Updating the Repo

mips/binary/README.md

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+# Binary
+
+Write a program that will convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles
+
+Implement binary to decimal conversion. Given a binary input
+string, your program should produce a decimal output. The
+program should handle invalid inputs.
+
+## Note
+- Implement the conversion yourself.
+  Do not use something else to perform the conversion for you.
+
+## About Binary (Base-2)
+Decimal is a base-10 system.
+
+A number 23 in base 10 notation can be understood
+as a linear combination of powers of 10:
+
+- The rightmost digit gets multiplied by 10^0 = 1
+- The next number gets multiplied by 10^1 = 10
+- ...
+- The *n*th number gets multiplied by 10^*(n-1)*.
+- All these values are summed.
+
+So: `23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10`
+
+Binary is similar, but uses powers of 2 rather than powers of 10.
+
+So: `101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10`.
+
+## Source
+
+All of Computer Science [http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-](http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-)
+
+## Submitting Incomplete Problems
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+

mips/binary/runner.mips

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+#
+# Test binary_convert with some examples
+#
+# s0 - num of tests left to run
+# s1 - address of input word
+# s2 - address of expected output word
+# s3 - char byte
+# s4 - output word
+#
+# binary_convert must:
+# - be named binary_convert and declared as global
+# - read input address of string from a0
+# - follow the convention of using the t0-9 registers for temporary storage
+# - (if it uses s0-7 then it is responsible for pushing existing values to the stack then popping them back off before returning)
+# - write integer result to v0
+
+.data
+
+# number of test cases
+n: .word 9
+# input values (null terminated) & expected output values (word sized ints)
+ins:  .asciiz "0", "1", "10", "11", "100", "1001", "11010", "10001101000", "000011111"
+outs: .word     0,   1,   2,     3,    4,       9,      26,          1128,          31
+
+failmsg: .asciiz "failed for test input: "
+okmsg: .asciiz "all tests passed"
+
+
+.text
+
+runner:
+        lw      $s0, n
+        la      $s1, ins
+        la      $s2, outs
+
+run_test:
+        move    $a0, $s1                # move address of input str to a0
+        jal     binary_convert          # 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
+
+scan:
+        addi    $s1, $s1, 1             # move input address on byte forward
+        lb      $s3, 0($s1)             # load byte
+        beq     $s3, $zero, done_scan   # if char null, break loop
+        j       scan                    # loop
+
+done_scan:
+        addi    $s1, $s1, 1             # move input address on byte past null
+
+        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
+
+exit_ok:
+        la      $a0, okmsg              # put address of okmsg into a0
+        li      $v0, 4                  # 4 is print string
+        syscall
+
+        li      $v0, 10                 # 10 is exit with zero status (clean exit)
+        syscall
+
+exit_fail:
+        la      $a0, failmsg            # put address of failmsg into a0
+        li      $v0, 4                  # 4 is print string
+        syscall
+
+        move    $a0, $s1                # print input that failed on
+        li      $v0, 4
+        syscall
+
+        li      $a0, 1                  # set error code to 1
+        li      $v0, 17                 # 17 is exit with error
+        syscall
+
+# # Include your implementation here if you wish to run this from the MARS GUI.
+# .include "impl.mips"