mirabilos added the comment:
mirabilos dixit:
>mirabilos added the comment:
>Yes, that’s precisely what’s not working on the most widespread
>emulator, at the very least. (I have working code for that, in
>three(!) variants, but it just ignores those requests to change
>precision.)
Here’s the Python testcase made into a standalone test:
-----BEGIN cutting here may damage your screen surface-----
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#ifndef __MirBSD__
#include <fpu_control.h>
#endif
void runtests(void);
void
runtests(void)
{
volatile double x, y, z;
/* 1./(1-2**-53) -> 1+2**-52 (correct), 1.0 (double rounding) */
x = 0.99999999999999989; /* 1-2**-53 */
y = 1./x;
printf("test#1 %s: %.17E\n", (y == 1.) ? "fail" : "good", y);
/* 1e16+2.99999 -> 1e16+2. (correct), 1e16+4. (double rounding) */
x = 1e16;
y = 2.99999;
z = x + y;
printf("test#2 %s: %.17E\n", z == 1e16+4. ? "fail" : "good", z);
}
int
main(void) {
#ifdef _FPU_SETCW
fpu_control_t cwold, cwnew, cwgot;
#endif
runtests();
#if (defined(__i386__) || defined(__m68k__)) && defined(_FPU_SETCW)
_FPU_GETCW(cwold);
#ifdef __i386__
cwnew = 0x127f;
#else
cwnew = _FPU_RC_NEAREST | _FPU_DOUBLE;
#endif
_FPU_SETCW(cwnew);
_FPU_GETCW(cwgot);
printf("changing FPU control word from %08X to %08X => %08X\n",
cwold, cwnew, cwgot);
runtests();
#endif
return (0);
}
-----END cutting here may damage your screen surface-----
Here’s the result of running it on the latest ARAnyM, which
did get MPFR-based FPU emulation bugfixes, but apparently
still ignores any FPUCW changes (or, at least the ones relating
to precision):
root@ara3:~ # ./a.out
test#1 fail: 1.00000000000000000E+00
test#2 fail: 1.00000000000000040E+16
changing FPU control word from 00000000 to 00000080 => 00000080
test#1 fail: 1.00000000000000000E+00
test#2 fail: 1.00000000000000040E+16
bye,
//mirabilos
--
"Using Lynx is like wearing a really good pair of shades: cuts out
the glare and harmful UV (ultra-vanity), and you feel so-o-o COOL."
-- Henry Nelson, March 1999
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue18062>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
