note
	description: "Eiffel implementations for Unicode encoding conversion."
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date: 2020-05-20 11:14:50 +0000 (Wed, 20 May 2020) $"
	revision: "$Revision: 104299 $"

class 
	UNICODE_CONVERSION

create {ENCODING}
	default_create

feature {NONE} -- Initialization

	default_create
			-- Process instances of classes with no creation clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end
	
feature {ENCODING} -- Access

	last_converted_stream: STRING_8
			-- Stream prepresentation of last converted string.
			-- (from ENCODING_I)
		require -- from ENCODING_I
			last_conversion_successful: last_conversion_successful
		do
			check
				from_precondition: attached last_converted_string as l_last
			then
				if last_was_wide_string then
					Result := string_16_to_stream (l_last.as_string_32)
				else
					Result := string_general_to_stream (l_last)
				end
			end
		ensure -- from ENCODING_I
			last_converted_stream_not_void: Result /= Void
		end

	last_converted_string: detachable READABLE_STRING_GENERAL
			-- Last converted string.
			-- (from ENCODING_I)

	last_converted_string_8: STRING_8
			-- (from ENCODING_I)
		require -- from ENCODING_I
			last_conversion_successful: last_conversion_successful
			not_wide: not last_was_wide_string
		do
			check
					attached last_converted_string as l_string
			then
				Result := string_general_to_stream (l_string)
			end
		ensure -- from ENCODING_I
			last_converted_stream_not_void: Result /= Void
		end
	
feature -- Access

	generating_type: TYPE [detachable UNICODE_CONVERSION]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generating_type_not_void: Result /= Void
		end

	generator: STRING_8
			-- Name of current object's generating class
			-- (base class of the type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generator_not_void: Result /= Void
			generator_not_empty: not Result.is_empty
		end
	
feature -- Comparison

	frozen deep_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void
			-- or attached to isomorphic object structures?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_deep_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			shallow_implies_deep: standard_equal (a, b) implies Result
			both_or_none_void: (a = Void) implies (Result = (b = Void))
			same_type: (Result and (a /= Void)) implies (b /= Void and then a.same_type (b))
			symmetric: Result implies deep_equal (b, a)
		end

	frozen equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached
			-- to objects considered equal?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.is_equal (b))
		end

	frozen is_deep_equal alias "≡≡≡" (other: UNICODE_CONVERSION): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			shallow_implies_deep: standard_is_equal (other) implies Result
			same_type: Result implies same_type (other)
			symmetric: Result implies other.is_deep_equal (Current)
		end

	is_equal (other: UNICODE_CONVERSION): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		end

	frozen standard_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached to
			-- field-by-field identical objects of the same type?
			-- Always uses default object comparison criterion.
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.standard_is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.standard_is_equal (b))
		end

	frozen standard_is_equal alias "≜" (other: UNICODE_CONVERSION): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object, and field-by-field identical to it?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
		end
	
feature {ENCODING} -- Status report

	is_code_page_convertable (a_from_code_page, a_to_code_page: READABLE_STRING_8): BOOLEAN
		obsolete "Use is_code_page_convertible [2020-04-22]"
			-- Is a_from_code_page convertible to a_to_code_page.
			-- (from ENCODING_I)
		do
			Result := is_code_page_convertible (a_from_code_page, a_to_code_page)
		end

	last_conversion_successful: BOOLEAN
			-- Was last conversion successful?
			-- (from ENCODING_I)

	last_was_wide_string: BOOLEAN
			-- Last conversion result was wide string?
			-- (from ENCODING_I)
	
feature -- Status report

	conforms_to (other: ANY): BOOLEAN
			-- Does type of current object conform to type
			-- of other (as per Eiffel: The Language, chapter 13)?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		end

	same_type (other: ANY): BOOLEAN
			-- Is type of current object identical to type of other?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
		end
	
