Does log need to be computed using floating-point representation?
This excludes the larger part of bignums.
This is a test:
(define x (expt 10 2480))
(log x)If the implementation wants to answer (log x) with the correct
number, the logarithm must be calculated without the floating-point
C library log function, since the number is far too large to fit
in current days 64-bit doubles.
| System | result |
|---|---|
| Bigloo | -inf.0 |
| Biwa | +inf.0 |
| Chez | 5710.411030625233 |
| Chibi | +inf.0 |
| Chicken | +inf.0 |
| Cyclone | +inf.0 |
| Foment | +inf.0 |
| Gambit | 5710.411030625233 |
| Gauche | 5710.411030625233 |
| Guile | 5710.411030625233 |
| Kawa | +inf.0 |
| LIPS | +inf.0 |
| Loko | +inf.0 |
| MIT | +inf.0 |
| Racket | 5710.411030625233 |
| Sagittarius | 5710.411030625233 |
| Scheme 9 | 5710.41103062521399 |
| STklos | +inf.0 |
| Tinyscheme | +inf.0 |
| Unsyntax | +inf.0 |
| Ypsilon | 5710.411030625233 |
| ABCL | error |
| CCL | 5710.411 |
| Clisp | 5710.411 |
| CMUCL | 5710.411 |
| ECL | 5710.411 |
| SBCL | 5710.411 |
| Emacs Lisp | 1.0e+INF |
x as the inexact infinity +inf.0.Another experiment:
(log 1/6319748715279270675921934218987893281199411530039296)Should return -119.27551918982401. (This was posted to the ECL mailing list on 2022-Jul-03 -- ECL does not compute the value, and complains about the user requesting log of zero).
-inf.0-inf.0-43.66827238All others return the correct result; Bigloo and Scheme9 need the rational to be described as division, not as rational type.