Re: UBSAN error in lib/sh/random.c:79

[Steffen Nurpmeso]

Andreas Schwab wrote in
 <871qo6f90g.fsf@igel.home>:
 |On Jan 07 2023, Greg Wooledge wrote:
 |> The variable l is a modulus, so its largest possible value is 127772.
 |> If the code simply said "l = ret % 127773;" then it wouldn't even be
 |> an issue.  But the % was rewritten, presumably for efficiency.
 |
 |Presumably the assumption was that two divides are more costly than a
 |divide and a multiply (although nowadays, compilers will try to combine
 |the two divides if the target architecture has a divmod insn).

Seems to me that even twenty years ago gcc turned many divisions
into multiplications if it could.  (Which always stunned me as
a non-mathematician.)

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)