Shrink Entity Struct

[caibear]

For the possibility of performance we can shrink the world.Entity struct to 32 bytes from 64 bytes (1/2 the size and still power of 2).
The point of this issue is to discuss if we should implement this to test it or if the cons would outweigh any estimated pros.

// The current struct (64 bytes):
type Entity struct {
	Transform                // 16 bytes (8 bytes pos + 4 bytes vel + 4 bytes dir)
	Guidance                 // 8 bytes (4 bytes vel + 4 bytes dir)
	EntityType               // 1 byte (eventually may be 2 bytes once entity count > 255)
	Damage   float32         // 4 bytes
	Distance float32         // 4 bytes
	Lifespan float32         // 4 bytes
	Owner    *Player         // 8 bytes
	ext      unsafeExtension // 8 bytes
        // EntityID EntityID     // 4 bytes
        // _ [4]byte             // 4 bytes struct padding
}

Required changes:

• Convert world.Angle from float32 to uint16 with 0 meaning 0.0 and 65535 being 2 Pi * 65535 / 65536.
• Move world.Extension (unsafeExtension) to world.Player.
• Move Entity.Damage to world.Extension.
• Remove Entity.Distance as it can be estimated from lifespan.
• Change lifespan and velocity(Target) to uint16 and int16 (Lifespan measured in 100/ms increments).

// The new struct (32 bytes):
type Entity struct {
	Transform                // 12 bytes (8 bytes pos + 2 bytes vel + 2 bytes dir)
	Guidance                 // 4 bytes (2 bytes vel + 2 bytes dir)
        Owner    *Player         // 8 bytes
	EntityType               // 1 byte (eventually may be 2 bytes once entity count > 255)
	Lifespan uint16          // 2 bytes
        // EntityID EntityID     // 4 bytes
}

Possible Pros:

• Entities use 1/2 the memory.
• Better locality of reference for iterating entities (speculating ~5-10% performance improvement of world functions from previous optimization).
  *Angles can be added/subtracted together without expensive math32.Mod.
• Allows us to do further optimizations with less copying like AOS vs SOA.

Cons:

• Player can't have more than 1 boat in the future (unless we make []Extension).
• More complex math and marshaling for angles, velocities, and lifespans.
• Entity.Distance() is just an estimate and may not be accurate.
• If we want to add more fields we will need to be more creative in the future.

Note that this is just an idea and may not be worth the added complexity.

[finnbear]

How can the difference between two angles be calculated if negative angles cannot be represented?

[caibear]

You can just convert the angle to an int16 when you want to have that representation.

[caibear]

Angle has been converted to uint16 completing one of the requirements.

[caibear]

Velocity has been converted to int16 completing another one of the requirements.

[caibear]

Entity.Distance has been removed completing another one of the requirements.

[caibear]

Once #69 is merged lifespan will be uint16. There are only 2 more requirements left.

[caibear]

Damage has been moved.

[caibear]

Moved extension to Player.

[caibear]

Benchmark Comparison on my computer:

benchmark                                         old ns/op     new ns/op     delta
BenchmarkSectorWorld/EntityByID/64-12             219           225           +2.69%
BenchmarkSectorWorld/EntityByID/256-12            221           225           +1.76%
BenchmarkSectorWorld/EntityByID/1024-12           234           231           -1.41%
BenchmarkSectorWorld/EntityByID/4096-12           269           256           -4.90%
BenchmarkSectorWorld/EntityByID/16384-12          297           288           -2.86%
BenchmarkSectorWorld/EntityByID/65536-12          346           331           -4.20%
BenchmarkSectorWorld/InRadius/64-12               224           220           -1.52%
BenchmarkSectorWorld/InRadius/256-12              251           249           -0.80%
BenchmarkSectorWorld/InRadius/1024-12             351           342           -2.40%
BenchmarkSectorWorld/InRadius/4096-12             356           352           -1.10%
BenchmarkSectorWorld/InRadius/16384-12            371           360           -2.83%
BenchmarkSectorWorld/InRadius/65536-12            371           367           -1.08%
BenchmarkSectorWorld/Iterate/64-12                28.0          27.5          -1.93%
BenchmarkSectorWorld/Iterate/256-12               26.4          25.5          -3.52%
BenchmarkSectorWorld/Iterate/1024-12              26.1          26.2          +0.38%
BenchmarkSectorWorld/Iterate/4096-12              27.6          25.4          -8.11%
BenchmarkSectorWorld/Iterate/16384-12             27.1          26.5          -2.40%
BenchmarkSectorWorld/Iterate/65536-12             28.8          27.6          -3.86%
BenchmarkSectorWorld/IterateParallel/64-12        165           165           -0.06%
BenchmarkSectorWorld/IterateParallel/256-12       55.4          53.4          -3.56%
BenchmarkSectorWorld/IterateParallel/1024-12      23.3          22.3          -4.33%
BenchmarkSectorWorld/IterateParallel/4096-12      11.5          10.7          -6.86%
BenchmarkSectorWorld/IterateParallel/16384-12     6.53          6.04          -7.47%
BenchmarkSectorWorld/IterateParallel/65536-12     4.72          4.37          -7.43%
BenchmarkSectorWorld/IterateRadius/64-12          302           276           -8.70%
BenchmarkSectorWorld/IterateRadius/256-12         341           305           -10.53%
BenchmarkSectorWorld/IterateRadius/1024-12        439           417           -4.99%
BenchmarkSectorWorld/IterateRadius/4096-12        441           418           -5.19%
BenchmarkSectorWorld/IterateRadius/16384-12       454           431           -5.15%
BenchmarkSectorWorld/IterateRadius/65536-12       460           436           -5.35%

[finnbear]

benchmark                                        old ns/op     new ns/op     delta
BenchmarkSectorWorld/EntityByID/64-8             57.9          55.9          -3.56%
BenchmarkSectorWorld/EntityByID/256-8            66.1          55.3          -16.41%
BenchmarkSectorWorld/EntityByID/1024-8           59.4          56.9          -4.36%
BenchmarkSectorWorld/EntityByID/4096-8           65.0          62.4          -4.09%
BenchmarkSectorWorld/EntityByID/16384-8          73.3          71.1          -3.02%
BenchmarkSectorWorld/EntityByID/65536-8          120           90.2          -25.18%
BenchmarkSectorWorld/InRadius/64-8               57.8          58.2          +0.76%
BenchmarkSectorWorld/InRadius/256-8              66.4          66.1          -0.35%
BenchmarkSectorWorld/InRadius/1024-8             90.0          91.2          +1.27%
BenchmarkSectorWorld/InRadius/4096-8             93.3          94.3          +1.09%
BenchmarkSectorWorld/InRadius/16384-8            95.7          98.1          +2.50%
BenchmarkSectorWorld/InRadius/65536-8            99.9          100           +0.09%
BenchmarkSectorWorld/Iterate/64-8                6.99          6.82          -2.43%
BenchmarkSectorWorld/Iterate/256-8               6.59          6.31          -4.25%
BenchmarkSectorWorld/Iterate/1024-8              6.69          6.26          -6.34%
BenchmarkSectorWorld/Iterate/4096-8              6.73          6.68          -0.70%
BenchmarkSectorWorld/Iterate/16384-8             6.80          6.62          -2.69%
BenchmarkSectorWorld/Iterate/65536-8             8.67          6.95          -19.87%
BenchmarkSectorWorld/IterateParallel/64-8        27.0          27.1          +0.52%
BenchmarkSectorWorld/IterateParallel/256-8       10.5          10.0          -5.03%
BenchmarkSectorWorld/IterateParallel/1024-8      5.97          5.49          -8.08%
BenchmarkSectorWorld/IterateParallel/4096-8      3.89          3.58          -7.89%
BenchmarkSectorWorld/IterateParallel/16384-8     2.21          2.09          -5.57%
BenchmarkSectorWorld/IterateParallel/65536-8     2.04          1.53          -25.13%
BenchmarkSectorWorld/IterateRadius/64-8          77.8          70.0          -10.05%
BenchmarkSectorWorld/IterateRadius/256-8         82.5          78.0          -5.45%
BenchmarkSectorWorld/IterateRadius/1024-8        115           111           -3.65%
BenchmarkSectorWorld/IterateRadius/4096-8        118           112           -5.26%
BenchmarkSectorWorld/IterateRadius/16384-8       122           115           -5.67%
BenchmarkSectorWorld/IterateRadius/65536-8       125           118           -5.77%