Marine rate of fire

	int get_modified_weapon_cooldown(const unit_t* u, const weapon_type_t* weapon) const {
		int cooldown = weapon->cooldown;
		if (u->acid_spore_count) {
			cooldown += std::max(cooldown / 8, 3) * u->acid_spore_count;
		}
		int mod = 0;
	(1)	if (u->stim_timer) ++mod;
	(1)	if (u_cooldown_upgrade(u)) ++mod;
	(1)	if (u->ensnare_timer) --mod;
	(2)	if (mod > 0) cooldown /= 2;
	(3)	if (mod < 0) cooldown += cooldown / 4;
		if (cooldown > 250) cooldown = 250;
	(4)	if (cooldown < 5) cooldown = 5;
		return cooldown;
	}

• This means that Ensnare directly counteracts the effects of Stim Packs and Adrenal Glands.
  

• Marines have a base cooldown 15, that makes it 7 when stimmed.
  
• For Firebats, base cooldown is 22, so that gets reduced to 11 when stimmed.
  
• For Zerglings, base cooldown 8, that makes it 4
  (reference list for weapon cooldowns: https://bwapi.github.io/namespace_b_w_a_p_i_1_1_weapon_types.html#ad885bcaa092286d10a80133abcfbbfe1)
  

• This means Cracklings have an actual base cooldown of 5.
  

void attack_unit_fire_weapon(unit_t* u) {
		st.prev_bullet_source_unit = nullptr;
		if (u_cannot_attack(u)) return;
		unit_t* target = u->order_target.unit;
		const weapon_type_t* weapon;
		int cooldown;
		int anim;
		if (target && u_flying(target)) {
			weapon = unit_air_weapon(u);
			cooldown = u->air_weapon_cooldown;
			anim = iscript_anims::AirAttkRpt;
		} else {
			weapon = unit_ground_weapon(u);
			cooldown = u->ground_weapon_cooldown;
			anim = iscript_anims::GndAttkRpt;
		}
		if (!weapon) return;
		if (cooldown != 0) {
	(5)		if (u->order_process_timer > cooldown - 1) u->order_process_timer = cooldown - 1;
			return;
		}
		if (!unit_can_fire_weapon(u, weapon)) return;
		u_set_movement_flag(u, 8);
	(6)	cooldown = get_modified_weapon_cooldown(u, weapon) + (lcg_rand(12) & 3) - 1;
		u->ground_weapon_cooldown = cooldown;
		u->air_weapon_cooldown = cooldown;
		sprite_run_anim(u->sprite, anim);
	}

• For stimmed Marines, that means they have a cooldown between 6 and 9 frames, which in any case gets superseded by the order process timer.
  
• For stimmed Firebats the cooldown lies between 10 and 13 frames. At the 9th frame of the cooldown the order process timer gets reset to match the cooldown.
  
• Zerglings are a special case. They are the only unit in the game which can and does exceed the 9 frame cooldown threshold, due to its own exception in the code that synchronizes its attack cooldown and order process timer every frame (https://github.com/OpenBW/openbw/blob/master/bwgame.h#L1221):
  

  		if (unit_is(u, UnitTypes::Zerg_Zergling) || unit_is(u, UnitTypes::Hero_Devouring_One)) {
  			if (u->ground_weapon_cooldown == 0) u->order_process_timer = 0;
  		}

  
  

• This is how the Marine's attack iscript looks like:
  

  MarineGndAttkInit:
  	playfram       	0x00	# frame set 0
  	wait           	1
  	playfram       	0x11	# frame set 1
  	wait           	1
  	playfram       	0x22	# frame set 2
  MarineGndAttkRpt:
  	wait           	1
  	nobrkcodestart 	
  	playsnd        	69	# Bullet\TMaFir00.wav
  	attackwith     	1
  	playfram       	0x33	# frame set 3
  	wait           	1
  	playfram       	0x22	# frame set 2
  	wait           	1
  	playfram       	0x33	# frame set 3
  	wait           	1
  	playfram       	0x22	# frame set 2
  	wait           	1
  	playfram       	0x33	# frame set 3
  	wait           	1
  	playfram       	0x22	# frame set 2
  	wait           	1
  	nobrkcodeend   	
  	gotorepeatattk 	
  	ignorerest     	
  MarineGndAttkToIdle:
  	playfram       	0x11	# frame set 1
  	wait           	1
  	playfram       	0x00	# frame set 0
  	wait           	1
  	goto           	MarineWalkingToIdle

  
  We can determine the frame duration by simply summing up the the "wait" durations in each part, so there is a 2 frame attack initiation animation, then a repeating attack part of 8 frames, and a 2 frame back-to-idle animation.
  However, when processing iscripts, the game engine actually uses up two animation frames in the first game frame of the animation, so effectively animations are 1 frame shorter than their iscript suggests.
  This means a Marine's first attack on a target takes 2+8-1 = 9 frames to finish, any following repeating attack takes 7 frames.
  
