Add repeat for Char to fix performance of pow (JuliaLang#22797)

* Add repeat for Char to fix performance of pow * Address reviews * Update docstring
jeffwong · Jul 24, 2017 · 67f93bd · 67f93bd
1 parent 11547b0
commit 67f93bd
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Showing 6 changed files with 43 additions and 6 deletions.
diff --git a/base/strings/string.jl b/base/strings/string.jl
@@ -438,3 +438,25 @@ function repeat(s::String, r::Integer)
     end
     return out
 end
+
+"""
+    repeat(c::Char, r::Integer) -> String
+
+Repeat a character `r` times. This can equivalently be accomplished by calling [`c^r`](@ref ^).
+
+# Examples
+```jldoctest
+julia> repeat('A', 3)
+"AAA"
+```
+"""
+function repeat(c::Char, r::Integer)
+    if isascii(c)
+        r < 0 && throw(ArgumentError("can't repeat a character $r times"))
+        out = _string_n(r)
+        ccall(:memset, Ptr{Void}, (Ptr{UInt8}, Cint, Csize_t), out, c, r)
+        return out
+    else
+        return repeat(string(c), r)
+    end
+end
diff --git a/base/strings/types.jl b/base/strings/types.jl
@@ -152,6 +152,17 @@ reverseind(s::RevString, i::Integer) = endof(s) - i + 1
 reverseind(s::SubString{String}, i::Integer) =
     reverseind(s.string, nextind(s.string, endof(s.string))-s.offset-s.endof+i-1) - s.offset
 
+"""
+    repeat(s::AbstractString, r::Integer)
+
+Repeat a string `r` times. This can equivalently be accomplished by calling [`s^r`](@ref ^).
+
+# Examples
+```jldoctest
+julia> repeat("ha", 3)
+"hahaha"
+```
+"""
 function repeat(s::AbstractString, r::Integer)
     r <  0 ? throw(ArgumentError("can't repeat a string $r times")) :
     r == 0 ? "" :
@@ -160,9 +171,9 @@ function repeat(s::AbstractString, r::Integer)
 end
 
 """
-    ^(s::AbstractString, n::Integer)
+    ^(s::Union{AbstractString,Char}, n::Integer)
 
-Repeat `n` times the string `s`.
+Repeat a string or character `n` times.
 The [`repeat`](@ref) function is an alias to this operator.
 
 # Examples
@@ -171,7 +182,7 @@ julia> "Test "^3
 "Test Test Test "
 ```
 """
-(^)(s::AbstractString, r::Integer) = repeat(s,r)
+(^)(s::Union{AbstractString,Char}, r::Integer) = repeat(s,r)
 
 pointer(x::SubString{String}) = pointer(x.string) + x.offset
 pointer(x::SubString{String}, i::Integer) = pointer(x.string) + x.offset + (i-1)
diff --git a/doc/src/stdlib/arrays.md b/doc/src/stdlib/arrays.md
@@ -143,6 +143,7 @@ Base.cumsum_kbn
 Base.crc32c
 Base.LinAlg.diff
 Base.LinAlg.gradient
+Base.repeat(::AbstractArray)
 Base.rot180
 Base.rotl90
 Base.rotr90

diff --git a/doc/src/stdlib/linalg.md b/doc/src/stdlib/linalg.md
@@ -89,7 +89,6 @@ Base.inv(::AbstractMatrix)
 Base.LinAlg.pinv
 Base.LinAlg.nullspace
 Base.repmat
-Base.repeat
 Base.kron
 Base.SparseArrays.blkdiag
 Base.LinAlg.linreg

diff --git a/doc/src/stdlib/strings.md b/doc/src/stdlib/strings.md
@@ -6,6 +6,8 @@ Base.sizeof(::AbstractString)
 Base.:*(::AbstractString, ::Any...)
 Base.:^(::AbstractString, ::Integer)
 Base.string
+Base.repeat(::AbstractString, ::Integer)
+Base.repeat(::Char, ::Integer)
 Base.repr
 Core.String(::AbstractString)
 Base.transcode

diff --git a/test/strings/basic.jl b/test/strings/basic.jl
@@ -478,8 +478,10 @@ Base.endof(x::CharStr) = endof(x.chars)
 @test cmp(CharStr("\U1f596"), "\U1f596\U1f596") == -1
 
 # repeat function
-@test repeat("xx",3) == repeat("x",6) == "xxxxxx"
-@test repeat("αα",3) == repeat("α",6) == "αααααα"
+@test repeat("xx",3) == repeat("x",6) == repeat('x',6) == repeat(GenericString("x"), 6) == "xxxxxx"
+@test repeat("αα",3) == repeat("α",6) == repeat('α',6) == repeat(GenericString("α"), 6) == "αααααα"
+@test repeat("x",1) == repeat('x',1) == "x"^1 == 'x'^1 == GenericString("x")^1 == "x"
+@test repeat("x",0) == repeat('x',0) == "x"^0 == 'x'^0 == GenericString("x")^0 == ""
 
 # issue #12495: check that logical indexing attempt raises ArgumentError
 @test_throws ArgumentError "abc"[[true, false, true]]