feature -- Conversion

	convert_to (a_from_code_page: READABLE_STRING_8; a_from_string: READABLE_STRING_GENERAL; a_to_code_page: READABLE_STRING_8)
			-- Convert between Unicode encodings.
		require -- from ENCODING_I
			a_from_code_page_valid: is_code_page_valid (a_from_code_page)
			a_to_code_page_valid: is_code_page_valid (a_to_code_page)
			code_page_convertible: is_code_page_convertible (a_from_code_page, a_to_code_page)
			a_from_string_not_void: a_from_string /= Void
		do
			reset
			if a_from_code_page.is_case_insensitive_equal (a_to_code_page) then
				last_conversion_successful := True
				if a_from_string.is_string_8 then
					last_converted_string := a_from_string.to_string_8
				else
					last_converted_string := a_from_string.as_string_32
				end
			else
				if a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf8) then
					last_converted_string := utf8_to_utf32 (if a_from_string.is_valid_as_string_8 then
							a_from_string.to_string_8
						else
							{UTF_CONVERTER}.utf_32_string_to_utf_8_string_8 (a_from_string)
						end)
					last_conversion_successful := True
				elseif a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32) then
					if a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf8) then
						last_converted_string := utf32_to_utf8 (a_from_string.as_string_32)
						last_conversion_successful := True
					elseif a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf16) then
						last_converted_string := utf32_to_utf16 (a_from_string.as_string_32)
						last_was_wide_string := True
						last_conversion_successful := True
					end
				elseif a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf16) then
					if a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32) then
						last_converted_string := utf16_to_utf32 (a_from_string.as_string_32)
						last_conversion_successful := True
					end
				end
			end
		ensure -- from ENCODING_I
			success_implies_not_void: last_conversion_successful implies last_converted_stream /= Void
			success_implies_not_void: last_conversion_successful implies last_converted_string /= Void
		end

	multi_byte_to_pointer (a_string: READABLE_STRING_8): MANAGED_POINTER
			-- Managed pointer of a_string.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_string_not_void: a_string /= Void
		do
			Result := (create {C_STRING}.make (a_string)).managed_data
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	pointer_to_multi_byte (a_multi_string: POINTER; a_count: INTEGER_32): STRING_8
			-- STRING_8 read from a_multi_string.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_multi_string_not_default: a_multi_string /= default_pointer
			a_count_non_negative: a_count >= 0
		local
			i: INTEGER_32
			l_managed_pointer: MANAGED_POINTER
		do
			create l_managed_pointer.share_from_pointer (a_multi_string, a_count)
			create Result.make (a_count)
			from
				i := 0
			until
				i >= a_count
			loop
				Result.append_code (l_managed_pointer.read_natural_8 (i).to_natural_32)
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	pointer_to_string_32 (a_w_string: POINTER; a_count: INTEGER_32): STRING_32
			-- STRING_32 read from a_w_string of a_count bytes.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_w_string_not_default: a_w_string /= default_pointer
			a_count_non_negative: a_count >= 0
		local
			i: INTEGER_32
			l_managed_pointer: MANAGED_POINTER
			l_size: INTEGER_32
		do
			create l_managed_pointer.share_from_pointer (a_w_string, a_count)
			l_size := a_count // 4
			create Result.make (l_size)
			from
				i := 0
			until
				i >= l_size
			loop
				if i * 4 <= a_count then
					Result.append_code (l_managed_pointer.read_natural_32 (i * 4))
				end
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	pointer_to_wide_string (a_w_string: POINTER; a_count: INTEGER_32): STRING_32
			-- STRING_32 read from a_w_string of a_count bytes.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_w_string_not_default: a_w_string /= default_pointer
			a_count_non_negative: a_count >= 0
		local
			i: INTEGER_32
			l_managed_pointer: MANAGED_POINTER
			l_size: INTEGER_32
		do
			create l_managed_pointer.share_from_pointer (a_w_string, a_count)
			l_size := (a_count + 1) // 2
			create Result.make (l_size)
			from
				i := 0
			until
				i >= l_size
			loop
				if i * 2 <= a_count then
					Result.append_code (l_managed_pointer.read_natural_16 (i * 2).to_natural_32)
				end
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	string_16_to_stream (a_string: STRING_32): STRING_8
			-- We use a_string as 2 bytes encoding string, the first two bytes are not used.
			-- in the endianness of the current platform.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_string_not_void: a_string /= Void
		local
			l_managed_pointer: MANAGED_POINTER
			i, l_count: INTEGER_32
		do
			l_managed_pointer := wide_string_to_pointer (a_string)
			create Result.make (l_managed_pointer.count)
			from
				i := 0
				l_count := l_managed_pointer.count - 2
			until
				i = l_count
			loop
				Result.append_character (l_managed_pointer.read_natural_8 (i).to_character_8)
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
			valid_count: Result.count = a_string.count * 2
		end

