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Define built-in constants and add two circle constants #4473

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Start built-in constants section
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Start built-in constants section
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mehmetoguzderin committed Jan 31, 2024
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32 changes: 32 additions & 0 deletions wgsl/index.bs
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Expand Up @@ -17492,6 +17492,38 @@ All synchronization functions [=shader-creation error|must=] only be invoked in
space.
</table>

# Built-in Constants # {#builtin-constants}

<dfn noexport>Built-in constants</dfn> are [=predeclared=] values provided by
the implementation and, therefore, always available for use in a WGSL module.
All built-in constants are [=const-declarations=], and all their names are
valid [=identifiers=].

Note: The built-in constants with
[[#abstract-types|abstract numeric types]] that represent symbolic
values are subject to the same rules, including
[[#abstract-float-accuracy|abstract float accuracy]]. As such, where
applicable, expressions involving them might be evaluated at
[=shader module creation|shader-creation time=] and
and result in better approximations than operating on target types, reducing
the need for specializations such as `PI_2` for scales and offsets.

<table class='data builtin constants'>
<caption>
<dfn noexport>Built-in mathematical constants</dfn>
</caption>
<thead>
<tr><th>Names<th>Type<th>Description
</thead>
<tr><td>`PI`, `π`<td>[=abstractfloat|AbstractFloat=]<td>Approximates the ratio of the
circumference of a circle to its diameter, known as π, pi, or Archimedes'
constant.
<tr><td>`TAU`, `τ`<td>[=abstractfloat|AbstractFloat=]<td>Approximates the perimeter of a
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@Kangz Kangz Jan 31, 2024

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Any other constants we need? e or phi for example?

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@mehmetoguzderin mehmetoguzderin Jan 31, 2024

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@Kangz I think that e is certainly a good addition in terms of practicality, though group decided to start with pi and tau initially. If there's consensus, I can certainly add to PR

unit circle, known as τ, tau, 2π, or a turn.
</thead>
</table>
</div>

# Grammar for Recursive Descent Parsing # {#grammar-recursive-descent}

This section is non-normative.
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