.equ SYS_WRITE, 64
.equ SYS_EXIT, 94
.equ STDOUT, 1
.equ SUCCESS, 0
	
.global _start                                                                                      

_start: 

	# The decrement
	li s2, 1
	# The final value 
	li s1, 1
	# The first value then the current value
	li s0, 100

loop:
	# Print the current value 
	add a0, zero, s0
	call num_print
	
	# Decrement
	sub s0, s0, s2

	# End of loop?
	ble s1, s0, loop # BLT : Branch If Lower Or Equal

	# Print the end-of-line
	li a0, STDOUT	
	la    a1, eol
        addi  a2, x0, 1
        addi  a7, x0, SYS_WRITE
	ecall

	# Exit
        li    x10, SUCCESS
        addi    x17, x0, SYS_EXIT
        ecall

# Written by code4eva <https://stackoverflow.com/questions/66941555/how-to-output-an-integer-to-screen-risc-v-assembly>
num_print:
	addi         sp, sp, -40      # create stack space
	sd           s0, 32(sp)       # store frame pointer
	addi         s0, sp, 40       # new frame pointer

	addi         t0, zero, 0      # initialize sign_bit
	addi         t1, zero, 10     # divisor and new-line char
	addi         t2, s0, -16      # t2: string[n]
	add          a1, zero, t2     # a1: string[0] currently string[n]

	addi         t3, zero, '\n'   # '\n' char
	sb           t3, 0(a1)        # store '\n'

	bge          a0, zero, PVE    # if num >= 0 go to L1 else get absolute
	xori         a0, a0, -1       # (num ^ -1)
	addi         a0, a0, 1        # num + 1
	addi         t0, zero, 1      # set sign-bit to 1

PVE:
	remu         t3, a0, t1       # num % 10
	addi         t3, t3, 48       # convert to ascii
	addi         a1, a1, -1       # decrement start pointer
	sb           t3, 0(a1)        # store value
	divu         a0, a0, t1       # num /= 10
	blt          zero, a0, PVE    # if num > 0 loop

	beq          t0, zero, print  # if sign_bit = 0 go to print else, add '-' char
	addi         t3, zero, '-'    # ascii '-'
	addi         a1, a1, -1       # decrement start pointer
	sb           t3, 0(a1)        # store '-'

print:
	sub          t4, t2, a1       # t4: len -- string[n] - string[0]
	addi         a2, t4, 1        # len + 1
	addi         a0, zero, 1      # file descriptor to write to
	addi         a7, zero, 64     #  pk SYS_write
	ecall                         # transfer control to os

	ld           s0, 32(sp)       # restore frame pointer
	addi         sp, sp, 40       # restore stack pointer

	ret                           # return from function
	
.data
eol:      .ascii "\n"