	string_32_to_multi_byte (a_string: STRING_32): STRING_8
			-- Byte stream of a_string in endianness of the current platform.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_string_not_void: a_string /= Void
		local
			i: INTEGER_32
			l_code: NATURAL_32
			l_count: INTEGER_32
			l_is_little_endian: BOOLEAN
		do
			l_count := a_string.count
			if l_count > 0 then
				create Result.make (l_count * 4)
				from
					i := 1
					l_is_little_endian := Is_little_endian
				until
					i > l_count
				loop
					l_code := a_string.code (i)
					if l_is_little_endian then
						Result.append_code (l_code & 255);
						Result.append_code (l_code & 65280 |>> 8);
						Result.append_code (l_code & 16711680 |>> 16);
						Result.append_code (l_code & 4278190080 |>> 24)
					else
						Result.append_code (l_code & 4278190080 |>> 24);
						Result.append_code (l_code & 16711680 |>> 16);
						Result.append_code (l_code & 65280 |>> 8);
						Result.append_code (l_code & 255)
					end
					i := i + 1
				end
			else
				create Result.make_empty
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	string_8_to_wide_string (a_w_string: STRING_8): STRING_32
			-- Interpret a_w_string as a sequence of 2-byte characters into a STRING_32
			-- in endianness of the current platform.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_w_string_not_void: a_w_string /= Void
		local
			i: INTEGER_32
			l_size, l_count: INTEGER_32
			l_is_little_endian: BOOLEAN
			l_code: NATURAL_32
		do
			l_count := a_w_string.count
			l_size := (l_count + 1) // 2
			l_is_little_endian := Is_little_endian
			create Result.make (l_size)
			from
				i := 1
			until
				i > l_count
			loop
				if i + 1 <= l_count then
					if l_is_little_endian then
						l_code := a_w_string.code (i) | (a_w_string.code (i + 1) |<< 8)
					else
						l_code := (a_w_string.code (i) |<< 8) | a_w_string.code (i + 1)
					end;
					Result.append_code (l_code)
				end
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	string_general_to_stream (a_string: READABLE_STRING_GENERAL): STRING_8
			-- Streamize a_string.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_string_not_void: a_string /= Void
		do
			if a_string.is_string_8 then
				Result := a_string.to_string_8
			else
				Result := string_32_to_multi_byte (a_string.as_string_32)
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	wide_string_to_pointer (a_string: READABLE_STRING_32): MANAGED_POINTER
			-- Managed pointer of a_string which is taken as
			-- 16bits string. High 16bits of characters of a_string are discarded.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_string_not_void: a_string /= Void
		local
			i, nb: INTEGER_32
		do
			nb := a_string.count
			create Result.make ((nb + 1) * 2)
			from
				i := 0
			until
				i = nb
			loop
				Result.put_natural_16 (a_string.code (i + 1).to_natural_16, i * 2)
				i := i + 1
			end;
			Result.put_natural_16 (0, i * 2)
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end
	
