Re: [Maxima-discuss] scale-float with sbcl & ccl

[Raymond T. <toy...@gm...>]

On 12/5/25 10:21 AM, Barton Willis via Maxima-discuss wrote:
>
> For subnormal floats,  the SBCL CL function scale-float is possibly buggy:
>
> SBCL 2.4.7:
>
> Define Maxima function that calls the CL function scale-float
>
> (%i1) :lisp(defun $scale_float (x m) (scale-float x m))
>
> (%i1) x : 2.0^(-1024);
> (%o1)                       5.562684646268004e-309
>
> This is a SBCL bug, I think:  surely scaling by zero should be an 
> identity?
>
> (%i2) scale_float(x,0);
> (%o2)                       2.7813423231340017e-308
>
> (%i3) x : 2.0^(-1023);
> (%o3)                       1.1125369292536007e-308
This is kinda surprising.  Cmucl gets this right.  So does ecl. Kinda 
funny too; it's not obvious what's happening here. 
`integer-decode-float` for the scaled result is `#x14000000000000` and 
an exponent of -1074, instead of the expected `#x10000000000000` with 
exponent -1076.