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c++sseintrinsicsavx

AVX: "to 1 if not zero"

How can I turn the values of array of float32 numbers to 1 if they are not zero, using AVX?

For example: -0.2134f, -1.23f, -0.0f, 12.0f ...

becomes 1.0f, 1.0f, 0.0f, 1.0f ...

I assume, we should combine _mm256_or_ps with some other instruction, but how?

Solution

  • The first idea I would come up with is comparing the values to 0 and then ANDing that with a register full of 1s:

    y = _mm256_and_ps(_mm256_cmp_ps(_mm256_setzero_ps(), x, _CMP_NEQ_OQ), _mm256_set1_ps(1.f));

    This will AND all the 1s in the places where x is 0 with a bunch of 0s and fortunately an IEEE 754 zero is also an integer zero. The other values will get a floating point 1 ANDed with a bunch of 1s and thus an identity operation.