feature -- Duplication

	frozen clone (other: detachable ANY): like other
		obsolete "Use `twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- equal to other
			--
			-- For non-void other, clone calls copy;
			-- to change copying/cloning semantics, redefine copy.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.twin
			end
		ensure -- from ANY
			instance_free: class
			equal: Result ~ other
		end

	copy (other: UNICODE_CONVERSION)
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_equal: Current ~ other
		end

	frozen deep_clone (other: detachable ANY): like other
		obsolete "Use `deep_twin' instead. [2017-05-31]"
			-- Void if other is void: otherwise, new object structure
			-- recursively duplicated from the one attached to other
			-- (from ANY)
		do
			if other /= Void then
				Result := other.deep_twin
			end
		ensure -- from ANY
			instance_free: class
			deep_equal: deep_equal (other, Result)
		end

	frozen deep_copy (other: UNICODE_CONVERSION)
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		do
			copy (other.deep_twin)
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)
		end

	frozen deep_twin: UNICODE_CONVERSION
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)
		end

	frozen standard_clone (other: detachable ANY): like other
		obsolete "Use `standard_twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.standard_twin
			end
		ensure -- from ANY
			instance_free: class
			equal: standard_equal (Result, other)
		end

	frozen standard_copy (other: UNICODE_CONVERSION)
			-- Copy every field of other onto corresponding field
			-- of current object.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)
		end

	frozen standard_twin: UNICODE_CONVERSION
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)
		end

	frozen twin: UNICODE_CONVERSION
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
		end
	
feature -- Basic operations

	frozen as_attached: attached UNICODE_CONVERSION
		obsolete "Remove calls to this feature. [2017-05-31]"
			-- Attached version of Current.
			-- (Can be used during transitional period to convert
			-- non-void-safe classes to void-safe ones.)
			-- (from ANY)
		do
			Result := Current
		end

	frozen default: detachable UNICODE_CONVERSION
			-- Default value of object's type
			-- (from ANY)
		do
		end

	frozen default_pointer: POINTER
			-- Default value of type POINTER
			-- (Avoid the need to write p.default for
			-- some p of type POINTER.)
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end

	default_rescue
			-- Process exception for routines with no Rescue clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end
	
feature {NONE} -- Implementation

	Unicode_encodings: STRING_TABLE [READABLE_STRING_8]
			-- Supported Unicode encodings.
		once
			create Result.make (8);
			Result.put ({CODE_PAGE_CONSTANTS}.utf7, {CODE_PAGE_CONSTANTS}.utf7);
			Result.put ({CODE_PAGE_CONSTANTS}.utf8, {CODE_PAGE_CONSTANTS}.utf8);
			Result.put ({CODE_PAGE_CONSTANTS}.utf16, {CODE_PAGE_CONSTANTS}.utf16);
			Result.put ({CODE_PAGE_CONSTANTS}.utf16_le, {CODE_PAGE_CONSTANTS}.utf16_le);
			Result.put ({CODE_PAGE_CONSTANTS}.utf32, {CODE_PAGE_CONSTANTS}.utf32);
			Result.put ({CODE_PAGE_CONSTANTS}.utf32_le, {CODE_PAGE_CONSTANTS}.utf32_le);
			Result.put ({CODE_PAGE_CONSTANTS}.utf16_be, {CODE_PAGE_CONSTANTS}.utf16_be);
			Result.put ({CODE_PAGE_CONSTANTS}.utf32_be, {CODE_PAGE_CONSTANTS}.utf32_be)
		end
	
feature -- Endian

	Is_little_endian: BOOLEAN
			-- Is this system little endian?
			-- (from ENCODING_HELPER)
		once
			Result := {PLATFORM}.is_little_endian
		ensure -- from ENCODING_HELPER
			instance_free: class
		end

