Things Found Under Lifted or Destroyed Objects
(Bushes, Grass squares, Rocks, Rock Piles, Pots, Signs, and Big Square Blocks)
Mini Algorithm Guide
Version 1.0
by Assassin
21 August 2013 (and some mysterious earlier date, if the Deja Vu is believed)

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Upon lifting, slicing down, or bombing a bush (which can be green, purple, or
brownish green), lifting a rock (which can be small or large, light or dark,
normal or skull), lifting a pot (which can be brown or a skull), lifting a sign
(which can be brown or yellow), slicing or bombing a square of grass, dashing
into a rock pile, or lifting a large, gray, square block, the game performs the
following steps to determine what will be found under it:

1) If there is a nonzero item ID assigned to the lifted/destroyed object, skip
   to Step 5.

2) If we're indoors, skip to Step 5.

3) If what we're looking under isn't grass or a normal green (not brownish
   green) or purple bush, skip to Step 5.

4) This step will "randomly" choose an item ID for what's under a bush or
   square of grass, as there was no specific entity assigned to it (or Item ID
   00h - Nothing was literally assigned to it).  It has several substeps:

   A. Randomly skip to Step 5 one half of the time.
   B. If there are four or more non-Link sprites/monsters onscreen (not
      counting Sprite 6Ch, whatever that is), skip to Step 5 to avoid
      overcrowding.
   C. If we're not in at least Phase 2 of the game (i.e. we haven't brought
      Princess Zelda to the Sanctuary yet), then skip to Step 5.
   D. Get our current square of the map.  It'll be a 0-63 value, as the
      overworld maps are 8x8 grids.  Two notes:
      - Large map sections are 2x2, with one square number taking the place of
        4 positions.  For example, the Mysterious Woods / Skeleton Forest is
        all indexed with Position 0, rather than with 0, 1, 8, and 9.
      - The square number actually comes from the bottom 6 bits of a Screen
        Number variable, which holds 0 - 63 for normal Light World map screens,
        64 - 127 for normal Dark World map screens, and 128+ for special
        screens (e.g. the Master Sword screen, the camp under the bridge, and
        Zora's Lake).  The top two bits are ignored.  So the Zora area, for
        instance, is screen 129, but gets treated like it's Screen 1 (whose
        random prize/sprite data is a duplicate of Screen 0 - Mysterious
        Woods, and doesn't disable anything).  This oversight allows for a
        crazy, garbled looking foe to turn up, as Zora's Waterfall lacks the
        tile set to properly display the Green Soldier.
   E. Load our 0 to 7 bush/grass prize pack counter, which indexes two prize
      packs (one for each world) of eight entries each.  Increment it for our
      next use (wrapping to zero if it exceeds seven).  On the GBA version,
      it apparently loads the post-incremented value instead.
      (Note that this counter is reinitialized to 0 after a system reset or
      powerdown, even if you'd saved your game.  However, on the SNES version,
      it is retained after Saving, Quitting, and reloading (and you can even
      temporarily copy it between save slots by saving on one, then loading
      another).)
   F. The prize packs for each world are:

      Light World = 01h, 01h, 01h, 01h, 0Fh, 01h, 01h, 12h
        (Green Rupee, Green Rupee, Green Rupee, Green Rupee, Green Soldier
         with Sword, Green Rupee, Green Rupee, Ground Bomb / Land Mine)
      Dark World = 10h, 01h, 01h, 01h, 11h, 01h, 01h, 03h
        (Awakening Skull Rock, Green Rupee, Green Rupee, Green Rupee,
         Blue Helmeted Bull with Poker, Green Rupee, Green Rupee, Bee)

      Get the Item ID from the slot indexed by our loaded prize pack counter.
      However, instead proceed to Step 5 without loading an Item ID if both of
      these conditions are met:
      - Our intended prize pack slot is preventable in the current world (see
        list); that is, it has a nonzero prevention flag.
      - The current map square has this prevention flag present in its list of
        exclusions.  (Each square has a single list used for both worlds.)

      Preventable "random" sprites:
       Light World = Slot 4, Slot 7
                     (Green Soldier with Sword, Ground Bomb / Land Mine)
       Dark World = Slot 0, Slot 4
                   (Stal / Awakening Skull Rock, Blue Helmeted Bull with Poker)

5) If we're indoors, skip to Step 7.

6) Randomly exit and return nothing one half of the time.

