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NAV
   
 * Introduction
 * Levels
     
   * Year 1 Mail Room
       
     * Solution
   * Year 2 Busy Mail Room
       
     * Optimized for Size
     * Loop Unroll for Speed
     * INBOX before JUMP for Speed
   * Year 3 Copy Floor
       
     * Solution
   * Year 4 Scrambler Handler
       
     * Solution
   * Year 6 Rainy Summer
       
     * Solution
     * Optimization
 * Optimization Techniques
     
   * Speed Optimization
       
     * Loop Unroll
     * INBOX before JUMP
 * Exceptional Circumstances
     
   * Ending Execution
   * Program Length
   * Infinite Loops

 * See also atesgoral’s solution collection
 * Open-source icons created by Ida Desi Mariana - Flaticon


INTRODUCTION

Human Resource Machine is a programming puzzle game by Tomorrow Corporation. It
teaches programming concepts and program flow, and includes optimization goals
for size and speed.

This walkthrough describes straightforward answers for select levels, then
explores the methods that can be used to reach the optimization goals.

There are two optimization goals for each level:

 * The size optimization goal seeks the smallest program that achieves the level
   goal.
 * The speed optimization goal seeks the program that achieves the level goal in
   the shortest time. Each command processed takes one time unit.

There is a section at the end summarizing the optimization techniques used.


LEVELS


YEAR 1 MAIL ROOM

Grab each thing from the INBOX and drop it into the OUTBOX.

 * 6 or fewer instructions.
 * 6 or fewer steps.

New instructions available:

 * INBOX: Get an item from the inbox.
 * OUTBOX: Put an item into the outbox, emptying our hands.


SOLUTION

    INBOX
    OUTBOX
    INBOX
    OUTBOX
    INBOX
    OUTBOX


> Copy three inbox items to the outbox.

There is the only one approach in the Mail Room, since we only have two
instructions available.

Since the test data has up to three inputs we just do three INBOX instructions
matched with three OUTBOX instructions.

The initial solution satisfies the optimization goals.


YEAR 2 BUSY MAIL ROOM

Grab each thing from the INBOX and drop it into the OUTBOX.

 * 3 or fewer instructions.
 * 25 or fewer steps.

We can either satisfy the size goal or the speed goal, but cannot satisfy both
at the same time (since speed optimisation requires more than three
instructions).

New instructions available:

 * JUMP: Jump to another location in the code.


OPTIMIZED FOR SIZE

a:
    INBOX
    OUTBOX
    JUMP   a


> Copy inbox items to the outbox. Size 3, 30 steps.

The smallest approach is to copy one item, then loop back to the start and copy
the next item. This costs 3 steps per item, for a total of 30 steps.


LOOP UNROLL FOR SPEED

a:
    INBOX
    OUTBOX
    INBOX
    OUTBOX
    JUMP   a


> Loop unrolled version. Size 5, 25 steps.

Loop unrolling is the process of copying the same block of instructions multiple
times to save one JUMP instruction per copy.

In this challenge the test data has up to 12 items. The most extreme loop unroll
would result in 12 INBOX instructions with 12 matching OUTBOX instructions,
giving a size of 24 and a worst time of 24 steps (average 20).


INBOX BEFORE JUMP FOR SPEED

    INBOX
a:
    OUTBOX
    INBOX
    OUTBOX
    INBOX
    JUMP   a


> Loop unrolled version with INBOX then JUMP optimisation. Size 6, 24 steps.

INBOX before JUMP is a technique of moving the INBOX instruction that would
occur after a JUMP instruction so that it occurs before that instruction. This
saves one step overall, because the program stops when INBOX sees an empty
inbox. Otherwise the final JUMP costs one step before INBOX ends the program.


YEAR 3 COPY FLOOR

Copy the letters “BUG” from the floor to the outbox.

 * 6 or fewer instructions.
 * 6 or fewer steps.

New instructions available:

 * COPYFROM: Read a value from a tile on the floor.


SOLUTION

    COPYFROM 4
    OUTBOX
    COPYFROM 0
    OUTBOX
    COPYFROM 3
    OUTBOX


> Copy the letters BUG from the floor to the outbox. Size 6, 6 steps.

Since the floor has 6 tiles with letters, and only three of them are suitable
for the goal, there is only one answer (unless you waste extra time on
operations that don’t affect the outbox).

The initial solution satisfies the optimization goals.


YEAR 4 SCRAMBLER HANDLER

For each two things in the inbox, swap their order and put them in the outbox.

 * 7 or fewer instructions.
 * 21 or fewer steps.

New instructions available:

 * COPYTO: Read a value from a tile on the floor.


SOLUTION

a:
    INBOX
    COPYTO   1
    INBOX
    OUTBOX
    COPYFROM 1
    OUTBOX
    JUMP     a


> Swap the order of each pair of input items. Size 7, 21 steps.

 1. Copies the first item from each pair to tile 1.
 2. Puts the next item from the inbox directly into the outbox.
 3. Finally read the first item from tile 1 and put it into the outbox.
 4. Jump back to the start to process more items.

The number of steps required could be reduced by unrolling the loop, however
that would increase the number of instructions past the goal.

The initial solution satisfies the optimization goals.


YEAR 6 RAINY SUMMER

For each two things in the inbox, add them and put the result in the outbox.

 * 6 or fewer instructions.
 * 24 or fewer steps.


SOLUTION

a:
    INBOX
    COPYTO   1
    INBOX
    ADD      1
    OUTBOX
    JUMP     a


> Add each pair of input items. Size 6, 24 steps.

 1. Copies the first item from each pair to tile 1.
 2. Gets the next item from the inbox and adds the first value (from tile 1).
 3. Puts the result into the outbox.
 4. Jump back to the start to process more items.

The initial solution satisfies the optimization goals.


OPTIMIZATION

The number of steps required could be reduced by unrolling the loop, however
that would increase the number of instructions past the goal.

INBOX before JUMP would reduce the overall steps required by one, at the cost of
one additional instruction.


OPTIMIZATION TECHNIQUES


SPEED OPTIMIZATION


LOOP UNROLL

    INBOX
    OUTBOX
    INBOX
    OUTBOX
    INBOX
    OUTBOX


> Three inbox to outbox commands, loop unrolled.

Loop unrolling removes one JUMP step per copied code block at the size cost of
the additional code block.


INBOX BEFORE JUMP

    INBOX
a:
    OUTBOX
    INBOX
    OUTBOX
    INBOX
    JUMP   a


> INBOX before JUMP saves one JUMP when inbox is empty.

INBOX before JUMP remove one JUMP step for the final input item. It may have a
size cost of one additional command depending on the program structure.


EXCEPTIONAL CIRCUMSTANCES


ENDING EXECUTION

There are two ways to end execution and check for completion of the goals:

 * INBOX when the inbox is empty.
 * Let execution run off the end of the program.

These actions end execution with an error:

 * OUTBOX with an unexpected value.
 * Attempting to use a value when you’re not holding one (e.g. after OUTBOX).


PROGRAM LENGTH

Programs can be up to 255 lines long. Both instructions and destinations for
JUMP instructions count as lines. Nothing bad happends once you reach 255 lines,
but you cannot add more instructions.


INFINITE LOOPS

Programs can run for a long time. Presumably you will eventually run out of
memory (for stepping backwards in the debugger).

code