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improve performance for materializing a string from a vector of Char #29551

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merged 2 commits into from
Oct 12, 2018
Merged

improve performance for materializing a string from a vector of Char #29551

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67de376
improve performance for materializing a string from a vector of Char
KristofferC Oct 7, 2018
a4c7169
fixup names from review
KristofferC Oct 7, 2018
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13 changes: 13 additions & 0 deletions base/strings/io.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -576,6 +576,19 @@ function unindent(str::AbstractString, indent::Int; tabwidth=8)
String(take!(buf))
end

function String(a::Vector{Char})
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Maybe the signature could be a::AbstractVector{Char}?

n = 0
for v in a
n += ncodeunits(v)
end
out = _string_n(n)
offs = 1
for v in a
offs += __string!(out, v, offs)
end
return out
end

function String(chars::AbstractVector{<:AbstractChar})
sprint(sizehint=length(chars)) do io
for c in chars
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34 changes: 23 additions & 11 deletions base/strings/substring.jl
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Expand Up @@ -145,6 +145,28 @@ end
string(a::String) = String(a)
string(a::SubString{String}) = String(a)

@inline function __string!(out, c::Char, offs::Integer)
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maybe name it __unsafe_string! to highlight the fact that it does not perform bounds checking?

x = bswap(reinterpret(UInt32, c))
n = ncodeunits(c)
unsafe_store!(pointer(out, offs), x % UInt8)
n == 1 && return n
x >>= 8
unsafe_store!(pointer(out, offs+1), x % UInt8)
n == 2 && return n
x >>= 8
unsafe_store!(pointer(out, offs+2), x % UInt8)
n == 3 && return n
x >>= 8
unsafe_store!(pointer(out, offs+3), x % UInt8)
return n
end

@inline function __string!(out, s::Union{String, SubString{String}}, offs::Integer)
n = sizeof(s)
unsafe_copyto!(pointer(out, offs), pointer(s), n)
return n
end

function string(a::Union{Char, String, SubString{String}}...)
n = 0
for v in a
Expand All @@ -157,17 +179,7 @@ function string(a::Union{Char, String, SubString{String}}...)
out = _string_n(n)
offs = 1
for v in a
if v isa Char
x = bswap(reinterpret(UInt32, v))
for j in 1:ncodeunits(v)
unsafe_store!(pointer(out, offs), x % UInt8)
offs += 1
x >>= 8
end
else
unsafe_copyto!(pointer(out,offs), pointer(v), sizeof(v))
offs += sizeof(v)
end
offs += __string!(out, v, offs)
end
return out
end
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