/*****************************************************************************
*
* Name: v_dec_orig
*
* Description: display numbers in decimal
*
* From Chapter 7 of "Assembly Language Using the Raspberry Pi" by Robert Dunne
* Pages: 151 - 168
*
* Author: 
* Date:
*
*------|-------|----------------|----------------------------------------------
*
******************************************************************************/

	.global _start

_start:	mov	r0, #125	 // An arbitrary sample decimal value for test
	bl	v_dec		 // Call subroutine to view dec value in R0 in
				 // ASCI
	mov	r0, #0		 // Exit status code
	mov 	r7, #1		 // service command to terminate program
	svc	0		 // Issue Linux command to terminate program

/*
  Subroutine v_dec will display a 32-bit register in decimal digits

  	r0	: contains number to be displayed
		  if negative (bit 31 = 1), then a minus sign will be output
	lr	: contains return address

	ALL REGISTER CONTENTS WILL BE PRESERVED
*/

v_dec:	push 	{r0 - r7}	 // Save contents of registers r0 through r7
	mov	r3, r0		 // r3 will hold a copy of input word to be
				 // displayed
	mov	r2, #1		 // number of characters to display at a time
	mov     r0, #1		 // code for standard output
	mov     r7, #4		 // Linux service command to write string

// If bit 31 is set, then register contains a negative number and "-" should
// be output.

	cmp	r3, #0		 // determin if minus sign is needed
	bge	absval		 // if positive number, then display it
	ldr	r1, =msign	 // address of minus sign in memory
	svc	0		 // service call to write string out to stdout

	rsb	r3, r3, #0	 // get absolute value (negative of negative)
				 // for display

/*
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*/