[decimal] Optimize number_of_digit + improve the performance of multiply and exp (#31)

This pull request includes several changes across different files to
optimize the performance of `multiply` and `exp` and improve the
functionality and readability of the codebase. The changes involve
importing and utilizing new modules, refactoring functions for better
clarity, and fixing minor issues.

This PR significantly improve the speed when multiplying two decimals
with many digits after the decimal points (>20). This indirectly
enhances the performance of `exp` significantly.

### Utility Functions:
* Refactored the `truncate_to_max` function to use `power_of_10` for
calculating powers of ten.
* Optimize `number_of_digit` by using direct lookup instead of
calculating ad hoc.

### Arithmetic Functions:
* Refactored the `add` and `multiply` functions for better readability
and efficiency. This includes using `Decimal.from_uint128` for creating
`Decimal` objects and improving the handling of scale and rounding.

Author: forfudan

.github/workflows/run_tests.yaml

@@ -13,8 +13,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: ["macos-latest"]
-        # os: ["ubuntu-22.04"]
+        # os: ["macos-latest"]
+        os: ["ubuntu-22.04"]
 
     runs-on: ${{ matrix.os }}
     timeout-minutes: 30

benches/bench.mojo

@@ -6,6 +6,7 @@ from bench_sqrt import main as bench_sqrt
 from bench_from_float import main as bench_from_float
 from bench_from_string import main as bench_from_string
 from bench_comparison import main as bench_comparison
+from bench_exp import main as bench_exp
 
 
 fn main() raises:
@@ -17,3 +18,4 @@ fn main() raises:
     bench_from_float()
     bench_from_string()
     bench_comparison()
+    bench_exp()

benches/bench_exp.mojo

@@ -71,7 +71,7 @@ fn run_benchmark(
     var mojo_decimal = Decimal(input_value)
     var pydecimal = Python.import_module("decimal")
     var py_decimal = pydecimal.Decimal(input_value)
-    var py_math = Python.import_module("math")
+    var _py_math = Python.import_module("math")
 
     # Execute the operations once to verify correctness
     var mojo_result = dm.exponential.exp(mojo_decimal)

mojoproject.toml

@@ -33,7 +33,7 @@ debug_sqrt = "magic run package && magic run mojo tests/test_sqrt.mojo && magic
 test = "magic run package && magic run mojo test tests && magic run delete_package"
 t = "clear && magic run test"
 test_arith = "magic run package && magic run mojo test tests/test_arithmetics.mojo && magic run delete_package"
-test_div = "magic run package && magic run mojo test tests/test_division.mojo && magic run delete_package"
+test_divide = "magic run package && magic run mojo test tests/test_division.mojo && magic run delete_package"
 test_sqrt = "magic run package && magic run mojo test tests/test_sqrt.mojo && magic run delete_package"
 test_round = "magic run package && magic run mojo test tests/test_round.mojo && magic run delete_package"
 test_creation = "magic run package && magic run mojo test tests/test_creation.mojo && magic run delete_package"
@@ -46,8 +46,8 @@ test_exp = "magic run package && magic run mojo test tests/test_exp.mojo && magi
 # benches
 bench = "magic run package && cd benches && magic run mojo bench.mojo && cd .. && magic run delete_package"
 b = "clear && magic run bench"
-bench_mul = "magic run package && cd benches && magic run mojo bench_multiply.mojo && cd .. && magic run delete_package"
-bench_div = "magic run package && cd benches && magic run mojo bench_divide.mojo && cd .. && magic run delete_package"
+bench_multiply = "magic run package && cd benches && magic run mojo bench_multiply.mojo && cd .. && magic run delete_package"
+bench_divide = "magic run package && cd benches && magic run mojo bench_divide.mojo && cd .. && magic run delete_package"
 bench_sqrt = "magic run package && cd benches && magic run mojo bench_sqrt.mojo && cd .. && magic run delete_package"
 bench_round = "magic run package && cd benches && magic run mojo bench_round.mojo && cd .. && magic run delete_package"
 bench_from_float = "magic run package && cd benches && magic run mojo bench_from_float.mojo && cd .. && magic run delete_package"