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Optimize String.escaped #1637

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merged 8 commits into from Feb 28, 2018
Merged

Optimize String.escaped #1637

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d25eaa6
Optimize String.escaped
nojb Feb 27, 2018
b2be212
Use functional style
nojb Feb 27, 2018
5c7b441
Simplify
nojb Feb 27, 2018
e92ed4e
Fix
nojb Feb 27, 2018
3cfb0bf
Avoid branch in String.escaped
nojb Feb 28, 2018
35a7521
Use local function
nojb Feb 28, 2018
996b0ea
Use more descriptive name for local function
nojb Feb 28, 2018
bed0aec
Changes
nojb Feb 28, 2018
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18 changes: 10 additions & 8 deletions stdlib/string.ml
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Expand Up @@ -100,15 +100,17 @@ let trim s =
then bts (B.trim (bos s))
else s

let escaped s =
let rec needs_escape i =
if i >= length s then false else
match unsafe_get s i with
| '\"' | '\\' | '\n' | '\t' | '\r' | '\b' -> true
| ' ' .. '~' -> needs_escape (i+1)
| _ -> true
let needs_escape s =
let rec aux s n i =
if i >= n then false else
match String.unsafe_get s i with
| '\"' | '\\' | '\000'..'\031' | '\127'.. '\255' -> true
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Side note: it is "tempting" to drop the check on the length altogether (also avoiding the need to compute the length), relying on the fact that String.unsafe_get s (String.length s) returns \000. The trouble, in addition to stressing @xavierleroy, is that this doesn't work with js_of_ocaml (and presumably Bucklescript).

| _ -> aux s n (i+1)
in
if needs_escape 0 then
aux s (String.length s) 0

let escaped s =
if needs_escape s then
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On second thought (sorry), the code could be simplified by directly calling from escaped the recursive function (with the three arguments). It probably improves even a bit the generated bytecode.

bts (B.escaped (bos s))
else
s
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