	string_16_switch_endian (a_str: STRING_32): STRING_32
			-- Switch endian of a_str for low bits.
			-- High bits are cleaned.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_str_not_void: a_str /= Void
		local
			l_code: NATURAL_32
			i, l_count: INTEGER_32
		do
			l_count := a_str.count
			create Result.make (l_count)
			from
				i := 1
			until
				i > l_count
			loop
				l_code := a_str.code (i);
				Result.append_code (l_code & 255 |<< 8 & 65280 + l_code & 65280 |>> 8 & 255)
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end

	string_32_switch_endian (a_str: STRING_32): STRING_32
			-- Switch endian of a_str for both high and low bits.
			-- (from ENCODING_HELPER)
		require -- from ENCODING_HELPER
			a_str_not_void: a_str /= Void
		local
			l_code: NATURAL_32
			i, l_count: INTEGER_32
		do
			l_count := a_str.count
			create Result.make (l_count)
			from
				i := 1
			until
				i > l_count
			loop
				l_code := a_str.code (i);
				Result.append_code (l_code & 255 |<< 24 & 4278190080 + l_code & 65280 |<< 8 + l_code & 16711680 |>> 8 + l_code & 4278190080 |>> 24 & 255)
				i := i + 1
			end
		ensure -- from ENCODING_HELPER
			instance_free: class
			result_not_void: Result /= Void
		end
	
feature -- Explicit Conversion

	append_code_point_to_utf8 (a_code: NATURAL_32; a_string: STRING_8)
			-- Append a Unicode code point a_code to a UTF-8 stream.
		require
			a_string_not_void: a_string /= Void
			a_code_is_valid: a_code >= 0 and then a_code <= 1114111
		do
			{UTF_CONVERTER}.utf_32_code_into_utf_8_string_8 (a_code, a_string)
		ensure
			a_string_appended: (a_code <= 127 implies a_string.count = old a_string.count + 1) and ((a_code > 127 and a_code <= 2047) implies a_string.count = old a_string.count + 2) and ((a_code > 2047 and a_code <= 65535) implies a_string.count = old a_string.count + 3) and ((a_code > 65535 and a_code <= 1114111) implies a_string.count = old a_string.count + 4)
		end

	read_character_from_utf8 (a_position: INTEGER_32; a_read_bytes: detachable INTEGER_32_REF; a_string: READABLE_STRING_8): CHARACTER_32
			-- Read a Unicode character from UTF-8 string.
			-- a_string is in UTF-8.
			-- a_position is the starting byte point of a character.
			-- a_read_bytes is the number of bytes read.
		require
			a_string_not_void: a_string /= Void
			a_position_in_range: a_position > 0 and a_position <= a_string.count
			a_position_valid: a_string.code (a_position).to_natural_8 <= 127 or (a_string.code (a_position).to_natural_8 & 224) = 192 or (a_string.code (a_position).to_natural_8 & 240) = 224 or (a_string.code (a_position).to_natural_8 & 248) = 240 or (a_string.code (a_position).to_natural_8 & 252) = 248 or (a_string.code (a_position).to_natural_8 & 254) = 252
		local
			l_pos: INTEGER_32
			l_nat8: NATURAL_8
			l_code: NATURAL_32
		do
			l_pos := a_position
			l_nat8 := a_string.code (l_pos).to_natural_8
			if l_nat8 <= 127 then
				Result := l_nat8.to_character_32
			elseif (l_nat8 & 224) = 192 then
				l_code := (l_nat8 & 31).to_natural_32 |<< 6
				l_pos := l_pos + 1
				l_nat8 := a_string.code (l_pos).to_natural_8
				l_code := l_code | (l_nat8 & 63).to_natural_32
				Result := l_code.to_character_32
			elseif (l_nat8 & 240) = 224 then
				l_code := (l_nat8 & 15).to_natural_32 |<< 12
				l_nat8 := a_string.code (l_pos + 1).to_natural_8
				l_code := l_code | ((l_nat8 & 63).to_natural_32 |<< 6)
				l_nat8 := a_string.code (l_pos + 2).to_natural_8
				l_code := l_code | (l_nat8 & 63).to_natural_32
				Result := l_code.to_character_32
				l_pos := l_pos + 2
			elseif (l_nat8 & 248) = 240 then
				l_code := (l_nat8 & 7).to_natural_32 |<< 18
				l_nat8 := a_string.code (l_pos + 1).to_natural_8
				l_code := l_code | ((l_nat8 & 63).to_natural_32 |<< 12)
				l_nat8 := a_string.code (l_pos + 2).to_natural_8
				l_code := l_code | ((l_nat8 & 63).to_natural_32 |<< 6)
				l_nat8 := a_string.code (l_pos + 3).to_natural_8
				l_code := l_code | (l_nat8 & 63).to_natural_32
				Result := l_code.to_character_32
				l_pos := l_pos + 3
			elseif (l_nat8 & 252) = 248 then
				Result := ' '.to_character_32
				l_pos := l_pos + 4
			else
				Result := ' '.to_character_32
				l_pos := l_pos + 5
			end
			if a_read_bytes /= Void then
				a_read_bytes.set_item (l_pos - a_position + 1)
			end
		end

