how to use fift function in func? is there any useful link please?

for example II have a number generator in generator.fif named :generator which has one number as input and returns a hashed number
how I can call it in the my FunC method

Fift is executed during compilation, so you can't.

https://docs.ton.org/develop/fift/fift-and-tvm-assembly

If you're asking about private code, you can create some public example.

you right, sorry.
I want to translate it as asm to reduce gas usage of my FunC code
{ 0 1 rot { 2dup + } swap times } : generator

I understand that you're trying to solve task 5 😀
So I will mention only part of asm code: "REPEAT:<{ 2DUP ADD }>".

https://www.youtube.com/playlist?list=PLtUBO1QNEKwttRsAs9eacL2oCMOhWaOZs

(int, int) get_n(int n) asm "NIL OVER 0 EQINT 0 PUSHINT s0 s4 XCHG REPEAT:<{ s3 PUSH ADD s0 s3 }> NIP";
Error: main.fif:17: }>:not a cell builder
I just start learning asm
help me please to understand what's wrong with this code, Thank you

ADD s0 s3 does not mean anything.

ADD s0 s3 XCHG does?

how to return a stack from asm ?
(int, int) get_n(int n) asm "NIL OVER 0 PUSHINT 1 PUSHINT s0 s4 XCHG REPEAT:<{ s3 PUSH ADD s0 s3 XCHG }> NIP";
s2 is returning which is array. I used document sample codes so I can not fully understand
I'm trying to understand what's going on and why I have a tuple in my s0~s4 args

n:7 it's returns
#DEBUG#: s0 = []
#DEBUG#: s0 = 13
which should be
#DEBUG#: s0 = 21
#DEBUG#: s0 = 13

and the stacks dump is
#DEBUG#: s0 = 13
#DEBUG#: s1 = 7
#DEBUG#: s2 = []
#DEBUG#: s3 = 21
#DEBUG#: s4 = 1