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.global is_alpha, is_digit, is_alnum, write_out, read_file, exit
.section .rodata
.equ SYS_READ, 63
.equ SYS_WRITE, 64
.equ SYS_EXIT, 93
.equ STDIN, 0
.equ STDOUT, 1
.equ STDERR, 2
.section .text
# 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:
li t0, 'A' - 1
sltu t1, t0, a0 # t1 = a0 >= 'A'
sltiu t2, a0, 'Z' + 1 # t2 = a0 <= 'Z'
and t1, t1, t2 # t1 = a0 >= 'A' & a0 <= 'Z'
li t0, 'a' - 1
sltu t2, t0, a0 # t2 = a0 >= 'a'
sltiu t3, a0, 'z' + 1 # t3 = a0 <= 'z'
and t2, t2, t3 # t2 = a0 >= 'a' & a0 <= 'z'
xori t3, a0, '_'
seqz t3, t3
or a0, t1, t2
or a0, a0, t3
ret
.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, @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.
exit:
li a7, SYS_EXIT
ecall
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