[Ohrrpgce] SVN: james/9631 The "experience to level" command now has a new optional hero slot argum

[Ralph Versteegen]

We have a bit of a problem: the xp formula produces different results in
gengcc=1 builds!

! TRACE: ASSERT FAILURE:
! TRACE: autotest.hss:1127: experience to level(2, bram slot) == 69 [actual
values were 70 == 69]

This would be because floating point calculations aren't totally
reproduceable between different CPU architectures, compilers, and build
options. The biggest problem is that the x87 FPU defaults to using 80 bit
registers, so it makes a difference whether a compiler puts an intermediate
result in a register or writes it out.
In this case, an intermediate result is 34.5, and it gets rounded
differently.

By coincidence, I read through the long discussion at
http://yosefk.com/blog/consistency-how-to-defeat-the-purpose-of-ieee-floating-point.html
about this just a week or two ago.

I've tried and confirmed that running the following linux-specific code to
use 64-bit instead of 80-bit x87 registers fixes the assert failure:
#include <fpu_control.h>
fpu_control_t cw;
_FPU_GETCW(cw);
cw = (cw & ~_FPU_EXTENDED) | _FPU_DOUBLE;
_FPU_SETCW(cw);

I read that this might have negative effects on the accuracy of math
functions like pow() implemented with library routines, but it'll be pretty
tiny.

I was planning on adding this anyway, to make scripts (once we add floating
point to HS) more portable between CPUs and builds.
But you're never going to avoid 100% of differences. For example the ARM
fpu in my phone gives larger errors on some math functions like exp, which
actually causes several tests in freebasic's test suite to fail.


On 1 November 2017 at 09:55, <subversion at hamsterrepublic.com> wrote:

> james
> 2017-10-31 13:55:49 -0700 (Tue, 31 Oct 2017)
> 208
> The "experience to level" command now has a new optional hero slot
> argument for checking the experience curve of a specific hero
> Also added a test-case to autotest.rpg verifying a customized experience
> curve
> ---
> U   wip/docs/plotdict.xml
> U   wip/docs/plotdictionary.html
> U   wip/plotscr.hsd
> U   wip/scriptcommands.bas
> U   wip/testgame/autotest.hss
> U   wip/testgame/autotest.rpg
> _______________________________________________
> Ohrrpgce mailing list
> ohrrpgce at lists.motherhamster.org
> http://lists.motherhamster.org/listinfo.cgi/ohrrpgce-motherhamster.org
>
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