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String mapi ~2.5x perf improvement (v2) #9482

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Merged
merged 10 commits into from
Jul 25, 2020
Merged

String mapi ~2.5x perf improvement (v2) #9482

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c777c6a
Move `String.length` to the top of its module so that the `length` fu…
abelbraaksma Jun 17, 2020
3a91ebc
Using known length for mapping, and unrolling x2 to improve perf of S…
abelbraaksma Jun 17, 2020
3744f53
Fix two unapparent errors in the unroll loop, fix nit on parens
abelbraaksma Jun 18, 2020
4d15697
Add String.mapi tests for all new unrolling corner cases, and some ge…
abelbraaksma Jun 18, 2020
2522538
Add side-effect test, this would fail if sequentiality of String.mapi…
abelbraaksma Jun 18, 2020
82a2040
Remove "foo" from tests
abelbraaksma Jun 19, 2020
3936ad0
Remove unrolling of loop in String.mapi
abelbraaksma Jun 19, 2020
eabc956
Merge branch 'master' into String.mapi-perf
cartermp Jun 27, 2020
cab4dbd
Merge with 'master'
abelbraaksma Jul 11, 2020
4a0420a
Merge branch 'String.mapi-perf' of https://github.com/abelbraaksma/fs…
abelbraaksma Jul 11, 2020
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14 changes: 10 additions & 4 deletions src/fsharp/FSharp.Core/string.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,13 +52,19 @@ namespace Microsoft.FSharp.Core

[<CompiledName("MapIndexed")>]
let mapi (mapping: int -> char -> char) (str:string) =
if String.IsNullOrEmpty str then
let len = length str
if len = 0 then
String.Empty
else
let res = StringBuilder str.Length
let result = str.ToCharArray()
let f = OptimizedClosures.FSharpFunc<_,_,_>.Adapt(mapping)
str |> iteri (fun i c -> res.Append(f.Invoke(i, c)) |> ignore)
res.ToString()

let mutable i = 0
while i < len do
result.[i] <- f.Invoke(i, result.[i])
i <- i + 1

new String(result)

[<CompiledName("Filter")>]
let filter (predicate: char -> bool) (str:string) =
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32 changes: 28 additions & 4 deletions tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Collections/StringModule.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -103,11 +103,35 @@ type StringModule() =

[<Test>]
member this.MapI() =
let e1 = String.mapi (fun i c -> char(int c + i)) "foo"
Assert.AreEqual("fpq", e1)
let e1 = String.mapi (fun _ c -> c) "12345"
Assert.AreEqual("12345", e1)

let e2 = String.mapi (fun i c -> c) null
Assert.AreEqual("", e2)
let e2 = String.mapi (fun _ c -> c + char 1) "1"
Assert.AreEqual("2", e2)

let e3 = String.mapi (fun _ c -> c + char 1) "AB"
Assert.AreEqual("BC", e3)

let e4 = String.mapi (fun i c -> char(int c + i)) "hello"
Assert.AreEqual("hfnos", e4)

let e5 = String.mapi (fun _ c -> c) null
Assert.AreEqual("", e5)

let e6 = String.mapi (fun _ c -> c) String.Empty
Assert.AreEqual("", e6)

let e7 = String.mapi (fun _ _ -> failwith "should not fail") null
Assert.AreEqual("", e7)

let e8 = String.mapi (fun i _ -> if i = 1 then failwith "should not fail" else char i) "X"
Assert.AreEqual("\u0000", e8)

// side-effect and "order of operation" test
let mutable x = 0
let e9 = String.mapi (fun i c -> x <- x + i; c + char x) "abcde"
Assert.AreEqual(x, 10)
Assert.AreEqual(e9, "acfjo")

[<Test>]
member this.Filter() =
Expand Down