Re issue #89: I'm confused. Isn't this true? Or is there something I'm not understanding about row vs. column major?
For example:

#include <stdio.h>
#include "HandmadeMath.h"

typedef hmm_mat4 mat4;
mat4 mat4Identity()
{
	return HMM_Mat4d(1.f);
}

void mat4Print(mat4 mat)
{
	int row = 0;
	while (row < 4)
	{
		printf("%d [%f %f %f %f]\n", row, mat[row][0], mat[row][1], mat[row][2], mat[row][3]);
		++row;
	}
}

int main()
{
	mat4 matA = mat4Identity();
	mat4Print(HMM_MultiplyMat4(matA, HMM_Translate({1.f, 2.f, 3.f})));
	mat4Print(HMM_Rotate(45.f, gUpAxis));
	return 0;
}

outputs:

0 [1.000000 0.000000 0.000000 0.000000]
1 [0.000000 1.000000 0.000000 0.000000]
2 [0.000000 0.000000 1.000000 0.000000]
3 [1.000000 2.000000 3.000000 1.000000]

0 [0.707107 0.000000 -0.707107 0.000000]
1 [0.000000 1.000000 0.000000 0.000000]
2 [0.707107 0.000000 0.707107 0.000000]
3 [0.000000 0.000000 0.000000 1.000000]

Which is what I expect: the translation (1.f, 2.f, 3.f) is properly stored in the 4th row of the matrix, where columns 1, 2, and 3 are contiguous in memory.

I did some more reading, and found this thorough discussion: Column Vectors vs. Row Vectors. I don't fully understand what they were getting at, but I think the terminology really should be clarified in Handmade Math.

Whether it's row-major or column-major depends on how you write it. My mat4Print prints it row-major, as if you were printing a pixel array (and not destroying your cache).

To clarify, the matrices are stored in row-major order, but you can choose to think of them in column-major order, right? I'm used to matrices being both stored and thought-of in row-major order, as if rendering the matrix out as a image stored from the top left corner, row by row.

However, it is row vector, which is what I expected, and what confused me when seeing "column-major". I think the terminology should be updated to say row-vector instead of column-major, because the latter is an ambiguous term.