Aussie AI
AVX Operations
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Book Excerpt from "Generative AI in C++"
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by David Spuler, Ph.D.
AVX Operations
The main SIMD instructions are called “vertical” instructions, by convention. They take one vector and a second vector (e.g. both are 128-bit), apply an operation element-wise in parallel, and put the result into a third register. In other words, they return the result of a “pair-wise” or “element-wise” operation on two vectors into a third vector.
For example, vertical addition requires two input vectors and will output a third vector with the sums.
AVX-512 SIMD addition will add two 512-bit registers full of float values
on a paired element basis (i.e. adds 16 pairs of 32-bit float values), yielding a third 512-bit vector with the result (16 float values).
Binary operations. The full list of binary AVX operations is very long. Supported AVX operations include:
- Multiplication
- Addition
- Subtraction
- Division
- Maximum
- Minimum
- Fused Multiply-Add (FMA)
- Bitwise operations
- ...and many more
Unary operations. AVX unary intrinsics apply a particular function to all elements of an AVX register in parallel, and return the resulting register. Supported AVX unary operations include:
- Clear to zero
- Set to a constant
- Casts
- Conversions
- Popcount (POPCNT)
- Leading-zero count (LZCNT)
Mathematical Functions. Simple float-to-float mathematical functions are effectively a type of unary operator. AVX supports a variety of functions with vector hardware instructions, such as:
- Absolute value:
abs - Error function:
erf - Reciprocal
- Rounding, ceiling, floor
- Roots:
sqrt(square root), cube root - Inverted roots (e.g.
invsqrt) - Exponential:
exp,exp10 - Logarithm:
log,log10 - Trigonometric functions
- Hyperbolic functions
- Statistics (e.g. Cumulative Distribution Function)
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