Intel Intrinsics — AVX & AVX2 Learning Notes
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Fundamentals of AVX Programming#
Data Types#
Data Type Description
__m128
128-bit vector containing 4 float
s
__m128d
128-bit vector containing 2 double
s
__m128i
128-bit vector containing integers
__m256
256-bit vector containing 8 float
s
__m256d
256-bit vector containing 4 double
s
__m256i
256-bit vector containing integers
- Each type starts with two underscores, an
m
, and the width of the vector in bits.- If a vector type ends in
d
, it containsdouble
s, and if it doesn’t have a suffix, it containsfloat
s.- An integer vector type can contain any type of integer, from
char
s toshort
s tounsigned long long
s. That is, an_m256i
may contain 32char
s, 16short
s, 8int
s, or 4long
s. These integers can be signed or unsigned.
Function Naming Conventions#
_mm<bit_width>_<name>_<data_type>
<bit_width>
identifies the size of the vector returned by the function. For 128-bit vectors, this is empty. For 256-bit vectors, this is set to256
.<name>
describes the operation performed by the intrinsic<data_type>
identifies the data type of the function’s primary arguments
ps
- vectors containfloat
s (ps
stands for packed single-precision)pd
- vectors containdouble
s (pd
stands for packed double-precision)epi8/epi16/epi32/epi64
- vectors contain 8-bit/16-bit/32-bit/64-bit signed integersepu8/epu16/epu32/epu64
- vectors contain 8-bit/16-bit/32-bit/64-bit unsigned integerssi128
/si256
- unspecified 128-bit vector or 256-bit vectorm128/m128i/m128d/m256/m256i/m256d
- identifies input vector types when they’re different than the type of the returned vector
A data type represents memory and a function represents a multimedia operation, so the AVX data types start with two underscores with an
m
, AVX functions start with an underscore with twom
s .
Initialization Intrinsics#
Initialization with Scalar Values#
Function Description
_mm256_setzero_ps/pd
Returns a floating-point vector filled with zeros
_mm256_setzero_si256
Returns an integer vector whose bytes are set to zero
_mm256_set1_ps/pd
Fill a vector with a floating-point value
_mm256_set1_epi8/epi16/epi32/epi64x
Fill a vector with an integer
_mm256_set_ps/pd
Initialize a vector with eight floats (ps)or four doubles (pd)
_mm256_set_epi8/epi16/epi32/epi64x
Initialize a vector with integers
_mm256_set_m128/m128d/m128i
Initialize a 256-bit vector with two 128-bit vectors
_mm256_setr_ps/pd
Initialize a vector with eight floats (ps) or four doubles (pd) in reverse order
_mm256_setr_epi8/epi16/epi32/epi64x
Initialize a vector with integers in reverse order
Loading Data from Memory#
Data Type Description
_mm256_load_ps/pd
Loads a floating-point vector from an aligned memory address
_mm256_load_si256
Loads an integer vector from an aligned memory address
_mm256_loadu_ps/pd
Loads a floating-point vector from an unaligned memory address
_mm256_loadu_si256
Loads an integer vector from an unalignedmemory address
_mm_maskload_ps/pd
_mm256_maskload_ps/pd
Load portions of a 128-bit/256-bitfloating-point vector according to a mask
(2)_mm_maskload_epi32/64
(2)_mm256_maskload_epi32/64
Load portions of a 128-bit/256-bitinteger vector according to a mask
The last two functions are preceded with
(2)
because they’re provided by AVX2, not AVX.
Each
_mm256_load_*
intrinsic accepts a memory address that must be aligned on a 32-byte boundary.
Arithmetic Intrinsics#
Addition and Subtraction#
Data Type Description
_mm256_add_ps/pd
Add two floating-point vectors
_mm256_sub_ps/pd
Subtract two floating-point vectors
(2)_mm256_add_epi8/16/32/64
Add two integer vectors
(2)_mm236_sub_epi8/16/32/64
Subtract two integer vectors
(2)_mm256_adds_epi8/16
(2)_mm256_adds_epu8/16
Add two integer vectors with saturation
(2)_mm256_subs_epi8/16
(2)_mm256_subs_epu8/16
Subtract two integer vectors with saturation
_mm256_hadd_ps/pd
Add two floating-point vectors horizontally
_mm256_hsub_ps/pd
Subtract two floating-point vectors horizontally
(2)_mm256_hadd_epi16/32
Add two integer vectors horizontally
(2)_mm256_hsub_epi16/32
Subtract two integer vectors horizontally
(2)_mm256_hadds_epi16
Add two vectors containing shorts horizontally with saturation
(2)_mm256_hsubs_epi16
Subtract two vectors containing shorts horizontally with saturation
_mm256_addsub_ps/pd
Add and subtract two floating-point vectors
Functions that take saturation into account clamp the result to the minimum/maximum value that can be stored. Functions without saturation ignore the memory issue when saturation occurs.
