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Date:	Thu, 07 Aug 2014 14:10:02 -0400
From:	Tim Prince <n8tm AT aol DOT com>
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Subject:	Re: suggestion about math.h
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On 8/7/2014 1:41 PM, Denis Excoffier wrote:
> Hello,
>
> Perhaps the values of some constants are not as accurate as they should be? See also M_LN2LO and M_LN2HI.
>
> diff -uNr cygwin-snapshot-20140807-1-original/newlib/libc/include/math.h cygwin-snapshot-20140807-1-patched/newlib/libc/include/math.h
> --- cygwin-snapshot-20140807-1-original/newlib/libc/include/math.h	2014-08-07 18:26:21.000000000 +0200
> +++ cygwin-snapshot-20140807-1-patched/newlib/libc/include/math.h	2014-08-07 19:31:51.000000000 +0200
> @@ -569,14 +569,14 @@
>   #ifndef __STRICT_ANSI__
>   
>   #define M_TWOPI         (M_PI * 2.0)
> -#define M_3PI_4		2.3561944901923448370E0
> -#define M_SQRTPI        1.77245385090551602792981
> +#define M_3PI_4		2.3561944901923449288E0
> +#define M_SQRTPI        1.77245385090551602729817
>   #define M_LN2LO         1.9082149292705877000E-10
>   #define M_LN2HI         6.9314718036912381649E-1
> -#define M_SQRT3	1.73205080756887719000
> +#define M_SQRT3	1.73205080756887729353
>   #define M_IVLN10        0.43429448190325182765 /* 1 / log(10) */
>   #define M_LOG2_E        _M_LN2
> -#define M_INVLN2        1.4426950408889633870E0  /* 1 / log(2) */
> +#define M_INVLN2        1.4426950408889634074E0  /* 1 / log(2) */
>   
>   /* Global control over fdlibm error handling.  */
>   
>
>
>
Without the L suffix, it doesn't look like it matters.
I just noticed this week the M_LN2LO and HI.  They should add up to a 
long double accurate constant.  I've been using a similar pair in 
implementation of exp() for 20 years.

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