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Hi all,
As you might know, AVX does not provide instructions for integer types, which are planned to arrive with AVX2. I have a code written using AVX instructions, which basically use _mm256_*_pd() variants of instructions that operate on double-precision floating-point values (the instructions I use are min, max, shuffle, blend, load, loadu, etc.). However my data is actually integers, which I load by casting integer pointers to double pointers, i.e. __m256d reg = _mm256_loadu_pd((double*)intPtr) etc. Functionality wise the code seems to do what I expect, i.e. sorts the data. However, as I haven't tested with all sorts of different data, I'm concerned whether the output will always be correct. What corner cases should I be concerned with? Would the comparisons will always be correct or will there be some integer values where the AVX floating point comparison would not work?
Thanks for comments and suggestions
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Once again, this is not possible to create a NaN value in a double precision variable from a 64-bit integer variable by doing a simple cast.Of course. The original question however involved casting pointers, not data values: _mm256_loadu_pd((double*)intPtr).
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If a value in the second operand is an SNaN, that SNaN is forwarded unchanged to the destination (that is, a QNaN version of the SNaN is not returned). If only one value is a NaN (SNaN or QNaN) for this instruction, the second operand (source operand), either a NaN or a valid floating-point value, is written to the result.In your case, one of the elements of the 2nd operand is a NaN, so that NaN is forwarded to the destination operand. As to your second point: depending on your floating-point environment, subnormals (exponent == 0, significand != 0; i.e., non-zero integers with "small" absolute value) might cause exceptions to be raised. I don't know what would happen if you have "flush-to-zero" enabled and you compare two vectors of small, non-zero integers. I'm sure the behavior is defined; I just don't know what it is.
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