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|
.section .data
;;;# Constants
.equ SYS_WRITE, 64
.equ SYS_BRK, 214
.equ STDOUT, 1
.equ NULL, 0
.section .text
;;;# size_t strlen(char *buf)
;;;# returns the lenght of buf
;;;# (buf must be a NULL-terminated)
;;;# returns 0 when buf is empty
.globl strlen
;;;# int puts(char *buf)
;;;# does a sys_write on buf
;;;# (buf must be a NULL-terminated)
;;;# returns the amount of charaters written
;;;# < 0 on fail
.globl puts
;;;# int putc(char ch)
;;;# does a sys_write on ch
;;;# returns 1 on success
.globl putc
;;;# int printf(char *buf, ...)
;;;# does what libc printf does
;;;# (buf must be NULL-terminated)
;;;# (the variadic args are on the stack
;;;# with the first begin at 0(sp))
;;;# returns the amount of characters written
;;;# < 0 on fail
.globl printf
;;;# strlen
strlen:
mv t0, a0 ;# copy buf addr
li t3, NULL ;# NULL
strlen_loop:
lb t2, 0(t0) ;# load cur char
beq t2, t3, strlen_end ;# end loop when its \0
addi t0, t0, 1 ;# next element in the array
j strlen_loop
strlen_end:
sub a0, t0, a0 ;# get the amount of elements
ret
;;;# puts
puts:
mv a1, a0 ;# copy buf
addi sp, sp, -4 ;# save ra
sw ra, 0(sp) ;#
call strlen
mv a2, a0 ;# move the len into a2
lw ra, 0(sp) ;# load ra
addi sp, sp, 4 ;#
li a7, SYS_WRITE
li a0, STDOUT
ecall
ret
;;;# putc
putc:
addi sp, sp, -1 ;# save the char on the stack
sb a0, 0(sp) ;# so it is an address
li a7, SYS_WRITE ;#
li a0, STDOUT ;#
mv a1, sp ;# do of write syscall
li a2, 1 ;#
ecall ;#
addi sp, sp, 1 ;# restore the stack
ret
;;;# printf
printf:
;;# using t6 and t5 like saved registers since i can't
;;# use the stack normally because of the variadic args
mv t6, zero ;# the character counter
mv t5, a0 ;# the fmt string
printf_loop:
lb t4, 0(t5) ;# load the next char
li t3, NULL ;# branch to end on null
beq t4, t3, printf_end ;#
li t3, '%' ;# branch on %
beq t4, t3, printf_on_fmt ;#
li t3, '\' ;# branch on escape character
beq t4, t3, printf_on_esc ;#
li a0, STDOUT ;#
mv a1, t5 ;# the character must be normal
li a2, 1 ;# so we just write it
li a7, SYS_WRITE ;#
ecall ;#
addi t6, t6, 1 ;# we wrote one more byte
printf_loop_again:
addi t5, t5, 1 ;# go to the next char
j printf_loop
printf_end:
mv a0, t6 ;# return the amount of written bytes
ret
;;;# each branch pops the data from the stack,
;;;# then it prints it and increases the byte counter (t6)
printf_on_fmt:
addi t5, t5, 1 ;# go to the next char
lb t4, 0(t5) ;# load the next char
li t3, NULL
beq t4, t3, printf_end ;# branch to end on null
li t3, '%'
beq t4, t3, printf_perc ;# print '%' on '%'
li t3, 's'
beq t4, t3, printf_string ;# print string on 's'
li t3, 'd'
beq t4, t3, printf_dec_num ;# print decimal on 'd'
j printf_loop_again ;# no such program character
;;;# each branch sets a0 to a char, then the char is written
printf_on_esc:
addi t5, t5, 1 ;# go to the next char
lb t4, 0(t5) ;# load the next char
li t3, NULL
beq t4, t3, printf_end ;# branch to end on null
li t3, '\'
beq t4, t3, printf_esc_slsh ;# putc slash
li t3, 'n'
beq t4, t3, printf_esc_nl ;# putc \n
printf_on_esc_ret:
addi sp, sp, -4 ;# push ra to the stack
sw ra, 0(sp) ;#
call putc
lw ra, 0(sp) ;# pop ra from the stack
addi sp, sp, 4 ;#
add t6, t6, a0 ;# add amount of printed chars
j printf_loop_again
printf_esc_slsh:
li a0, '\'
j printf_on_esc_ret
printf_esc_nl:
li a0, 0xA
j printf_on_esc_ret
printf_perc:
addi sp, sp, -4 ;# push ra to the stack
sw ra, 0(sp) ;#
li a0, '%' ;# putc '%'
call putc ;#
lw ra, 0(sp) ;# pop ra from the stack
addi sp, sp, 4 ;#
add t6, t6, a0 ;# add amount of printed chars
j printf_loop_again
printf_string:
lw a0, 0(sp) ;# get the string from the stack
sw ra, 0(sp) ;# save ra to stack
call puts
lw ra, 0(sp) ;# pop ra from the stack
addi sp, sp, 4 ;#
add t6, t6, a0 ;# add amount of printed chars
j printf_loop_again
printf_dec_num:
addi t0, zero, 10 ;# divisor
mv t2, zero ;# counter
lw t3, 0(sp) ;# pop the number from the stack
addi sp, sp, 4 ;#
printf_dec_num_loop:
remu t1, t3, t0 ;# get the last digit
addi t2, t2, 1 ;# inc the counter
addi t1, t1, '0' ;# turns digit into a char
addi sp, sp, -1 ;# one byte on stack
sb t1, 0(sp) ;# save on stack
divu t3, t3, t0 ;# remove the last digit
bne t3, zero, printf_dec_num_loop ;# loop again when the number is not 0
li a0, STDOUT ;#
mv a1, sp ;# do a write syscall
mv a2, t2 ;# on the string in the stack
li a7, SYS_WRITE ;#
ecall ;#
add sp, sp, t2 ;# clear the stack
add t6, t6, t2 ;# add to the char counter
j printf_loop_again
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