String Type
Hello All,
The following is my design for a string type. I would prefer if it were
directly implemented by the compiler but it could be implemented by
libraries. As will undoubtablely be pointed out it is usually faster to read
a word (literal meaning) but the space saved in memmory plus all the
advantages to speed of having a restricted type would make it far out way
the advantages of reading a word. That and it would have less time and space
overhead of a sequence.
String Library Design.
======================
Author : Mathew Hounsell
Purpose : To provide a library capable of providing string functions
to Euphoria.
Reason For Use Over Internal Types : The sequence use four bytes per
character, wasting three.
Goals : * Minimum storage per string.
- 1 byte per character.
- + x Bytes overhead.
* Euphoria style internl handling.
- Reference Counts.
- Stored Length.
* Variablle length.
Other Considerations : Four byte boundaries.
Data Structure Design : Length.
Reference Count.
String...
The length of a string should be variable. However the greater the maximum
size the greater the over head. Therefore a size of a reasonable length
is needed. If one byte is used the string is limited to 256 bytes,
often too small. If two bytes are used the string length is 64Kb which
should in most cases be adequate.
A maximum number for the refence count needs to be decided. One byte (256)
should be adequate.
Since Euphoria &/ OS will allocate memmory on four byte boundaries and of
an
actual length of a multiple of 4 then we will do the same and use the
extra space if needed. Since the padding is to make the size a
muultiple
of four it will be a maximum of 3 bytes.
Data Structure Re-Design : Length (2B).
Reference Count (1B)
Size of Padding (2bits-1B)
String... ( < 64K )
Padding... ( < 3B )
User Interaction : Will be based on a virtual address, the start of the
string after the overhead.
Actions : - Creation
- Deletion
- Determining Length
- Duplication
- Replacing
- Getting a Character
- Changing a Character
- Finding a Character
- Comparing
- Outputing
- Concaternating a String and a Character
- Concaternating two Strings
- Make a String Upper Case
- Make a String Lower Case
- Transforming to a C String
- Transforming to a Euphoria Sequence
- Transforming from a C String
- Transforming from a Euphoria Sequence
- Slicing
- Matching a Partial String
- Inputing
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INTERNAL TYPE VVA : a <-- Valid Virtual Adrress
IF a THEN
RETURN OK
ENDIF
ERROR : "String Does Not Exist"
RETURN NOT_OK
END TYPE
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SUB Create : Length
determine needed memmory including over head
determine amount of padding
allocate total needed memmory
IF the memmory was allocated THEN
store the Length
store 0 for the refernce count
store the ammount of padding
RETURN the virtual address
END IF
RETURN 0
END SUB
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SUB Delete : Address
IF refernce count > 1 THEN
decrement reference count
ELSE
free the memmory
END IF
END SUB
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SUB Length : VVA Address
RETURN string length
END SUB
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INTERNAL SUB copy_str : VVA Address
NewAddress = ( Create: ( Length:Address ) )
IF NewAddress THEN
copy contents of string into new string
END IF
RETURN NewAddress
END IF
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SUB Duplicate : VVA Address
IF refence count < max THEN
increment reference count
RETURN Address
END IF
RETURN ( copy_str:Address )
END SUB
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SUB Replace : VVA Destenation, VVA Source
Delete:Destenation
RETURN ( Duplicate:Source )
END IF
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SUB Get_Char : VVA Address, INT Index
IF Index >= 1 AND Index <= ( Length:Address ) THEN
RETURN Address[Index]
END IF
ERROR : "Invalid Index"
END SUB
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SUB Set_Char : VVA Addres, INT Index, CHAR c
IF Index >= 1 AND Index <= ( Length:Address ) THEN
IF Address's refence count > 1 THEN
decrement Address's refernce count
NewAddress = ( copy_str : Address )
IF NewAddress THEN
NewAddress[Index] = c
END IF
RETURN NewAddress
END IF
Address[Index] = c
RETURN Address
END IF
ERROR : "Invalid Index"
END SUB
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SUB Find_Char : VVA Address, CHAR c
FOR i = 1 TO ( Length : Address ) DO
IF Address[i] = c THEN
RETURN i
END IF
END FOR
RETURN 0
END SUB
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SUB Compare : VVA One : VVA Two
FOR i = 1 TO ( Smaller: ( Length:One ),( Length:Two ) ) DO
IF One[i] < Two[i] THEN
RETURN -1
ELSIF One[i] > Two[i] THEN
RETURN 1
END IF
END FOR
RETURN 0
END SUB
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SUB Output : FileNum FN, VVA Address
PUTS : FN, contents of string
END SUB
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SUB ConCat_Char : VVA Address, CHAR c
IF reference count > 1 THEN
IF NOT padding THEN
NewAddress = ( Create: ( Length:Address )+1 )
ELSE
NewAddress = ( Create: ( Length:Address ) )
END IF
IF NOT NewAddress THEN
RETURN 0
END IF
copy contents of string into new string
Delete:Address
Address = NewAddress
END IF
IF padding THEN
decrement Address's padding
END IF
Address[ (Length:Address)+1 ] = c
END SUB
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SUB ConCat_String : VVA Address, VVA Add
NewAddress = ( Create: ( Length:Address)+(Length:Add ) )
IF NOT NewAddress THEN
RETURN 0
END IF
copy contents of Address into new string
copy contents of Add into new string after contents of Address
Delete:Address
END SUB
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SUB To_Upper_Str : VVA Address
IF Address's refence count > 1 THEN
decrement Address's refernce count
NewAddress = ( copy_str : Address )
IF not NewAddress THEN
RETURN NewAddress
END IF
Address = NewAddress
END IF
ITERATE i IN string
Address[i] = upper case Address[i]
END ITERATE
END SUB
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SUB To_Lower_Str : VVA Address
IF Address's refence count > 1 THEN
decrement Address's refernce count
NewAddress = ( copy_str : Address )
IF not NewAddress THEN
RETURN NewAddress
END IF
Address = NewAddress
END IF
ITERATE i IN string
Address[i] = lower case Address[i]
END ITERATE
END SUB
--------------------
Sincerely,
Mathew Hounsell
Mat.Hounsell at Excite.Com
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