, 3           // 0x0048 0x2D03  ; COMPARE BIT WIDTH TO 3
+        BLO     80f             // 0x004A 0xD3    ; EXIT LOOP IF LESS THAN 3
+        BLX     R10             // 0x004C 0x      ; GET ANOTHER CHAR
+        BEQ     90f             // 0x0050 0xD0    ; IF END CHAR EXIT LOOP
+        CMP     R0, '0          // 0x0052 0x2830  ; BOTTOM OF OCTAL RANGE
+        BLO     70b             // 0x0054 0xD3    ; RETRY IF BELOW
+        CMP     R0, '7          // 0x0056 0x2837  ; TOP OF OCTAL RANGE
+        BHI     70b             // 0x0058 0xD8    ; RETRY IF ABOVE
+        BLX     R9              // 0x005A 0x      ; ECHO IF IN RANGE
+        SUBS    R0, '0          // 0x005E 0x3830  ; GET VALUE FROM CHAR
+        LSLS    R4, 3           // 0x0060 0x00E4  ; SHIFT OLD VALUE BY ONE DIGIT
+        ADDS    R4, R0          // 0x0062 0x1824  ; ACCUMULATE INTO VALUE
+        SUBS    R5, 3           // 0x0064 0x3D03  ; DECREMENT BIT WIDTH BY 3
+        B       70b             // 0x0066 0xD0    ; LOOP FOR ANOTHER DIGIT
+80:     BLX     R10             // 0x0068 0x      ; GET A CHAR
+        BNE     80b             // 0x006C 0xD1    ; LOOP UNTIL END CHAR
+90:     POP     {PC}            // 0x006E 0xBD00  ; RETURN