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.syntax unified
.cpu cortex-m0plus
.thumb
.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}
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