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ncodeunits(c::Char): fast equivalent of ncodeunits(string(c)) #29153

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Sep 14, 2018
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ncodeunits(c::Char): fast equivalent of ncodeunits(string(c)) #29153

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59dba6f
base/char.jl: tweak doc strings
StefanKarpinski Sep 12, 2018
d4d577e
define ncodeunits(c::Char) as fast equivalent of ncodeunits(string(c))
StefanKarpinski Sep 12, 2018
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50 changes: 29 additions & 21 deletions base/char.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

"""
The `AbstractChar` type is the supertype of all character implementations
in Julia. A character represents a Unicode code point, and can be converted
in Julia. A character represents a Unicode code point, and can be converted
to an integer via the [`codepoint`](@ref) function in order to obtain the
numerical value of the code point, or constructed from the same integer.
These numerical values determine how characters are compared with `<` and `==`,
Expand All @@ -11,7 +11,7 @@ method and a `T(::UInt32)` constructor, at minimum.

A given `AbstractChar` subtype may be capable of representing only a subset
of Unicode, in which case conversion from an unsupported `UInt32` value
may throw an error. Conversely, the built-in [`Char`](@ref) type represents
may throw an error. Conversely, the built-in [`Char`](@ref) type represents
a *superset* of Unicode (in order to losslessly encode invalid byte streams),
in which case conversion of a non-Unicode value *to* `UInt32` throws an error.
The [`isvalid`](@ref) function can be used to check which codepoints are
Expand All @@ -34,7 +34,7 @@ AbstractChar
Char(c::Union{Number,AbstractChar})

`Char` is a 32-bit [`AbstractChar`](@ref) type that is the default representation
of characters in Julia. `Char` is the type used for character literals like `'x'`
of characters in Julia. `Char` is the type used for character literals like `'x'`
and it is also the element type of [`String`](@ref).

In order to losslessly represent arbitrary byte streams stored in a `String`,
Expand All @@ -50,18 +50,27 @@ Char
(::Type{T})(x::AbstractChar) where {T<:Union{Number,AbstractChar}} = T(codepoint(x))
(::Type{T})(x::T) where {T<:AbstractChar} = x

codepoint(c::Char) = UInt32(c)
"""
ncodeunits(c::Char) -> Int

Return the number of code units required to encode a character as UTF-8.
This is the number of bytes which will be printed if the character is written
to an output stream, or `ncodeunits(string(c))` but computed efficiently.
"""
codepoint(c::AbstractChar)
ncodeunits(c::Char) = write(devnull, c) # this is surprisingly efficient

"""
codepoint(c::AbstractChar) -> Integer

Return the Unicode codepoint (an unsigned integer) corresponding
to the character `c` (or throw an exception if `c` does not represent
a valid character). For `Char`, this is a `UInt32` value, but
a valid character). For `Char`, this is a `UInt32` value, but
`AbstractChar` types that represent only a subset of Unicode may
return a different-sized integer (e.g. `UInt8`).
"""
codepoint # defined for Char in boot.jl
function codepoint end

codepoint(c::Char) = UInt32(c)

struct InvalidCharError{T<:AbstractChar} <: Exception
char::T
Expand Down Expand Up @@ -91,7 +100,7 @@ end
# not to support malformed or overlong encodings.

"""
ismalformed(c::AbstractChar)
ismalformed(c::AbstractChar) -> Bool
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Are we still using this syntax or are we transitioning to ismalformed(c::AbstractChar)::Bool in documentation?

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As far as I'm aware we're still using this syntax most places.


Return `true` if `c` represents malformed (non-Unicode) data according to the
encoding used by `c`. Defaults to `false` for non-`Char` types. See also
Expand All @@ -100,9 +109,9 @@ encoding used by `c`. Defaults to `false` for non-`Char` types. See also
ismalformed(c::AbstractChar) = false

"""
isoverlong(c::AbstractChar)
isoverlong(c::AbstractChar) -> Bool

Return `true` if `c` represents an overlong UTF-8 sequence. Defaults
Return `true` if `c` represents an overlong UTF-8 sequence. Defaults
to `false` for non-`Char` types. See also [`decode_overlong`](@ref)
and [`show_invalid`](@ref).
"""
Expand All @@ -123,6 +132,15 @@ function UInt32(c::Char)
((u & 0x007f0000) >> 4) | ((u & 0x7f000000) >> 6)
end

"""
decode_overlong(c::AbstractChar) -> Integer

When [`isoverlong(c)`](@ref) is `true`, `decode_overlong(c)` returns
the Unicode codepoint value of `c`. `AbstractChar` implementations
that support overlong encodings should implement `Base.decode_overlong`.
"""
function decode_overlong end

function decode_overlong(c::Char)
u = reinterpret(UInt32, c)
l1 = leading_ones(u)
Expand All @@ -133,15 +151,6 @@ function decode_overlong(c::Char)
((u & 0x007f0000) >> 4) | ((u & 0x7f000000) >> 6)
end

