Homework 0

HW0/Makefile

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+all:
+	gcc -m32 -o read-write read-write.s
+
+clean:
+	rm -f read-write

HW0/read-write.s

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+.section .data
+inp_buf: .byte 0
+
+.section .text
+
+.globl main
+#    /*; System call to read from standard input into buffer
+#    ;            eax= code of syscall (read = 3)
+#    ; Arguments: ebx= file descriptor (0 is stdin)
+#    ;            ecx= pointer to buffer
+#    ;            edx= maximum number of bytes to read
+#    ; Return value: eax= number of bytes read*/
+main:
+    # Read into buffer
+    mov $3, %eax
+    mov $0, %ebx
+    mov $inp_buf, %ecx
+    mov $1, %edx
+    int $0x80
+
+    # Transform from ascii to int
+    sub $0x30, (inp_buf)
+
+    mov (inp_buf), %esi
+
+loop:
+    # Read new value
+    mov $3, %eax
+    mov $0, %ebx
+    mov $inp_buf, %ecx
+    mov $1, %edx
+    int $0x80
+    # if non number, jump to end
+    cmp $0xA, (inp_buf)
+    je end
+    # Substract 0x30
+    sub $0x30, (inp_buf)
+    # Multiply esi by 10
+    imul $10, %esi
+    # Add value to esi
+    add (inp_buf), %esi
+    jmp loop
+end:# Print result
+
+    add $1, %esi
+    mov %esi, %eax
+
+    xorl %esi, %esi
+
+loop2:
+    movl $0, %edx
+    movl $10, %ebx
+    divl %ebx
+    addl $48, %edx
+    push %edx
+    incl %esi
+    cmpl $0, %eax
+    jz   next
+    jmp loop2
+
+next:
+    cmpl $0, %esi
+    jz   exit
+    decl %esi
+    movl $4, %eax
+    movl %esp, %ecx
+    movl $1, %ebx
+    movl $1, %edx
+    int  $0x80
+    addl $4, %esp
+    jmp  next
+
+exit: