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preserves
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Tony Garnock-Jones 2019-10-09 15:58:02 +01:00
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40
canonical-binary.md
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@ -21,41 +21,19 @@ This document specifies canonical form for the Preserves compact
binary syntax.
**General rules.**
Streaming formats ("format C") MUST NOT be used.
Annotations MUST NOT be present.
Placeholders MUST NOT be used.
Where possible, fixed-length ("format A") MUST be used in preference
Streaming formats ("format C") *MUST NOT* be used.
Annotations *MUST NOT* be present.
Placeholders *MUST NOT* be used.
Where possible, fixed-length ("format A") *MUST* be used in preference
to variable-length ("format B") formats.
**Signed integers.**
When a `SignedInteger` *n* is greater than or equal to -3 and less
than 13 (i.e. -3≤*n*<13), it MUST be represented using the single-byte
encoding with initial nibble equal to 3.
Otherwise (i.e. when *n*<-3 or *n*≥13), it MUST be represented using
the multi-byte encoding with initial nibble equal to 4, and the
variable-length part must be as short as
possible.[^signed-integer-examples]
[^signed-integer-examples]: The following examples from
[the specification][spec] are all in canonical form:
[[ -257 ]] = 42 FE FF [[ -3 ]] = 3D [[ 128 ]] = 42 00 80
[[ -256 ]] = 42 FF 00 [[ -2 ]] = 3E [[ 255 ]] = 42 00 FF
[[ -255 ]] = 42 FF 01 [[ -1 ]] = 3F [[ 256 ]] = 42 01 00
[[ -254 ]] = 42 FF 02 [[ 0 ]] = 30 [[ 32767 ]] = 42 7F FF
[[ -129 ]] = 42 FF 7F [[ 1 ]] = 31 [[ 32768 ]] = 43 00 80 00
[[ -128 ]] = 41 80 [[ 12 ]] = 3C [[ 65535 ]] = 43 00 FF FF
[[ -127 ]] = 41 81 [[ 13 ]] = 41 0D [[ 65536 ]] = 43 01 00 00
[[ -4 ]] = 41 FC [[ 127 ]] = 41 7F [[ 131072 ]] = 43 02 00 00
**Sets.**
The elements of a `Set` MUST be serialized sorted in ascending order
The elements of a `Set` *MUST* be serialized sorted in ascending order
following the total order relation defined in the
[Preserves specification][spec].
**Dictionaries.**
The key-value pairs in a `Dictionary` MUST be serialized sorted in
The key-value pairs in a `Dictionary` *MUST* be serialized sorted in
ascending order by key, following the total order relation defined in
the [Preserves specification][spec].[^no-need-for-by-value]
@ -63,9 +41,9 @@ the [Preserves specification][spec].[^no-need-for-by-value]
pair, since a `Dictionary` has no duplicate keys.
**Other kinds of `Value`.**
There are no special canonicalization restrictions on `String`s,
`ByteString`s, `Symbol`s, `Boolean`s, `Float`s, `Double`s, `Record`s,
or `Sequence`s.
There are no special canonicalization restrictions on
`SignedInteger`s, `String`s, `ByteString`s, `Symbol`s, `Boolean`s,
`Float`s, `Double`s, `Record`s, or `Sequence`s.
<!-- Heading to visually offset the footnotes from the main document: -->
## Notes

3
preserves.md
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@ -649,7 +649,8 @@ Integers in the range [-3,12] are compactly represented using format A
because they are so frequently used. Other integers are represented
using format B.
Format C *MUST NOT* be used for `SignedInteger`s.
Format C *MUST NOT* be used for `SignedInteger`s. Format A *MUST* be
used for integers in the range -3 to 12, inclusive.
The function `intbytes(x)` gives the big-endian two's-complement
binary representation of `x`, taking exactly as many whole bytes as