"""
decode_overlong(c::AbstractChar)

When [`isoverlong(c)`](@ref) is `true`, `decode_overlong(c)` returns
the Unicode codepoint value of `c`. `AbstractChar` implementations
that support overlong encodings should implement `Base.decode_overlong`.
"""
decode_overlong

function Char(u::UInt32)
u < 0x80 && return reinterpret(Char, u << 24)
u < 0x00200000 || code_point_err(u)::Union{}
Expand Down Expand Up @@ -197,7 +206,6 @@ hash(x::Char, h::UInt) =
hash_uint64(((reinterpret(UInt32, x) + UInt64(0xd4d64234)) << 32) ⊻ UInt64(h))

first_utf8_byte(c::Char) = (reinterpret(UInt32, c) >> 24) % UInt8
codelen(c::Char) = 4 - (trailing_zeros(0xff000000 | reinterpret(UInt32, c)) >> 3)

# fallbacks:
isless(x::AbstractChar, y::AbstractChar) = isless(Char(x), Char(y))
Expand Down Expand Up @@ -270,7 +278,7 @@ function show(io::IO, c::AbstractChar)
write(io, 0x27)
else # unprintable, well-formed, non-overlong Unicode
u = codepoint(c)
write(io, 0x27, 0x5c, c <= '\x7f' ? 0x78 : c <= '\uffff' ? 0x75 : 0x55)
write(io, 0x27, 0x5c, u <= 0x7f ? 0x78 : u <= 0xffff ? 0x75 : 0x55)
d = max(2, 8 - (leading_zeros(u) >> 2))
while 0 < d
write(io, hex_chars[((u >> ((d -= 1) << 2)) & 0xf) + 1])
Expand Down
2 changes: 1 addition & 1 deletion base/io.jl
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Expand Up @@ -974,7 +974,7 @@ function skipchars(predicate, io::IO; linecomment=nothing)
if c === linecomment
readline(io)
elseif !predicate(c)
skip(io, -codelen(c))
skip(io, -ncodeunits(c))
break
end
end
Expand Down
4 changes: 2 additions & 2 deletions base/strings/substring.jl
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Expand Up @@ -149,7 +149,7 @@ function string(a::Union{Char, String, SubString{String}}...)
n = 0
for v in a
if v isa Char
n += codelen(v)
n += ncodeunits(v)
else
n += sizeof(v)
end
Expand All @@ -159,7 +159,7 @@ function string(a::Union{Char, String, SubString{String}}...)
for v in a
if v isa Char
x = bswap(reinterpret(UInt32, v))
for j in 1:codelen(v)
for j in 1:ncodeunits(v)
unsafe_store!(pointer(out, offs), x % UInt8)
offs += 1
x >>= 8
Expand Down
23 changes: 23 additions & 0 deletions test/char.jl
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Expand Up @@ -256,3 +256,26 @@ Base.codepoint(c::ASCIIChar) = reinterpret(UInt8, c)
@test_throws MethodError write(IOBuffer(), ASCIIChar('x'))
@test_throws MethodError read(IOBuffer('x'), ASCIIChar)
end

@testset "ncodeunits(::Char)" begin
# valid encodings
@test ncodeunits('\0') == 1
@test ncodeunits('\x1') == 1
@test ncodeunits('\x7f') == 1
@test ncodeunits('\u80') == 2
@test ncodeunits('\uff') == 2
@test ncodeunits('\u7ff') == 2
@test ncodeunits('\u800') == 3
@test ncodeunits('\uffff') == 3
@test ncodeunits('\U10000') == 4
@test ncodeunits('\U10ffff') == 4
# invalid encodings
@test ncodeunits(reinterpret(Char, 0x80_00_00_00)) == 1
@test ncodeunits(reinterpret(Char, 0x81_00_00_00)) == 1
@test ncodeunits(reinterpret(Char, 0x80_80_00_00)) == 2
@test ncodeunits(reinterpret(Char, 0x80_01_00_00)) == 2
@test ncodeunits(reinterpret(Char, 0x80_00_80_00)) == 3
@test ncodeunits(reinterpret(Char, 0x80_00_01_00)) == 3
@test ncodeunits(reinterpret(Char, 0x80_00_00_80)) == 4
@test ncodeunits(reinterpret(Char, 0x80_00_00_01)) == 4
end
4 changes: 2 additions & 2 deletions test/iostream.jl
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Expand Up @@ -30,9 +30,9 @@
@test read(file, Char) == 'n'

# test it correctly handles unicode
for (byte,char) in zip(1:4, ('@','߷','࿊','𐋺'))
for (byte, char) in zip(1:4, ('@','߷','࿊','𐋺'))
append_to_file("abcdef$char")
@test Base.codelen(char) == byte
@test ncodeunits(char) == byte
@test !eof(skipchars(isletter, file))
@test read(file, Char) == char
end
Expand Down