PRVM: Return NaN/inf values for divisions by zero.

[divVerent]

Also improve accuracy of DIV_VF a bit.

This matches FTEQW.

[hemebond]

Compiles fine, and no crashes, but I don't see the new cvar, and doing float foobar = 1 / 0; does nothing; no crash or error or warning. Not sure how to test this.

[divVerent]

Thanks; as for testing, you can't just write float foobar = 1 / 0, as this will be evaluated by the compiler.

To have a good chance of testing this, add to your game:

float autocvar_div0_a;
float autocvar_div0_b;
// In worldspawn:
void() worldspawn = {
  cvar_set("div0_a", "1");
  cvar_set("div0_b", "1");
  // The other stuff from before.
};
// Then in the StartFrame function:
void() StartFrame = {
  dprint("div0_a / div0_b = ", ftos(autocvar_div0_a / autocvar_div0_b), "\n");
  // The other stuff from before.
};

Then launch a game and perform on the console:

] developer 1
div0_a / div0_b = 1.000000
div0_a / div0_b = 1.000000
div0_a / div0_b = 1.000000
div0_a / div0_b = 1.000000
] set div0_b 0
WARNING: Attempted division ...
div0_a / div0_b = inf
WARNING: Attempted division ...
div0_a / div0_b = inf
WARNING: Attempted division ...
div0_a / div0_b = inf
] prvm_gameplayfix_div0is0 1
WARNING: Attempted division ...
div0_a / div0_b = 0.000000
WARNING: Attempted division ...
div0_a / div0_b = 0.000000
WARNING: Attempted division ...
div0_a / div0_b = 0.000000

I have not tested it yet, but this is the expected outcome.

[divVerent]

Testing it myself now, now that I've written that code anyway. When using a more modern compiler, one can skip the cvar_set calls and just use:

var float autocvar_div0_a = 1;
var float autocvar_div0_b = 1;
void() StartFrame = {
  dprint("div0_a / div0_b = ", ftos(autocvar_div0_a / autocvar_div0_b), "\n");
  // The other stuff from before.
};

[divVerent]

Yes, just confirmed it myself.

As a minor difference from expectations, DP prints -nan for the NaN result. I do not know why, but it does not really matter and is also pre-existing in ftos.

[divVerent]

To be clear, the expectations are:

positive / 0 = inf
0 / 0 = nan or -nan
-0 / 0 = nan or -nan
negative / 0 = -inf
positive / -0 = -inf
0 / -0 = nan or -nan
-0 / -0 = nan or -nan
negative / -0 = inf

Generating a working -0 is left as an exercise to the reader.

[hemebond]

Tested and working as documented in the PR comments.