SIMD instructions for floating point equality comparison (with NaN == NaN)

Question

Which instructions would be used for comparing two 128 bit vectors consisting of 4 * 32-bit floating point values?

Is there an instruction that considers a NaN value

Answer 1

Here is one possible solution - it's not very efficient however, requiring 6 instructions:

__m128 v0, v1; // float vectors

__m128 v0nan = _mm_cmpeq_ps(v0, v0);                   // test v0 for NaNs
__m128 v1nan = _mm_cmpeq_ps(v1, v1);                   // test v1 for NaNs
__m128 vnan = _mm_or_si128(v0nan, v1nan);              // combine
__m128 vcmp = _mm_cmpneq_ps(v0, v1);                   // compare floats
vcmp = _mm_and_si128(vcmp, vnan);                      // combine NaN test
bool cmp = _mm_testz_si128(vcmp, vcmp);                // return true if all equal

Note that all the logic above is inverted, which may make the code a little hard to follow (ORs are effectively ANDs, and vice versa).