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fix(matrix4): Prevent undefined behavior when comparing Matrix4x4 bits #3651

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fix(matrix4): Prevent undefined behavior when comparing Matrix4x4 bits #3651

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refactor(wwmath): Compare Matrix4x4 element bits with std::bit_cast
CryoTheRenegade Oct 23, 2026
006c62b
refactor(wwmath): Compare Matrix4x4 bits with memcmp
CryoTheRenegade Nov 3, 2026
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13 changes: 3 additions & 10 deletions Core/Libraries/Source/WWVegas/WWMath/matrix4.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@
#include "WWLib/win.h"
#include <d3d8types.h>
#include <d3dx8math.h>
#include <string.h>

/***********************************************************************************************
* Matrix4x4::Multiply -- Multiply two Matrix4x4's together *
Expand Down Expand Up @@ -180,18 +181,10 @@ void Matrix4x4::Multiply(const Matrix4x4 & a,const Matrix3D & b,Matrix4x4 * res)
#undef ROWCOL4
}

// Compares the bits of the elements, so 0.0f and -0.0f differ and identical NaNs are equal.
int operator == (const Matrix4x4 & a, const Matrix4x4 & b)
{
unsigned* m1=(unsigned*)&a;
unsigned* m2=(unsigned*)&b;
unsigned res=0;
for (int i=0;i<4;++i) {
res|=*m1++^*m2++;
res|=*m1++^*m2++;
res|=*m1++^*m2++;
res|=*m1++^*m2++;
}
return !res;
return memcmp(&a, &b, sizeof(Matrix4x4)) == 0;

@xezon xezon Nov 7, 2026

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Why do other math 3d types do not compare like this?

For example Matrix3D:

WWINLINE bool operator == (const Matrix3D &A, const Matrix3D &B)
{
   for (int i = 0; i < 3; i++) {
      for (int j = 0; j < 4; j++) {
         if (A[i][j] != B[i][j]) return false;
      }
   }
   return true;
}

Would that act different when using memcmp?

@CryoTheRenegade CryoTheRenegade Nov 8, 2026

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Yes, it differs in two cases:

  • 0.0f vs -0.0f: float != says equal, memcmp says different.
  • NaN: float != says a NaN never equals anything, even itself. memcmp says two NaNs with the same bits are equal.

For all other values they agree.

The original Matrix4x4 code already compared bits (it read the floats as unsigned), so this PR keeps that behavior and only removes the pointer casts. Matrix3D and Matrix3x3 have always compared float values. My guess is the bit compare was there to keep float compares out of the D3D transform cache in DX8Wrapper::_Set_DX8_Transform. That is the only use I found, and it is disabled with #if 0.

}

int operator != (const Matrix4x4 & a, const Matrix4x4 & b)
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