7) If an ID of 00h (or nothing) was originally assigned to the bush/grass/rock/
   pot/rock pile/sign/block, and Step 4 did not change it by picking a new ID,
   exit and return nothing.

8) If an ID of 04h (Random) was originally assigned to the lifted/destroyed
   object, randomly pick an item ID ranging from 13h through 16h.  Otherwise,
   just stick with the assigned ID.

9) Convert the Item ID into a sprite using the table below.  If the sprite is
   00h (Nothing), then don't actually put that on the map (as it'd be a
   Crow/Raven or Kyune/Horned bird), but exit and don't return anything.

     Item ID   |  Sprite (ID)
  -------------+------------------------------------------------------
      01h      |   Green Rupee (D9h)
      02h      |   Rock Spider/Beetle/Crab/Hoarder (3Eh)
      03h      |   Bee (79h)
      04h      |   Random (special case - see Step 8)
               |    (Note that Green Rupee is in the data here, but
               |    it's just a placeholder.)
      05h      |   Bomb x 1 (DCh)
      06h      |   Heart (D8h)
      07h      |   Blue Rupee (DAh)
      08h      |   Key (E4h)
      09h      |   Arrow x 5 (E1h)
      0Ah      |   Bomb x 1 (DCh)
      0Bh      |   Heart (D8h)
      0Ch      |   Partial Magic refill (DFh)
      0Dh      |   Full Magic refill (E0h)
      0Eh      |   Cucco/Chicken [LW] or Cucco/Chicken skeleton [DW]
               |    (both 0Bh)
      0Fh      |   Green Soldier with Sword (42h)
      10h      |   Stal / Awakening Skull Rock (D3h)
      11h      |   Blue Soldier with Sword [LW] or Blue Helmeted Bull
               |    with Poker [DW] (both 41h)
      12h      |   Ground Bomb aka Land Mine (D4h)
      13h      |   Green Rupee (D9h)
      14h      |   Faerie/Fairy (E3h)
      15h      |   Heart (D8h)
      16h      |   Nothing (00h - special case, see above)

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 RECOMMENDED READING
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This document doesn't get into which prize pack slots are disabled by which
map squares.  To see that information, you'll want to consult the "Commented
code and data for item uncovering" on my website:

http://home.comcast.net/~assassin17/zelda3_guides.htm  OR
http://www14.brinkster.com/assassin17/zelda3_guides.htm

Compare the map data in the 1A/FB7B structure to the 1A/FBCB or 1A/FBD3
structure (depending on which world), and see when common bits are set.

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 CREDITS
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- Susan Carriere, for suggesting I create a more readable document to
  supplement the commented disassembly of the findings under bushes, grass,
  rocks, etc.  Then for providing various helpful feedback on the document:
  suggesting a preamble, pointing out a step omission which would have allowed
  keys under pots being randomly missable, asking for elaboration on
  preventable random prizes, clearing up ambiguity in Step 8, and suggesting I
  account for the different-sized rocks (which eventually led to me listing
  every relevant covering object).

- Lady_Birdo for pointing out that the glitched enemy at Zora's Waterfall was
  a soldier.  I couldn't tell what I was looking at.

- BaronDante for explaining that the glitched appearance stems from the
  soldier's tile set not being loaded in that area.

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 REVISION HISTORY
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Version 1.0: 2009 and maybe 2010; July 10-13 and 15, 2013; August 14-16, 18-19,
             and 21, 2013:

 - Released a commented disassembly on July 12, 2009, after starting work on
   it sometime before March 27, 2009.  But that wasn't necessarily readable by
   most humans.
 - Starting in August 2009 and maybe extending into early 2010, wrote a
   document that had about 90% of the step content you see here.  However, I
   never uploaded it anywhere, as it wasn't quite done, and the hard drive of
   the computer housing it crashed. :O  I couldn't stomach the idea of
   re-composing something I'd already done, and figured I'd retrieve it
   whenever the hard drive was restored.  (It's probably just a service sector
   issue.)  However, by mid 2013, still having yet to bring the disk anywhere,
   I had an epiphany that I am even cheaper than I am lazy.  So I decided to
   bite the bullet and remake the document.
 - July 10-13 and 15, 2013: Wrote document, then improved it based on Susan
   Carriere's suggestions.
 - August 14-16 and 18-19: Added "Stal" as a name for the skull rock enemy, and
   "Hoarder" and "Crab" for the Rock Beetle/Spider.  Added Credits and Revision
   History sections.  Added GBA and reset/reload info to Step 4E.
 - August 21, 2013: Released document.