# Regeneration

In StarCraft, regeneration is the slow increase of a unit's health, shields, or energy.

### How It Works

To understand regeneration, you have to understand that Starcraft hides data from you. Health and Shields each are stored in memory in 4 bytes, however Starcraft only tells you the last 3 bytes. The first byte is actually a hidden value which acts as a timer for regeneration. 1 byte = 8 bits, or 2^{8} = 256.

Each frame, a certain regeneration amount is added (or subtracted) to the first byte, according to values in the mpqs:

- Protoss Shields: 7
- Zerg Health: 4
- Energy: 8
- Shield Battery: 1280
- Recharge Shields: -640 (-632 net)
- Burning Terran Building: -20
- Medic: 200
- Personnel Cloaking(Ghost): -18 (-10 net)
- Cloaking Field(Wraith): -21 (-13 net)
- Heal: -100 (-92 net)

SCVs repair units and buildings in a similar way, based on build time and total HP. Multiple SCVs increase the repair rate by adding them together.

R = roundup(.9 * H/B)

where R = repair rate in 1/256 of hp per frame, H = HP, B = build rate in SCMDraft.

One important note is that R is a 2 byte value, which means that when R > 65535, it loops back over to 0. Here is an example:

A Terran Barracks with a build time of 1, HP of 9999.

R = roundup(.9 * 256*9999/1) = 2303770. R>65535, so it rolls over in multiples of 65535.

R = 2303770- k65535, R = 10010. Note that this is still fairly large, and means that each SCV will repair approximately 39 HP every frame.

A slightly more realistic value is that of the default battlecruiser with 500 HP, 2000 Build time:

R= roundup(.9 * 500*256/2000) = 58.

Building units follows the same formula, and this explains why some buildings/units come out injured, except they start out with 10% of the base HP, plus 1 frame of "repairing", plus the time it takes to build. In the case of the terran barracks, it will build in 1 frame and come out with .1 * 9999 + 10010/256 + 10010/256 = 1078.1 HP.

### Healing Rates

*The time used here is realtime.*
Since Starcraft is normally played on fastest, or 42ms/frame, we can calculate the approximate rates of healing:

- Let sp = shield points, hp = hit points, f = frames, ms = milliseconds, s = seconds, p = fraction of points
- Protoss shields use 7, (256p/sp / 7p/f) / (1000ms/s / 42ms/f) = 1.536 seconds per shield point.
- Zerg Health use 4, so (256/4)/(1000/42) = 2.688 seconds per health point.
- Medics' Healing uses 200, so (256/200)/(1000/42) = 0.05376 seconds per health point or ~18.6 health per second.
- Shield batteries use 1280, so 256/1280/24 = 0.0084 seconds per shield point or ~119 shields per second.

Other rates can be similarly calculated.