	utf16_to_utf32 (a_str: READABLE_STRING_32): STRING_32
			-- Convert utf16 to utf32.
		require
			a_str_not_void: a_str /= Void
		local
			i, l_count: INTEGER_32
			l_code: NATURAL_32
			l_temp: NATURAL_32
			l_lower: NATURAL_32
		do
			l_count := a_str.count
			create Result.make (l_count)
			from
				i := 1
			until
				i > l_count
			loop
				l_code := a_str.code (i)
				i := i + 1
				l_temp := l_code & 65535
				if i <= l_count then
					l_lower := a_str.code (i) & 65535
				end
				if l_temp >= 55296 and then l_temp <= 56319 and then i <= l_count and then l_lower >= 56320 and then l_lower <= 57343 then
					Result.append_code ((l_temp & 1023) |<< 10 + l_lower & 1023 + 65536)
					i := i + 1
				else
					Result.append_code (l_temp)
				end
			end
		ensure
			instance_free: class
			result_not_void: Result /= Void
		end

	utf32_to_utf16 (a_str: READABLE_STRING_32): STRING_32
			-- Convert utf32 to utf16 without data lose.
		require
			a_str_not_void: a_str /= Void
		local
			l_code: NATURAL_32
			i, l_count: INTEGER_32
		do
			create Result.make (a_str.count * 2)
			from
				i := 1
				l_count := a_str.count
			until
				i > l_count
			loop
				l_code := a_str.code (i) & 1048575
				if l_code > 65535 then
					l_code := l_code - 65536;
					Result.append_code (l_code |>> 10 | 55296);
					Result.append_code (l_code & 1023 | 56320)
				else
					Result.append_code (l_code)
				end
				i := i + 1
			end
		ensure
			instance_free: class
			result_not_void: Result /= Void
		end

	utf32_to_utf8 (a_string: READABLE_STRING_32): STRING_8
			-- Convert UTF32 to UTF8.
		require
			a_string_not_void: a_string /= Void
		do
			Result := {UTF_CONVERTER}.utf_32_string_to_utf_8_string_8 (a_string)
		ensure
			result_not_void: Result /= Void
		end

	utf8_to_utf32 (a_string: READABLE_STRING_8): STRING_32
			-- UTF8 to UTF32 conversion, Eiffel implementation.
		require
			a_string_not_void: a_string /= Void
		do
			Result := {UTF_CONVERTER}.utf_8_string_8_to_string_32 (a_string)
		ensure
			result_not_void: Result /= Void
		end
	
feature -- Output

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		once
			create Result;
			Result.set_output_default
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void
		end

	out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		do
			Result := tagged_out
		ensure -- from ANY
			out_not_void: Result /= Void
		end

