(Free42) accuracy of LN1+X

[ijabbott]

(06-12-2020 08:21 PM)grsbanks Wrote:  

(06-12-2020 06:51 PM)Albert Chan Wrote:  Perhaps it is implemented with binary128 version log1p ?

Looks like it is.

Code:

Phloat log1p(Phloat p) {
    BID_UINT128 res;
    bid128_log1p(&res, &p.val);
    return Phloat(res);
}

That code snippet by itself says nothing about the implementation of bid128_log1p, although looking at the source for the function itself (e.g. this copy on GitHub), most cases are wrapped around calls to bid128_to_binary128 and binary128_to_bid128 with the real work done in binary.