Second set of eyes - xmm calculations from IDA disassembly

[Tanaris4]

All-

I basically was wondering if someone else could take a look at this so I know I'm doing this properly, here is the pseudocode from IDA:

                    v4 = (__m128)*(_DWORD *)a2;
                    v4.m128_f32[0] = v4.m128_f32[0] - 17066.666;
                    v5 = (signed int)ffloor(COERCE_FLOAT(_mm_xor_ps(v4, (__m128)xmmword_8F6F60)) * 0.001875);
                    v6 = (__m128)*(_DWORD *)(a2 + 4);
                    v6.m128_f32[0] = v6.m128_f32[0] - 17066.666;

I believe (thanks for Apoc's help so far!) it may be as simple as: Math.Floor( (1/(val - 17066.666)) * 0.001875);

val basically just being a double of what is in location a2

Does this seem right? Am I completely off/incorrect?

Thanks in advance!
~ Tanaris

[Apoc]

Just pointing out that "xmmword_8F6F60" is -1 (128bit -1)

[Bananenbrot]

0.001875f == 3.0f/1600.0f == 1.0f/AdtWidth. And are you sure about having -1 rather than -0, which would be just the sign bit, at 0x8f6f60?
In either case your calculation is wrong. That snippet ought to calculate the adt tile coordinate from world coordinates. That is

const float AdtWidth = 1600.0f/3.0f;
const float MapOrigin = 32*AdtWidth; // == 17066.66666666f
var tileX = Math.Floor((MapOrigin - v.X) / AdtWidth);

The _mm_xor_ps does an xor on the result of (v.X - MapOrigin) with the sign bit, yielding the inverse, namely (MapOrigin - v.X). You get v by dereferencing a2.

[Tanaris4]

+rep ty bananenbrot!

Do you know where .029999999 comes from? A similar functino w/in the snippets I'm reversing basically has the exact same as the above, but changes .001875 to .029999

Snippet:

                v2 = (__m128)*(_DWORD *)(PositionPtr + 4);  // yPosition
                v2.m128_f32[0] = v2.m128_f32[0] - 17066.666;
                v3 = (signed int)ffloor(COERCE_FLOAT(_mm_xor_ps(v2, (__m128)xmmword_8F6F60)) * 0.029999999);
                v4 = (__m128)*(_DWORD *)PositionPtr;        // xPosition
                v4.m128_f32[0] = v4.m128_f32[0] - 17066.666;
                v5 = (signed int)ffloor(COERCE_FLOAT(_mm_xor_ps(v4, (__m128)xmmword_8F6F60)) * 0.029999999);

Edit: I'm basically trying to reverse CMap::QueryAreaIdTerrain and all it's sub functions

Edit 2: And based on what you just taught me, I believe the above in this post would translate to:

                const float AdtWidth = 1600.0f / 3.0f;
                const float MapOrigin = 32 * AdtWidth; // == 17066.66666666f

                float yPosition = Memory.ReadFloat((uint)PositionPtr + 4);  // yPosition
                v3 = (int)Math.Floor((MapOrigin - yPosition) * 0.029999999);
                //v3 = (signed int)ffloor(COERCE_FLOAT(_mm_xor_ps(v2, (__m128)xmmword_8F6F60)) * 0.029999999);

                float xPosition = Memory.ReadFloat((uint)PositionPtr);        // xPosition
                v5 = (int)Math.Floor((MapOrigin - xPosition) * 0.029999999);
                //v5 = (signed int)ffloor(COERCE_FLOAT(_mm_xor_ps(v4, (__m128)xmmword_8F6F60)) * 0.029999999);