Re: [PATCH] fix llrint and lrint for 52 <= exponent <= 62

[Corinna Vinschen <vinschen at redhat dot com>]

Hi Matthias,

On May 14 14:38, Matthias J. Kannwischer wrote:
> lrint and llrint produce wrong results if the exponent is between 52 and 62. 
> e.g. llrint(2.308393893084546048E18) returns 146666059061806080 instead of 2308393893084546048. 
> Can you confirm this?
> I've tracked this down to two mistakes in s_llrint.c/s_lrint.c (one missing 0 and one uint32 overflow), see patch below. 
> 
> Cheers, 
> Matthias
> 
> ---
>  newlib/libm/common/s_llrint.c | 4 ++--
>  newlib/libm/common/s_lrint.c  | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/newlib/libm/common/s_llrint.c b/newlib/libm/common/s_llrint.c
> index 8b8a846ae..72452dbe9 100644
> --- a/newlib/libm/common/s_llrint.c
> +++ b/newlib/libm/common/s_llrint.c
> @@ -93,9 +93,9 @@ long long int
>        if (j0 >= 52)
>         /* 64bit return: j0 in [52,62] */
>         /* 64bit return: left shift amt in [32,42] */
> -        result = ((long long int) ((i0 & 0x000fffff) | 0x0010000) << (j0 - 20)) | 
> +        result = ((long long int) ((i0 & 0x000fffff) | 0x00100000) << (j0 - 20)) |
>                 /* 64bit return: right shift amt in [0,10] */
> -                   (i1 << (j0 - 52));
> +                   ((long long int) i1 << (j0 - 52));
>        else
>          {
>           /* 64bit return: j0 in [20,51] */
> diff --git a/newlib/libm/common/s_lrint.c b/newlib/libm/common/s_lrint.c
> index 9d2cb7306..b37f50fd4 100644
> --- a/newlib/libm/common/s_lrint.c
> +++ b/newlib/libm/common/s_lrint.c
> @@ -131,9 +131,9 @@ TWO52[2]={
>        if (j0 >= 52)
>         /* 64bit return: j0 in [52,62] */
>         /* 64bit return: left shift amt in [32,42] */
> -        result = ((long int) ((i0 & 0x000fffff) | 0x0010000) << (j0 - 20)) | 
> +        result = ((long int) ((i0 & 0x000fffff) | 0x00100000) << (j0 - 20)) |
>                 /* 64bit return: right shift amt in [0,10] */
> -                   (i1 << (j0 - 52));
> +                   ((long int) i1 << (j0 - 52));
>        else
>          {
>           /* 32bit return: j0 in [20,30] */
> -- 
> 2.14.3
> 

Looks right to me, but can you resend the patch as attachment, please?
Your MUA apparently replaced tabs with spaces.


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

Attachment: signature.asc
Description: PGP signature