[simd.ctor]

# 29 Numerics library [[numerics]](./#numerics)

## 29.10 Data-parallel types [[simd]](simd#ctor)

### 29.10.7 Class template basic_vec [[simd.class]](simd.class#simd.ctor)

#### 29.10.7.2 basic_vec constructors [simd.ctor]

[ð](#lib:basic_vec,constructor)

`template<class U> constexpr explicit(see below) basic_vec(U&& value) noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17699)

Let From denote the type remove_cvref_t<U>[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17702)

*Constraints*: value_type satisfies [constructible_from](concept.constructible#concept:constructible_from "18.4.11 Concept constructible_­from [concept.constructible]")<U>[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17706)

*Effects*: Initializes each element to the value of the argument after conversion tovalue_type[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17711)

*Remarks*: The expression inside explicit evaluates to false if and only ifU satisfies [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<value_type>, and either

- [(4.1)](#4.1)

From is not an arithmetic type and does not satisfy [*constexpr-wrapper-like*](simd.expos#concept:constexpr-wrapper-like "29.10.2 Exposition-only types, variables, and concepts [simd.expos]"),

- [(4.2)](#4.2)

From is an arithmetic type and the conversion from From to value_type is value-preserving ([[simd.general]](simd.general "29.10.1 General")), or

- [(4.3)](#4.3)

From satisfies [*constexpr-wrapper-like*](simd.expos#concept:constexpr-wrapper-like "29.10.2 Exposition-only types, variables, and concepts [simd.expos]"), remove_const_t<decltype(From​::​value)> is an arithmetic type, and From​::​value is representable by value_type[.](#4.sentence-1)

[ð](#lib:basic_vec,constructor_)

`template<class U, class UAbi>
  constexpr explicit(see below) basic_vec(const basic_vec<U, UAbi>& x) noexcept;
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17736)

*Constraints*: *simd-size-v*<U, UAbi> == size() is true[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17740)

*Effects*: Initializes the ith element with static_cast<T>(x[i]) for
all i in the range of [0, size())[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17745)

*Remarks*: The expression inside explicit evaluates to true if either

- [(7.1)](#7.1)

the conversion from U to value_type is not value-preserving,
 or

- [(7.2)](#7.2)

both U and value_type are integral types and the integer
 conversion rank ([[conv.rank]](conv.rank "6.9.6 Conversion ranks")) of U is greater than the integer
 conversion rank of value_type, or

- [(7.3)](#7.3)

both U and value_type are floating-point types and the
 floating-point conversion rank ([[conv.rank]](conv.rank "6.9.6 Conversion ranks")) of U is greater than
 the floating-point conversion rank of value_type[.](#7.sentence-1)

[ð](#lib:basic_vec,constructor__)

`template<class G> constexpr explicit basic_vec(G&& gen);
`

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17769)

Let Fromi denote the typedecltype(gen(integral_constant<*simd-size-type*, i>()))[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17773)

*Constraints*: Fromi satisfies [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<value_type> for all i in
the range of [0, size())[.](#9.sentence-1)

In addition, for all i in the range of [0, size()), if Fromi is an arithmetic type, conversion from Fromi to value_type is value-preserving[.](#9.sentence-2)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17781)

*Effects*: Initializes the ith element withstatic_cast<value_type>(gen(integral_constant<*simd-​size-​type*,
i>())) for all i in the range of [0, size())[.](#10.sentence-1)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17787)

*Remarks*: gen is invoked exactly once for each i, in increasing order of i[.](#11.sentence-1)

[ð](#lib:basic_vec,constructor___)

`template<class R, class... Flags>
  constexpr basic_vec(R&& r, flags<Flags...> = {});
template<class R, class... Flags>
  constexpr basic_vec(R&& r, const mask_type& mask, flags<Flags...> = {});
`

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17801)

Let mask be mask_type(true) for the overload with nomask parameter[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17805)

*Constraints*: 

- [(13.1)](#13.1)

R models ranges​::​[contiguous_range](range.refinements#concept:contiguous_range "25.4.6 Other range refinements [range.refinements]") and ranges​::​[sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]"),

- [(13.2)](#13.2)

ranges​::​size(r) is a constant expression, and

- [(13.3)](#13.3)

ranges​::​size(r) is equal to size()[.](#13.sentence-1)

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17814)

*Mandates*: 

- [(14.1)](#14.1)

ranges​::​range_value_t<R> is a vectorizable type, and

- [(14.2)](#14.2)

if the template parameter pack Flags does not contain *convert-flag*, then the conversion from ranges​::​range_value_t<R> to value_type is value-preserving[.](#14.sentence-1)

[15](#15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17825)

*Preconditions*: 

- [(15.1)](#15.1)

  If the template parameter pack Flags contains *aligned-flag*, ranges​::​data(r) points to
 storage aligned by alignment_v<basic_vec,
 ranges​::​range_value_t<R>>[.](#15.1.sentence-1)

- [(15.2)](#15.2)

  If the template parameter pack Flags contains *overaligned-flag*<N>, ranges​::​data(r) points to
 storage aligned by N[.](#15.2.sentence-1)

[16](#16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17839)

*Effects*: Initializes the ith element with mask[i] ?static_cast<T>(​ranges​::​​data(r)[i]) : T() for all i in the
range of [0, size())[.](#16.sentence-1)

[ð](#itemdecl:5)

`template<class R, class... Ts>
  basic_vec(R&& r, Ts...) -> see below;
`

[17](#17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17852)

*Constraints*: 

- [(17.1)](#17.1)

R models ranges​::​[contiguous_range](range.refinements#concept:contiguous_range "25.4.6 Other range refinements [range.refinements]") and ranges​::​[sized_range](range.sized#concept:sized_range "25.4.4 Sized ranges [range.sized]"), and

- [(17.2)](#17.2)

ranges​::​size(r) is a constant expression[.](#17.sentence-1)

[18](#18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17860)

*Remarks*: The deduced type is equivalent to vec<ranges​::​range_value_t<R>,
ranges​::​size(r)>[.](#18.sentence-1)

[ð](#lib:basic_vec,constructor____)

`template<[simd-floating-point](simd.expos#concept:simd-floating-point "29.10.2 Exposition-only types, variables, and concepts [simd.expos]") V>
  constexpr explicit(see below)
    basic_vec(const V& reals, const V& imags = {}) noexcept;
`

[19](#19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17874)

*Constraints*: 

- [(19.1)](#19.1)

[*simd-complex*](simd.expos#concept:simd-complex "29.10.2 Exposition-only types, variables, and concepts [simd.expos]")<basic_vec> is modeled, and

- [(19.2)](#19.2)

V​::​size() == size() is true[.](#19.sentence-1)

[20](#20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17883)

*Effects*: Initializes the ith element with value_type(reals[i],
imags[i]) for all i in the range [0, size())[.](#20.sentence-1)

[21](#21)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L17888)

*Remarks*: The expression inside explicit evaluates to false if and only
if the floating-point conversion rank of T​::​value_type is greater than
or equal to the floating-point conversion rank of V​::​value_type[.](#21.sentence-1)