  
• For the Firebat we get:
  

  FirebatGndAttkInit:
  	playfram       	0x00	# frame set 0
  FirebatGndAttkRpt:
  	wait           	1
  	nobrkcodestart 	
  	imgol          	421 0 0	# FlameThrower (thingy\flamer.grp)
  	playfram       	0x11	# frame set 1
  	attkshiftproj  	24
  	wait           	1
  	attkshiftproj  	52
  	wait           	1
  	attkshiftproj  	80
  	wait           	5
  	playfram       	0x00	# frame set 0
  	wait           	2
  	ignorerest     	
  FirebatGndAttkToIdle:
  	goto           	FirebatWalkingToIdle
  

  
  So there is no initiation animation in this case, and each attack repeat animation lasts for a total of 10-1 = 9 frames.
  
  
• The Zergling does not have any additional initiation frames, so every attack has an animation duration of 5-1 = 4 frames:
  

  ZerglingGndAttkInit:
      playfram           0x00    # frame set 0
      wait               1
      nobrkcodestart     
      playfram           0x11    # frame set 1
      wait               1
      playfram           0x22    # frame set 2
      attackmelee        1 894    # Zerg\Ultra\zulHit00.WAV
      wait               1
      playfram           0x33    # frame set 3
      wait               1
      playfram           0x44    # frame set 4
      wait               1
      nobrkcodeend       
      gotorepeatattk     
      goto               ZerglingGndAttkToIdle 

  
  

• Its attack cooldown timer must be 0.
  
• Its order process timer must be 0.
  
• Its previous animation (in case of a repeat attack, that is its previous attack animation) must be finished.
  If the order process timer hits 0 and the unit is still in an active animation, the next attack cannot be executed and instead the order process timer will be reset to enter its next 9 frame cycle.
  

UNIT_TYPE          BASE_CD  MIN_CD  MAX_CD  AVG_CD  INIT_ANIMATION  REPEAT_ANIMATION
Marine             15       14      17      15.5    9               7
Marine (stimmed)    7        6*      9       7.5*   9               7
Firebat            22       21      24      22.5    9               9
Firebat (stimmed)  11       10      13      11.5    9               9
Zergling            8        7      10       8.5    4               4
Crackling           5        4       7       5.5    4               4

*less than 9-frame order process timer cycle!

• For Marines, we get an average cooldown of 15.5 frames. However, when stimmed, the possible cooldowns 6,7,8,9 drop below the duration of the 9 frame order process timer cycle, so after each attack the game actually waits for the next reset of that cycle to initialize the next attack, making the effective cooldown 9.
  This gives us an attack rate (and hence DPS) increase of 15.5/9 - 1 = 72.22…%
  
• For Firebats we get an effective DPS increase of 22.5/11.5 - 1 = 95.65…%
  
• For Cracklings the DPS increase is 8.5/5.5 - 1 = 54.5454…%
  

• One can easily observe that Marines under the effect of Stim have uniform cooldowns of 9 frames by attacking a high HP target. All Marines will fire at it in perfect unison.
  
• The effect of an attack animation exceeding the duration of the unit's cooldown can best be observed with the Ultralisk, which has a base attack cooldown of 15 frames, exactly the same as its attack animation. This means that its cooldown rolls of {14, 15, 16, 17}, with a theoretical average of 15.5, will effectively be executed as {23, 15, 16, 17}, with an average of 17.75.
  This is the reason behind the irregular attack pattern one can observe with this unit, with a noticeable pause every 4 attacks, on average.
  This also explains why Ultralisk DPS is virtually unaffected by the effect of Ensnare. Ensnare increases the Ultralisk's base cooldown to 15 + ⌊15/4⌋ = 15+3 = 18, making {17,18,19,20} the possible cooldown rolls, with an average of 18.5, only slightly more than an unaffected Ultra.
  
• Another irregularity can be observed with Corsairs, which have a theoretical base cooldown of 8, less than the order process cycle, turning their theoretical {7, 8, 9, 10} rolls into effective cooldowns of {9, 9, 9, 10}, thus reducing their DPS by some 8% compared to what the unit stat suggests, as well as effectively lessening the effect Ensnare has, as it sets the base cooldown to 10, thus only causing a 1 - 9.25/10.5 = 11.90…% DPS reduction, as opposed to the nominal 20%.