Following Fast powi function topic, I made a fast-powi crate. I only implemented 8-bit exponents; i.e, i8 and u8. I don't know of any practical use of exponents greater than 127. This allowed me to hard-code all the shortest "addition-chains" (or multiplication-chains in this case) for all u8 exponents. I decided to implement the num crate numerical types. It is about 10X faster than the standard library powi for floats on my computer. It is about 20% faster than most ints, bigints, and ratios. It is about 50% faster for complex ratio types.

Here is a summary of the benchmarks from my laptop.

f64_fast                time:   [765.08 ns 772.03 ns 778.96 ns]
f64_std                 time:   [8.1878 µs 8.2823 µs 8.3878 µs]

bigint_fast             time:   [70.852 µs 71.336 µs 71.814 µs]
bigint_num              time:   [89.324 µs 89.779 µs 90.293 µs]

big_ratio_fast          time:   [303.19 µs 304.39 µs 305.70 µs]
big_ratio_num           time:   [355.01 µs 357.22 µs 359.59 µs]

u64_fast                time:   [105.52 ns 107.19 ns 108.99 ns]
u64_num                 time:   [210.32 ns 213.48 ns 218.01 ns]

big_complex_ratio_fast  time:   [23.048 ms 23.522 ms 24.193 ms]
big_complex_ratio_num   time:   [32.578 ms 32.965 ms 33.449 ms]

You can find the benchmark code here

I probably should have ask for a review before publishing on crate.io, but I got "go fever" to publish my first crate. I would appreciate any input.

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