Implement exp/pow function

[lmatz]

https://www.postgresql.org/docs/7.4/functions-math.html:

Function                  | Return Type
exp(dp or numeric)        | (same as input)
pow(a dp, b dp)           | dp
pow(a numeric, b numeric) | numeric

• pow(a numeric, b numeric) | numeric: fix(expr): pow behavior for decimal and special values #10028
• pow(a dp, b dp) | dp: feat(expr): support pow function #7789
• exp(dp) | dp: feat: support exp and refactor pow #7971
• exp(numeric) | numeric: feat(expr): support unary trunc, ln, log10 (log), exp, cbrt (||/) #9991

[lmatz]

maybe exclude Decimal/Numeric first

[snipekill]

Hey Imatz, I wanted to contribute to the project, can you help me point out right resources and code pointers for implementing this.

[lmatz]

Hey Imatz, I wanted to contribute to the project, can you help me point out right resources and code pointers for implementing this.

Hi @snipekill , thanks for your interest in this feature!
But since it is urgent, I am just going to implement it. Are you interested in some other issues? We are happy to help 😃

[lmatz]

          If we cast them in frontend, I guess we can only support a concrete implementation (f64,f64)->f64 instead of a general one.

Originally posted by @TennyZhuang in #7789 (comment)

[neverchanje]

Any updates for exp()?

[lmatz]

Decimal unsupported yet, only double precision.

After choosing a new Decimal crate.