# Simple Bitmap
Simple bitmap is to provide very basic functionality for a bitmap, which allows to set arbitrary bits (within system limit), check the membership and get the index of the MSB (most significant bit).
## Usage
Below code illustrates typical use cases for the simple bitmap:
```elixir
iex> b = SimpleBitmap.new()
%SimpleBitmap{data: 0}
iex> b = SimpleBitmap.set(b, 5)
%SimpleBitmap{data: 32}
iex> b = SimpleBitmap.set(b, 10)
%SimpleBitmap{data: 1056}
iex> b = SimpleBitmap.set(b, 38)
%SimpleBitmap{data: 274877908000}
iex> b = SimpleBitmap.set(b, 179)
%SimpleBitmap{data: 766247770432944429179173513575154591809369835969709088}
iex> SimpleBitmap.msb(b)
179
iex> SimpleBitmap.msb(b, 10)
[179, 38, 10, 5, 0, 0, 0, 0, 0, 0]
```
If you'd know more, just look into the test cases and the source code itself. After all, the whole code is just < 200 LOC.
## Performance
We use [benchee](https://github.com/PragTob/benchee) to do the performance benchmark. The bitmap size is 1M bits. Here's the result for 1.0.0:
```bash
$ make bench
Benchmark the simple bitmap...
Operating System: macOS
CPU Information: Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
Number of Available Cores: 8
Available memory: 16 GB
Elixir 1.8.1
Erlang 21.2.4
Benchmark suite executing with the following configuration:
warmup: 1 s
time: 5 s
memory time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 30 s
Benchmarking get msb list...
Benchmarking load bitmap...
Benchmarking save bitmap...
Benchmarking set random bits...
Benchmarking unset random bits...
Generated benchmarks/output/bitmap.html
Generated benchmarks/output/bitmap_comparison.html
Generated benchmarks/output/bitmap_get_msb_list.html
Generated benchmarks/output/bitmap_load_bitmap.html
Generated benchmarks/output/bitmap_save_bitmap.html
Generated benchmarks/output/bitmap_set_random_bits.html
Generated benchmarks/output/bitmap_unset_random_bits.html
Opened report using open
Name ips average deviation median 99th %
set random bits 88.68 K 11.28 μs ±196.30% 9 μs 38 μs
unset random bits 44.62 K 22.41 μs ±176.87% 21 μs 60 μs
load bitmap 2.86 K 349.06 μs ±17.69% 327 μs 553 μs
save bitmap 1.05 K 950.09 μs ±29.21% 872 μs 1765.44 μs
get msb list 0.72 K 1391.21 μs ±10.05% 1365 μs 1859.88 μs
Comparison:
set random bits 88.68 K
unset random bits 44.62 K - 1.99x slower
load bitmap 2.86 K - 30.95x slower
save bitmap 1.05 K - 84.25x slower
get msb list 0.72 K - 123.37x slower
Suite saved in external term format at benchmarks/benchee/bitmap.benchee
Operating System: macOS
CPU Information: Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
Number of Available Cores: 8
Available memory: 16 GB
Elixir 1.8.1
Erlang 21.2.4
Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 0 ns
Name ips average deviation median 99th %
set random bits (1.0.0) 88.68 K 11.28 μs ±196.30% 9 μs 38 μs
unset random bits (1.0.0) 44.62 K 22.41 μs ±176.87% 21 μs 60 μs
load bitmap (1.0.0) 2.86 K 349.06 μs ±17.69% 327 μs 553 μs
save bitmap (1.0.0) 1.05 K 950.09 μs ±29.21% 872 μs 1765.44 μs
get msb list (1.0.0) 0.72 K 1391.21 μs ±10.05% 1365 μs 1859.88 μs
Comparison:
set random bits (1.0.0) 88.68 K
unset random bits (1.0.0) 44.62 K - 1.99x slower
load bitmap (1.0.0) 2.86 K - 30.95x slower
save bitmap (1.0.0) 1.05 K - 84.25x slower
get msb list (1.0.0) 0.72 K - 123.37x slower
```
Benchmark code is in [benchmarks/bitmap.exs](./benchmarks/bitmap.exs).
## Installation
The package can be installed by adding `simple_bitmap` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:simple_bitmap, "~> 1.0.0"}
]
end
```