This may seem strange to add and subtract elements horizontally, but these operations are helpful when multiplying complex numbers.
_mm256_addsub_ps/pd
, alternately subtracts and adds elements of two floating-point vectors. That is, even elements are subtracted and odd elements are added .
Multiplication and Division#
Data Type Description
_mm256_mul_ps/pd
Multiply two floating-point vectors
(2)_mm256_mul_epi32
(2)_mm256_mul_epu32
Multiply the lowest four elements of vectors containing 32-bit integers
(2)_mm256_mullo_epi16/32
Multiply integers and store low halves
(2)_mm256_mulhi_epi16
(2)_mm256_mulhi_epu16
Multiply integers and store high halves
(2)_mm256_mulhrs_epi16
Multiply 16-bit elements to form 32-bit elements
_mm256_div_ps/pd
Divide two floating-point vectors
This image is WRONG !!!
Please read the reference from this manual.
Only the four low elements of the
_mm256_mul_epi32
and_mm256_mul_epu32
intrinsics are multiplied together, and the result is a vector containing four long integers.
They multiply every element of both vectors store only the low half of each product
Fused Multiply and Add (FMA)#
Data Type Description
(2)_mm_fmadd_ps/pd/
(2)_mm256_fmadd_ps/pd
Multiply two vectors and add the product to a third (res = a * b + c)
(2)_mm_fmsub_ps/pd/
(2)_mm256_fmsub_ps/pd
Multiply two vectors and subtract a vector from the product (res = a * b - c)
(2)_mm_fmadd_ss/sd
Multiply and add the lowest element in the vectors (res[0] = a[0] * b[0] + c[0])
(2)_mm_fmsub_ss/sd
Multiply and subtract the lowest element in the vectors (res[0] = a[0] * b[0] - c[0])
(2)_mm_fnmadd_ps/pd
(2)_mm256_fnmadd_ps/pd
Multiply two vectors and add the negated product to a third (res = -(a * b) + c)
(2)_mm_fnmsub_ps/pd/
(2)_mm256_fnmsub_ps/pd
Multiply two vectors and add the negated product to a third (res = -(a * b) - c)
(2)_mm_fnmadd_ss/sd
Multiply the two lowest elements and add the negated product to the lowest element of the third vector (res[0] = -(a[0] * b[0]) + c[0])
(2)_mm_fnmsub_ss/sd
Multiply the lowest elements and subtract the lowest element of the third vector from the negated product (res[0] = -(a[0] * b[0]) - c[0])
(2)_mm_fmaddsub_ps/pd/
(2)_mm256_fmaddsub_ps/pd
Multiply two vectors and alternately add and subtract from the product (res = a * b +/- c) (Odd add, even sub)
(2)_mm_fmsubadd_ps/pd/
(2)_mmf256_fmsubadd_ps/pd
Multiply two vectors and alternately subtract and add from the product (res = a * b -/+ c) (Odd sub, even add)
Permuting and Shuffling#
Permuting#
Data Type Description
_mm_permute_ps/pd
_mm256_permute_ps/pd
Select elements from the input vector based on an 8-bit control value
(2)_mm256_permute4x64_pd/
(2)_mm256_permute4x64_epi64
Select 64-bit elements from the input vector based on an 8-bit control value
_mm256_permute2f128_ps/pd
Select 128-bit chunks from two input vectors based on an 8-bit control value
_mm256_permute2f128_si256
Select 128-bit chunks from two input vectors based on an 8-bit control value
_mm_permutevar_ps/pd
_mm256_permutevar_ps/pd
Select elements from the input vector based on bits in an integer vector
(2)_mm256_permutevar8x32_ps
(2)_mm256_permutevar8x32_epi32
Select 32-bit elements (float
s and int
s) using indices in an integer vector
Shuffling#
Data Type Description
_mm256_shuffle_ps/pd
Select floating-point elements according to an 8-bit value
_mm256_shuffle_epi8/
_mm256_shuffle_epi32
Select integer elements according to an8-bit value
(2)_mm256_shufflelo_epi16/
(2)_mm256_shufflehi_epi16
Select 128-bit chunks from two input vectors based on an 8-bit control value
For
_mm256_shuffle_pd
, only the high four bits of the control value are used. If the input vectors containint
s orfloat
s, all the control bits are used. For_mm256_shuffle_ps
, the first two pairs of bits select elements from the first vector and the second two pairs of bits select elements from the second vector.
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