On Tue, Dec 3, 2024 at 8:24 AM 蒋力夫 Lifu JIANG <lifuji...@hkust-gz.edu.cn> wrote:
>
> In the following two files:
> gcc/libquadmath/math/expq.c
> glibc/blob/master/sysdeps/ieee754/ldbl-128/e_expl.c
It looks like a bug to me. I suggest filing one on the glibc side.
Uses:
/* Calculate t/32768. */
t = x + THREEp96;
t -= THREEp96;
and iff
/* Calculate t/256. */
t = x + THREEp103;
t -= THREEp103;
is correct then indeed it's supposed to be THREEp96 and not THREEp94.
> --------------------------------------------------------------------
> static const __float128 C[] = {
> /* Smallest integer x for which e^x overflows. */
> #define himark C[0]
> 11356.523406294143949491931077970765Q,
>
> /* Largest integer x for which e^x underflows. */
> #define lomark C[1]
> -11433.4627433362978788372438434526231Q,
>
> /* 3x2^96 */
> #define THREEp96 C[2]
> 237684487542793012780631851008.0Q,
>
> /* 3x2^103 */
> #define THREEp103 C[3]
> 30423614405477505635920876929024.0Q,
>
> /* 3x2^111 */
> #define THREEp111 C[4]
> 7788445287802241442795744493830144.0Q,
> --------------------------------------------------------------------
>
> Why is 3x2^96 defined as 59421121885698253195157962752 instead of
> 237684487542793012780631851008?
> 3x2^94=59421121885698253195157962752,
> 3x2^96=237684487542793012780631851008,
> 3x2^103=30423614405477505635920876929024,
> 3x2^111=7788445287802241442795744493830144.
>
