You can multiply with short integers, saving MP_Set calls. This could be the shortest code:
Code:
factorial(n) {
MP_Set(result, 1)
Loop %n%
MP_MulIpp(tmpVal, result, A_Index)
,MP_Cpy(result, tmpVal)
Return MP_Dec(result)
}
You can also avoid copying long integers with a little longer function, which is, therefore, a little faster:
Code:
factorial(n) { ; n >= 0
If n < 4
Return SubStr("1261",n,1)
MP_Set(x,n), i := n
Loop % n//2-2
MP_MulIpp(y,x,--i)
,MP_MulIpp(x,y,--i)
MP_MulIpp(y, x, i=4 ? 6 : 24)
Return MP_Dec(y)
}
You can handle more than just the 4 possible smallest inputs directly. E.g. if the factorials of n<10 are directly returned, the loop can finish sooner and the last MP_MulIpp can have choices between 9! or 10!, resulting in further little speedups.
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