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encode discriminants as LE uints
https://github.com/WebAssembly/component-model/pull/336/files/88e6d8fd597a1e2cac4d30a43a4bb053692a84e7#diff-59f6b20b0bd073593bb31d6338e2186f876564ffe0bb67b8740b37dabf8e5636 Signed-off-by: Roman Volosatovs <[email protected]>
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‎design/mvp/Binary.md‎

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Original file line numberDiff line numberDiff line change
@@ -358,40 +358,46 @@ Notes:
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(See [Value Definitions](Explainer.md#value-definitions) in the explainer.)
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```ebnf
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value ::= t:<valtype> len:<uN> v:<val(t)> => (value t v) (where len = ||v||)
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val(bool) ::= 0x00 => false
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| 0x01 => true
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val(u8) ::= v:<core:byte> => (u8 v)
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val(s8) ::= v:<core:byte> => (s8 v) if v < 128 else (v - 256)
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val(s16) ::= v:<core:s16> => (s16 v)
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val(u16) ::= v:<core:u16> => (u16 v)
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val(s32) ::= v:<core:s32> => (s32 v)
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val(u32) ::= v:<core:u32> => (u32 v)
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val(s64) ::= v:<core:s64> => (s64 v)
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val(u64) ::= v:<core:u64> => (u64 v)
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val(f32) ::= v:<core:f32> => (f32 v) (if !isnan(v))
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| 0x00 0x00 0xC0 0x7F => (f32 nan)
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val(f64) ::= v:<core:f64> => (f64 v) (if !isnan(v))
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| 0x00 0x00 0x00 0x00 0x00 0x00 0xF8 0x7F => (f64 nan)
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val(char) ::= v:<core:u32> => v (if v < 0xD800 or 0xE000 <= v <= 0x10FFFF)
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val(string) ::= v:<core:name> => v
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val(i:<typeidx>) ::= v:<val(type-index-space[i])> => v
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val((record (field l t)+)) ::= v+:<val(t)>+ => (record v+)
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val((variant (case l t?)+) ::= i:<core:u32> v?:<val(t[i])>? => (variant l[i] v?)
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val((list t)) ::= v:vec(<val(t)>) => (list v)
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val((tuple t+)) ::= v+:<val(t)>+ => (tuple v+)
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val((flags l+)) ::= (v:<core:byte>)^N => (flags (l[i] for i in 0..N-1 if v & 2^i > 0)) (where N = ceil(|l+| / 8))
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val((enum l+)) ::= i:<core:u32> => (enum l[i])
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val((option t)) ::= 0x00 => none
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| 0x01 v:<val(t)> => (some v)
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val((result)) ::= 0x00 => ok
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| 0x01 => error
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val((result t)) ::= 0x00 v:<val(t)> => (ok v)
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| 0x01 => error
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val((result (error u))) ::= 0x00 => ok
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| 0x01 v:<val(u)> => (error v)
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val((result t (error u))) ::= 0x00 v:<val(t)> => (ok v)
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| 0x01 v:<val(u)> => (error v)
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value ::= t:<valtype> len:<uN> v:<val(t)> => (value t v) (where len = ||v||)
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val(bool) ::= 0x00 => false
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| 0x01 => true
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val(u8) ::= v:<core:byte> => (u8 v)
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val(s8) ::= v:<core:byte> => (s8 v) if v < 128 else (v - 256)
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val(s16) ::= v:<core:s16> => (s16 v)
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val(u16) ::= v:<core:u16> => (u16 v)
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val(s32) ::= v:<core:s32> => (s32 v)
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val(u32) ::= v:<core:u32> => (u32 v)
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val(s64) ::= v:<core:s64> => (s64 v)
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val(u64) ::= v:<core:u64> => (u64 v)
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val(f32) ::= v:<core:f32> => (f32 v) (if !isnan(v))
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| 0x00 0x00 0xC0 0x7F => (f32 nan)
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val(f64) ::= v:<core:f64> => (f64 v) (if !isnan(v))
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| 0x00 0x00 0x00 0x00 0x00 0x00 0xF8 0x7F => (f64 nan)
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val(char) ::= v:<core:u32> => v (if v < 0xD800 or 0xE000 <= v <= 0x10FFFF)
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val(string) ::= v:<core:name> => v
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val(i:<typeidx>) ::= v:<val(type-index-space[i])> => v
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val((record (field l t)+)) ::= v+:<val(t)>+ => (record v+)
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val((variant (case l t?)+) ::= a:<core:byte> v?:<val(t[i])>? => (variant l[a] v?) (if |l| <= 255)
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| a:<core:byte> b:<core:byte> v?:<val(t[i])>? => (variant l[a | b << 8] v?) (if |l| <= 65535)
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| a:<core:byte> b:<core:byte> c:<core:byte> v?:<val(t[i])>? => (variant l[a | b << 8 | c << 16] v?) (if |l| <= 16777215)
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| a:<core:byte> b:<core:byte> c:<core:byte> d:<core:byte> v?:<val(t[i])>? => (variant l[a | b << 8 | c << 16 | d << 24] v?) (if |l| > 16777215)
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val((list t)) ::= v:vec(<val(t)>) => (list v)
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val((tuple t+)) ::= v+:<val(t)>+ => (tuple v+)
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val((flags l+)) ::= (v:<core:byte>)^N => (flags (l[i] for i in 0..N-1 if v & 2^i > 0)) (where N = ceil(|l+| / 8))
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val((enum l+)) ::= a:<core:byte> => (enum l[a]) (if |l| <= 255)
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| a:<core:byte> b:<core:byte> => (enum l[a | b << 8]) (if |l| <= 65535)
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| a:<core:byte> b:<core:byte> c:<core:byte> => (enum l[a | b << 8 | c << 16]) (if |l| <= 16777215)
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| a:<core:byte> b:<core:byte> c:<core:byte> d:<core:byte> => (enum l[a | b << 8 | c << 16 | d << 24]) (if |l| > 16777215)
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val((option t)) ::= 0x00 => none
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| 0x01 v:<val(t)> => (some v)
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val((result)) ::= 0x00 => ok
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| 0x01 => error
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val((result t)) ::= 0x00 v:<val(t)> => (ok v)
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| 0x01 => error
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val((result (error u))) ::= 0x00 => ok
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| 0x01 v:<val(u)> => (error v)
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val((result t (error u))) ::= 0x00 v:<val(t)> => (ok v)
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| 0x01 v:<val(u)> => (error v)
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```
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Notes:
@@ -408,7 +414,9 @@ Notes:
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- [`core:uN`]
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- [`core:f32`]
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- [`core:f64`]
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* `|` operator is used to denote bitwise OR operation, which performs OR on every bit of two numbers in their binary form
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* `&` operator is used to denote bitwise AND operation, which performs AND on every bit of two numbers in their binary form
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* `<<` operator is used to denote a bitwise left shift operation, which appends `0` at LSB position
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* `isnan` is a function, which takes a floating point number as a parameter and returns `true` iff it represents a NaN as defined in [IEEE 754 standard]
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* `||B||` is the length of the byte sequence generated from the production `B` in a derivation as defined in [Core convention auxilary notation]
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