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hyphenrf's solution

to Leap in the MIPS Assembly Track

Published at Jul 26 2020 · 0 comments
Test suite

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.


Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.


JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


# Test is_leap_year with some examples
# s0 - num of tests left to run
# s1 - address of input word
# s2 - address of expected output word
# s3 - input word
# s4 - output word
# is_leap_year must:
# - be named is_leap_year and declared as global
# - read input integer from a0
# - follow the convention of using the t0-9 registers for temporary storage
# - (if it wants to use s0-7 then it is responsible for pushing existing values to the stack then popping them back off before returning)
# - write boolean result to v0


n: .word 7                      # number of test cases
ins:  .word 1996, 1997, 1998, 1900, 1800, 2400, 2000  # input years
outs: .word    1,    0,    0,    0,    0,    1,    1  # expected result

failmsg: .asciiz "failed for test input: "
okmsg: .asciiz "all tests passed"


        lw      $s0, n
        la      $s1, ins
        la      $s2, outs

        lw      $s3, 0($s1)             # read input from memory
        move    $a0, $s3                # move it to a0
        jal     is_leap_year            # call subroutine under test
        move    $v1, $v0                # move return value in v0 to v1 because we need v0 for syscall

        lw      $s4, 0($s2)             # read expected output from memory
        bne     $v1, $s4, exit_fail     # if expected doesn't match actual, jump to fail

        addi    $s1, $s1, 4             # move to next word in input
        addi    $s2, $s2, 4             # move to next word in output
        sub     $s0, $s0, 1             # decrement num of tests left to run
        bgt     $s0, $zero, run_test    # if more than zero tests to run, jump to run_test

        la      $a0, okmsg              # put address of okmsg into a0
        li      $v0, 4                  # 4 is print string

        li      $v0, 10                 # 10 is exit with zero status (clean exit)

        la      $a0, failmsg            # put address of failmsg into a0
        li      $v0, 4                  # 4 is print string

        move    $a0, $s3                # set arg of syscall to input that failed the test
        li      $v0, 1                  # 1 is print int

        li      $a0, 1                  # set exit code to 1
        li      $v0, 17                 # terminate with the exit code in $a0

# # Include your implementation here if you wish to run this from the MARS GUI.
# .include "impl.mips"
.globl is_leap_year

.macro modzero($check, $jump)
	li    $t0, $check #400, 100, 4
	div   $a0, $t0
	mfhi  $t0         #0 if divisible
	beqz  $t0, $jump  #if divisible, branch

	modzero(400, leap)
	modzero(100, norm)
	modzero(4,   leap)
	li    $v0, 0
	jr    $ra
	li    $v0, 1
	jr    $ra

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