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		local
			s: READABLE_STRING_8
		do
			if attached o then
				s := o.out
				if attached {READABLE_STRING_32} s as s32 then
					Io.put_string_32 (s32)
				elseif attached {READABLE_STRING_8} s as s8 then
					Io.put_string (s8)
				else
					Io.put_string_32 (s.as_string_32)
				end
			end
		ensure -- from ANY
			instance_free: class
		end

	frozen tagged_out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			tagged_out_not_void: Result /= Void
		end
	
feature -- Platform

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		once
			create Result
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
		end
	
feature -- Query

	is_code_page_convertible (a_from_code_page, a_to_code_page: READABLE_STRING_8): BOOLEAN
			-- Is a_from_code_page convertible to a_to_code_page.
		do
			Result := a_from_code_page = {CODE_PAGE_CONSTANTS}.utf8 and then a_to_code_page = {CODE_PAGE_CONSTANTS}.utf32
			if not Result then
				if a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf8) then
					Result := a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf8) or else a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32)
				elseif a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32) then
					Result := a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32) or else a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf8) or else a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf16)
				elseif a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf16) then
					Result := a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf16) or else a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf32)
				elseif a_from_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf7) then
					Result := a_to_code_page.is_case_insensitive_equal ({CODE_PAGE_CONSTANTS}.utf7)
				end
			end
		end

	is_code_page_valid (a_code_page: READABLE_STRING_8): BOOLEAN
			-- Is a_code_page valid?
		do
			if a_code_page /= Void and then not a_code_page.is_empty then
				Result := Unicode_encodings.has (a_code_page)
			end
		end

	is_valid_as_string_16 (a_string: READABLE_STRING_GENERAL): BOOLEAN
			-- Check high 16 bit of any char in a_string is zero.
		local
			i, nb: INTEGER_32
			l_area: SPECIAL [CHARACTER_32]
		do
			if a_string /= Void then
				if a_string.is_string_32 then
					from
						nb := a_string.count
						Result := True
						l_area := a_string.as_string_32.area
					until
						i = nb or not Result
					loop
						Result := l_area [i].code <= 65535
						i := i + 1
					end
				else
					Result := True
				end
			end
		end

	is_valid_utf8 (a_string: READABLE_STRING_8): BOOLEAN
			-- Is a_string valid UTF-8 string?
		require
			a_string_not_void: a_string /= Void
		do
			Result := {UTF_CONVERTER}.is_valid_utf_8_string_8 (a_string)
		end

	Last_conversion_lost_data: BOOLEAN = False
			-- Has last conversion between two encodings lost data?
	
feature {ENCODING} -- Reset

	reset
			-- Reset
			-- (from ENCODING_I)
		do
			last_converted_string := Void
			last_conversion_successful := False
			last_was_wide_string := False
		ensure -- from ENCODING_I
			last_converted_string_reset: last_converted_string = Void
			last_conversion_successful_reset: not last_conversion_successful
		end
	
feature {NONE} -- Retrieval

	frozen internal_correct_mismatch
			-- Called from runtime to perform a proper dynamic dispatch on correct_mismatch
			-- from MISMATCH_CORRECTOR.
			-- (from ANY)
		local
			l_msg: STRING_32
			l_exc: EXCEPTIONS
		do
			if attached {MISMATCH_CORRECTOR} Current as l_corrector then
				l_corrector.correct_mismatch
			else
				create l_msg.make_from_string ("Mismatch: ".as_string_32)
				create l_exc;
				l_msg.append (generating_type.name_32);
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
invariant
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

note
	library: "Encoding: Library of reusable components for Eiffel."
	copyright: "Copyright (c) 1984-2020, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	source: "[
		Eiffel Software
		5949 Hollister Ave., Goleta, CA 93117 USA
		Telephone 805-685-1006, Fax 805-685-6869
		Website http://www.eiffel.com
		Customer support http://support.eiffel.com
	]"

end -- class UNICODE_CONVERSION

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