note
	description: "UTF-8 encoding routines"
	library: "Gobo Eiffel Kernel Library"
	copyright: "Copyright (c) 2001-2018, Eric Bezault and others"
	license: "MIT License"
	date: "$Date: 2019-02-07 22:54:15 +0000 (Thu, 07 Feb 2019) $"
	revision: "$Revision: 102807 $"

class interface
	UC_UTF8_ROUTINES

create 
	default_create
			-- Process instances of classes with no creation clause.
			-- (Default: do nothing.)
			-- (from ANY)

feature -- Access

	Any_: KL_ANY_ROUTINES
			-- Routines that ought to be in class ANY
			-- (from KL_IMPORTED_ANY_ROUTINES)
		ensure -- from KL_IMPORTED_ANY_ROUTINES
			instance_free: class
			any_routines_not_void: Result /= Void

	encoded_first_value (a_byte: CHARACTER_8): INTEGER_32
			-- Value encoded in first byte
		require
			is_encoded_first_byte: is_encoded_first_byte (a_byte)
		ensure
			instance_free: class
			value_positive: Result >= 0
			value_small_enough: Result < 128

	encoded_next_value (a_byte: CHARACTER_8): INTEGER_32
			-- Value encoded in one of the next bytes
		require
			is_encoded_next_byte: is_encoded_next_byte (a_byte)
		ensure
			instance_free: class
			value_positive: Result >= 0
			value_small_enough: Result < 64

	generating_type: TYPE [detachable UC_UTF8_ROUTINES]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		ensure -- from ANY
			generating_type_not_void: Result /= Void

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

	Integer_: KL_INTEGER_ROUTINES
			-- Routines that ought to be in class INTEGER
			-- (from KL_IMPORTED_INTEGER_ROUTINES)
		ensure -- from KL_IMPORTED_INTEGER_ROUTINES
			instance_free: class
			integer_routines_not_void: Result /= Void

	String_: KL_STRING_ROUTINES
			-- Routines that ought to be in class STRING
			-- (from KL_IMPORTED_STRING_ROUTINES)
		ensure -- from KL_IMPORTED_STRING_ROUTINES
			instance_free: class
			string_routines_not_void: Result /= Void

	Unicode: UC_UNICODE_ROUTINES
			-- Unicode routines
			-- (from UC_IMPORTED_UNICODE_ROUTINES)
		ensure -- from UC_IMPORTED_UNICODE_ROUTINES
			instance_free: class
			unicode_not_void: Result /= Void
	
feature -- Measurement

	character_byte_count (c: CHARACTER_8): INTEGER_32
			-- Number of bytes needed to encode character
			-- c with the UTF-8 encoding
		ensure
			instance_free: class
			character_byte_count_large_enough: Result >= 1
			character_byte_count_small_enough: Result <= 4

	code_byte_count (a_code: INTEGER_32): INTEGER_32
			-- Number of bytes needed to encode unicode character
			-- of code a_code with the UTF-8 encoding
		require
			valid_code: Unicode.valid_non_surrogate_code (a_code)
		ensure
			instance_free: class
			code_byte_count_large_enough: Result >= 1
			code_byte_count_small_enough: Result <= 4

	encoded_byte_count (a_byte: CHARACTER_8): INTEGER_32
			-- Number of bytes which were necessary to encode
			-- the unicode character whose first byte is a_byte
		require
			is_encoded_first_byte: is_encoded_first_byte (a_byte)
		ensure
			instance_free: class
			encoded_byte_code_large_enough: Result >= 1
			encoded_byte_code_small_enough: Result <= 4

	substring_byte_count (a_string: READABLE_STRING_GENERAL; start_index, end_index: INTEGER_32): INTEGER_32
			-- Number of bytes needed to encode characters  of
			-- a_string between start_index and end_index
			-- inclusive with the UTF-8 encoding
		require
			a_string_not_void: a_string /= Void
			valid_start_index: 1 <= start_index
			valid_end_index: end_index <= a_string.count
			meaningful_interval: start_index <= end_index + 1
		ensure
			instance_free: class
			substring_byte_count_positive: Result >= 0
	
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)
		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)

	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)
		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))

	frozen is_deep_equal (other: UC_UTF8_ROUTINES): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		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)

	is_equal (other: UC_UTF8_ROUTINES): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result

	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)
		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))

	frozen standard_is_equal (other: UC_UTF8_ROUTINES): 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
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
	
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

	is_encoded_first_byte (a_byte: CHARACTER_8): BOOLEAN
			-- Is a_byte the first byte in UTF-8 encoding?
		ensure
			instance_free: class

	is_encoded_next_byte (a_byte: CHARACTER_8): BOOLEAN
			-- Is a_byte one of the next bytes in UTF-8 encoding?
		ensure
			instance_free: class

	is_encoded_second_byte (a_byte, a_first_byte: CHARACTER_8): BOOLEAN
			-- Is a_byte a valid second byte in UTF-8 encoding?
		require
			valid_first_byte: is_encoded_first_byte (a_first_byte)
		ensure
			instance_free: class

	is_endian_detection_character (a_first, a_second, a_third: CHARACTER_8): BOOLEAN
			-- Is this sequence a UTF-8 Byte Order Marker (BOM)?
		ensure
			instance_free: class
			result_start: Result implies is_endian_detection_character_start (a_first, a_second)

	is_endian_detection_character_start (a_first, a_second: CHARACTER_8): BOOLEAN
			-- Are these characters the start of a UTF-8 encoded Byte Order Marker (BOM)?
		ensure
			instance_free: class

	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
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))

	valid_utf8 (a_string: STRING_8): BOOLEAN
			-- Are the bytes in a_string a valid UTF-8 encoding?
		require
			a_string_not_void: a_string /= Void
			a_string_is_string: Any_.same_types (a_string, "")
		ensure
			instance_free: class
	
feature -- Element change

	append_code_to_utf8 (a_utf8: STRING_8; a_code: INTEGER_32)
			-- Add UTF-8 encoded character of code a_code
			-- at the end of a_utf8.
		require
			a_utf8_not_void: a_utf8 /= Void
			a_utf8_is_string: Any_.same_types (a_utf8, "")
			a_utf8_valid: valid_utf8 (a_utf8)
			valid_code: Unicode.valid_non_surrogate_code (a_code)
		ensure
			instance_free: class
			a_utf8_valid: valid_utf8 (a_utf8)
	
feature -- Conversion

	to_utf8 (a_string: STRING_8): STRING_8
			-- New STRING made up of bytes corresponding to
			-- the UTF-8 representation of a_string
		require
			a_string_not_void: a_string /= Void
		ensure
			instance_free: class
			to_utf8_not_void: Result /= Void
			string_type: Any_.same_types (Result, "")
			valid_utf8: valid_utf8 (Result)
	
feature -- Duplication

	copy (other: UC_UTF8_ROUTINES)
			-- 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)
		ensure -- from ANY
			is_equal: Current ~ other

	frozen deep_copy (other: UC_UTF8_ROUTINES)
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)

	frozen deep_twin: UC_UTF8_ROUTINES
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)

	frozen standard_copy (other: UC_UTF8_ROUTINES)
			-- 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)
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)

	frozen standard_twin: UC_UTF8_ROUTINES
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)

	frozen twin: UC_UTF8_ROUTINES
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
	
feature -- Basic operations

	frozen default: detachable UC_UTF8_ROUTINES
			-- Default value of object's type
			-- (from ANY)

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

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

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
	
feature -- Output

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void

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

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		ensure -- from ANY
			instance_free: class

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

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
	
invariant
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

end -- class UC_UTF8_ROUTINES

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