path: root/boot/common-boot.s

.global _is_alpha, _is_digit, _is_alnum, _is_upper, _is_lower
.global _write_out, _read_file, _memcmp, _write_error, _put_char, _printi
.global _divide_by_zero_error, _exit

.section .rodata

.equ SYS_READ, 63
.equ SYS_WRITE, 64
.equ SYS_EXIT, 93
.equ STDIN, 0
.equ STDOUT, 1
.equ STDERR, 2

new_line: .ascii "\n"

.section .text

# Write the current token to stderr.
# a0 - String pointer.
# a1 - String length.
.type _write_error, @function
_write_error:
	mv t0, a0
	mv t1, a1

	li a0, STDERR
	mv a1, t0
	mv a2, t1
	li a7, SYS_WRITE
	ecall

	li a0, STDERR
	la a1, new_line
	li a2, 1
	li a7, SYS_WRITE
	ecall

	ret

# a0 - First pointer.
# a1 - Second pointer.
# a2 - The length to compare.
#
# Returns 0 in a0 if memory regions are equal.
.type _memcmp, @function
_memcmp:
	mv t0, a0
	li a0, 0

.Lmemcmp_loop:
	beqz a2, .Lmemcmp_end

	lbu t1, (t0)
	lbu t2, (a1)
	sub a0, t1, t2

	bnez a0, .Lmemcmp_end

	addi t0, t0, 1
	addi a1, a1, 1
	addi a2, a2, -1

	j .Lmemcmp_loop

.Lmemcmp_end:
	ret

# Detects if a0 is an uppercase character. Sets a0 to 1 if so, otherwise to 0.
.type _is_upper, @function
_is_upper:
	li t0, 'A' - 1
	sltu t1, t0, a0 # t1 = a0 >= 'A'

	sltiu t2, a0, 'Z' + 1 # t2 = a0 <= 'Z'
	and a0, t1, t2 # t1 = a0 >= 'A' & a0 <= 'Z'

	ret

# Detects if a0 is an lowercase character. Sets a0 to 1 if so, otherwise to 0.
.type _is_lower, @function
_is_lower:
	li t0, 'a' - 1
	sltu t2, t0, a0 # t2 = a0 >= 'a'

	sltiu t3, a0, 'z' + 1 # t3 = a0 <= 'z'
	and a0, t2, t3 # t2 = a0 >= 'a' & a0 <= 'z'

	ret

# Detects if the passed character is a 7-bit alpha character or an underscore.
# The character is passed in a0.
# Sets a0 to 1 if the character is an alpha character or underscore, sets it to 0 otherwise.
.type _is_alpha, @function
_is_alpha:
	# Prologue.
	addi sp, sp, -16
	sw ra, 12(sp)
	sw s0, 8(sp)
	addi s0, sp, 16

	sw a0, 4(sp)

	call _is_upper
	sw a0, 0(sp)

	lw a0, 4(sp)
	call _is_lower

	lw t0, 4(sp)
	xori t1, t0, '_'
	seqz t1, t1

	lw t0, 0(sp)
	or a0, a0, t0
	or a0, a0, t1

	# Epilogue.
	lw ra, 12(sp)
	lw s0, 8(sp)
	addi sp, sp, 16
	ret

# Detects whether the passed character is a digit
# (a value between 0 and 9).
#
# Parameters:
# a0 - Exemined value.
#
# Sets a0 to 1 if it is a digit, to 0 otherwise.
.type _is_digit, @function
_is_digit:
	li t0, '0' - 1
	sltu t1, t0, a0 # t1 = a0 >= '0'

	sltiu t2, a0, '9' + 1 # t2 = a0 <= '9'

	and a0, t1, t2

	ret

.type _is_alnum, @function
_is_alnum:
	# Prologue.
	addi sp, sp, -16
	sw ra, 12(sp)
	sw s0, 8(sp)
	addi s0, sp, 16

	sw a0, 4(sp)

	call _is_alpha
	sw a0, 0(sp)

	lw a0, 4(sp)
	call _is_digit

	lw a1, 0(sp)
	or a0, a0, a1

	# Epilogue.
	lw ra, 12(sp)
	lw s0, 8(sp)
	addi sp, sp, 16
	ret

.type _write_out, @function
_write_out:
	# Prologue.
	addi sp, sp, -8
	sw ra, 4(sp)
	sw s0, 0(sp)
	addi s0, sp, 8

	mv a2, a1
	mv a1, a0
	li a0, STDOUT
	li a7, SYS_WRITE
	ecall

	# Epilogue.
	lw ra, 4(sp)
	lw s0, 0(sp)
	addi sp, sp, 8
	ret

# Reads standard input into a buffer.
# a0 - Buffer pointer.
# a1 - Buffer size.
#
# Returns the result in a0.
.type _read_file, @function
_read_file:
	# Prologue.
	addi sp, sp, -8
	sw ra, 4(sp)
	sw s0, 0(sp)
	addi s0, sp, 8

	mv a2, a1
	mv a1, a0
	li a0, STDIN
	li a7, SYS_READ
	ecall

	# Epilogue.
	lw ra, 4(sp)
	lw s0, 0(sp)
	addi sp, sp, 8
	ret

# Terminates the program. a0 contains the return code.
#
# Parameters:
# a0 - Status code.
.type _exit, @function
_exit:
	li a7, SYS_EXIT
	ecall
	# ret

.type _divide_by_zero_error, @function
_divide_by_zero_error:
    addi a7, zero, 172 # getpid
    ecall

    addi a1, zero, 8 # SIGFPE
    addi a7, zero, 129 # kill
    ecall
    ret

# a0 - Whole number.
# t1 - Constant 10.
# a1 - Local buffer.
# t2 - Current character.
# t3 - Whether the number is negative.
.type printi, @function
_printi:
    addi sp, sp, -16
    sw s0, 0(sp)
    sw ra, 4(sp)
    addi s0, sp, 16
    addi t1, zero, 10
    addi a1, s0, -1

    addi t3, zero, 0
    bge a0, zero, .digit10
    addi t3, zero, 1
    sub a0, zero, a0

.digit10:
    rem t2, a0, t1
    addi t2, t2, '0'
    sb t2, 0(a1)
    div a0, a0, t1
    addi a1, a1, -1
    bne zero, a0, .digit10

    beq zero, t3, .write_call
    addi t2, zero, '-'
    sb t2, 0(a1)
    addi a1, a1, -1

.write_call:
    addi a0, zero, 1
    addi a1, a1, 1
    sub a2, s0, a1
    addi a7, zero, 64 # write
    ecall

    lw s0, 0(sp)
    lw ra, 4(sp)
    addi sp, sp, 16
    ret

# Writes a character from a0 into the standard output.
.type _put_char, @function
_put_char:
	# Prologue
	addi sp, sp, -16
	sw ra, 12(sp)
	sw s0, 8(sp)
	addi s0, sp, 16

	sb a0, 4(sp)
	li a0, STDOUT
	addi a1, sp, 4
	li a2, 1
	li a7, SYS_WRITE
	ecall

	# Epilogue.
	lw ra, 12(sp)
	lw s0, 8(sp)
	add sp, sp, 16
	ret