Re: [ANN] Lua 5.2.0 (rc7) now available
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- Subject: Re: [ANN] Lua 5.2.0 (rc7) now available
- From: KHMan <keinhong@...>
- Date: 2011年12月10日 04:37:14 +0800
On 12/10/2011 12:20 AM, Roberto Ierusalimschy wrote:
and the simple tests:
print(2^3 - 8)
-1.7763568394003e-015
print(3^4 - 81)
2.8421709430404e-014
=2^4-16
-1.7763568394003e-015
These all should be zero. It really seems that the 'pow' function
from the C library is broken.
The above results can be calculated as follows:
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
int main()
{
// from cygwin's newlib.c
// calculate x ** y as 2 ** (y log2(x))
double x, y, z;
x = 3; y = 4;
z = pow(2, y*log2(x));
printf("%g\n", z-81);
return 0;
}
This gives (MinGW gcc Win32):
$ gcc -o test test.c ; ./test
-2.84217e-014
Looking at newlib's math sources, more robust implementations of
pow() checks for integer exponents and handles that properly.
--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia