From 975b92e5debe1fa25db4451a5c771494217a8bcf Mon Sep 17 00:00:00 2001
From: Lucas Bajolet <r4pass@hotmail.com>
Date: Tue, 15 Dec 2015 11:26:30 -0500
Subject: [PATCH] lib/json: Improved performance of Unicode-escaping in a
 `Text`

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
---
 lib/core/text/abstract_text.nit |   37 ++++++++++++++++++++++++-------------
 lib/json/static.nit             |   23 +++++++++++------------
 2 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/lib/core/text/abstract_text.nit b/lib/core/text/abstract_text.nit
index 1de1aa1..0b07edb 100644
--- a/lib/core/text/abstract_text.nit
+++ b/lib/core/text/abstract_text.nit
@@ -743,21 +743,32 @@ abstract class Text
 	#     assert "\\ud800\\udfd3".from_utf16_escape == '𐏓'
 	#     assert "\\u00e8".from_utf16_escape == 'è'
 	#     assert "\\u3042".from_utf16_escape == 'あ'
-	fun from_utf16_escape: Char do
-		var ln = length
-		if ln != 6 and ln != 12 then return 0xFFFD.code_point
-		var cphi = substring(2, 4).to_hex
-		if cphi < 0xD800 then return cphi.code_point
-		if cphi > 0xDFFF then return cphi.code_point
-		if cphi > 0xDBFF then return 0xFFFD.code_point
-		var cp = 0
-		cp += (cphi - 0xD800) << 10
-		var cplo = substring(8, 4).to_hex
+	fun from_utf16_escape(pos, ln: nullable Int): Char do
+		if pos == null then pos = 0
+		if ln == null then ln = length - pos
+		if ln < 6 then return 0xFFFD.code_point
+		var cp = from_utf16_digit(pos + 2)
+		if cp < 0xD800 then return cp.code_point
+		if cp > 0xDFFF then return cp.code_point
+		if cp > 0xDBFF then return 0xFFFD.code_point
+		if ln == 6 then return 0xFFFD.code_point
+		if ln < 12 then return 0xFFFD.code_point
+		cp <<= 16
+		cp += from_utf16_digit(pos + 8)
+		var cplo = cp & 0xFFFF
 		if cplo < 0xDC00 then return 0xFFFD.code_point
 		if cplo > 0xDFFF then return 0xFFFD.code_point
-		cp += cplo - 0xDC00
-		cp += 0x10000
-		return cp.code_point
+		return cp.from_utf16_surr.code_point
+	end
+
+	# Returns a UTF-16 escape value
+	#
+	#     var s = "\\ud800\\udfd3"
+	#     assert s.from_utf16_digit(2) == 0xD800
+	#     assert s.from_utf16_digit(8) == 0xDFD3
+	fun from_utf16_digit(pos: nullable Int): Int do
+		if pos == null then pos = 0
+		return to_hex(pos, 4)
 	end
 
 	# Encode `self` to percent (or URL) encoding
diff --git a/lib/json/static.nit b/lib/json/static.nit
index 15a4355..7c0e2cf 100644
--- a/lib/json/static.nit
+++ b/lib/json/static.nit
@@ -138,7 +138,8 @@ redef class Text
 	protected fun json_to_nit_string: String do
 		var res = new FlatBuffer.with_capacity(bytelen)
 		var i = 0
-		while i < self.length do
+		var ln = self.length
+		while i < ln do
 			var char = self[i]
 			if char == '\\' then
 				i += 1
@@ -154,21 +155,19 @@ redef class Text
 				else if char == 't' then
 					char = '\t'
 				else if char == 'u' then
-					var code = substring(i + 1, 4)
-					var hx = code.to_hex
-					if hx >= 0xD800 and hx <= 0xDFFF then
-						var lostr = substring(i + 7, 4)
-						if lostr.length < 4 then
-							hx = 0xFFFD
+					var u16_esc = from_utf16_digit(i + 1)
+					char = u16_esc.code_point
+					if char.is_surrogate and i + 10 < ln then
+						if self[i + 5] == '\\' and self[i + 6] == 'u' then
+							u16_esc <<= 16
+							u16_esc += from_utf16_digit(i + 7)
+							char = u16_esc.from_utf16_surr.code_point
+							i += 6
 						else
-							hx <<= 16
-							hx += lostr.to_hex
-							hx = hx.from_utf16_surr
+							char = 0xFFFD.code_point
 						end
-						i += 6
 					end
 					i += 4
-					char = hx.code_point
 				end
 				# `"`, `/` or `\` => Keep `char` as-is.
 			end
-- 
1.7.9.5