tango.text.convert.Utf

License:

BSD style: see license.txt

Version:

Initial release: Oct 2004

Authors:

Kris

Fast Unicode transcoders. These are particularly sensitive to minor changes on 32bit x86 devices, because the register set of those devices is so small. Beware of subtle changes which might extend the execution-period by as much as 200%. Because of this, three of the six transcoders might read past the end of input by one, two, or three bytes before arresting themselves. Note that support for streaming adds a 15% overhead to the dchar => char conversion, but has little effect on the others.

These routines were tuned on an Intel P4; other devices may work more efficiently with a slightly different approach, though this is likely to be reasonably optimal on AMD x86 CPUs also. These algorithms would benefit significantly from those extra AMD64 registers. On a 3GHz P4, the dchar/char conversions take around 2500ns to process an array of 1000 ASCII elements. Invoking the memory manager doubles that period, and quadruples the time for arrays of 100 elements. Memory allocation can slow down notably in a multi-threaded environment, so avoid that where possible.

Surrogate-pairs are dealt with in a non-optimal fashion when transcoding between utf16 and utf8. Such cases are considered to be boundary-conditions for this module.

There are three common cases where the input may be incomplete, including each 'widening' case of utf8 => utf16, utf8 => utf32, and utf16 => utf32. An edge-case is utf16 => utf8, if surrogate pairs are present. Such cases will throw an exception, unless streaming-mode is enabled ~ in the latter mode, an additional integer is returned indicating how many elements of the input have been consumed. In all cases, a correct slice of the output is returned.

For details on Unicode processing see:
inout(char[]) toString(inout(char[]) src, char[] dst = null, size_t* ate = null)
Symmetric calls for equivalent types; these return the provided input with no conversion
char[] toString(const(wchar[]) input, char[] output = null, size_t* ate = null)
Encode Utf8 up to a maximum of 4 bytes long (five & six byte variations are not supported).
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls. For example: 

1
2
3
4
5
6
7

char[] output;

char[] result = toString (input, output);

// reset output after a realloc
if (result.length > output.length)
    output = result;

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
wchar[] toString16(const(char[]) input, wchar[] output = null, size_t* ate = null)
Decode Utf8 produced by the above toString() method.
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls.

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
char[] toString(const(dchar[]) input, char[] output = null, size_t* ate = null)
Encode Utf8 up to a maximum of 4 bytes long (five & six byte variations are not supported). Throws an exception where the input dchar is greater than 0x10ffff.
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls.

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
dchar[] toString32(const(char[]) input, dchar[] output = null, size_t* ate = null)
Decode Utf8 produced by the above toString() method.
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls.

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
wchar[] toString16(const(dchar[]) input, wchar[] output = null, size_t* ate = null)
Encode Utf16 up to a maximum of 2 bytes long. Throws an exception where the input dchar is greater than 0x10ffff.
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls.

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
dchar[] toString32(const(wchar[]) input, dchar[] output = null, size_t* ate = null)
Decode Utf16 produced by the above toString16() method.
If the output is provided off the stack, it should be large enough to encompass the entire transcoding; failing to do so will cause the output to be moved onto the heap instead.

Returns a slice of the output buffer, corresponding to the converted characters. For optimum performance, the returned buffer should be specified as 'output' on subsequent calls.

Where 'ate' is provided, it will be set to the number of elements consumed from the input, and the output buffer will not be resized (or allocated). This represents a streaming mode, where slices of the input are processed in sequence rather than all at one time (should use 'ate' as an index for slicing into unconsumed input).
dchar decode(const(char[]) src, ref size_t ate)
Decodes a single dchar from the given src text, and indicates how many chars were consumed from src to do so.
dchar decode(const(wchar[]) src, ref size_t ate)
Decodes a single dchar from the given src text, and indicates how many wchars were consumed from src to do so.
char[] encode(char[] dst, dchar c)
Encode a dchar into the provided dst array, and return a slice of it representing the encoding
wchar[] encode(wchar[] dst, dchar c)
Encode a dchar into the provided dst array, and return a slice of it representing the encoding
bool isValid(dchar c)
Is the given character valid?
inout(T[]) fromString8(T)(inout(char[]) s, T[] dst)
Convert from a char[] into the type of the dst provided.
Returns a slice of the given dst, where it is sufficiently large to house the result, or a heap-allocated array otherwise. Returns the original input where no conversion is required.
inout(T[]) fromString16(T)(inout(wchar[]) s, T[] dst)
Convert from a wchar[] into the type of the dst provided.
Returns a slice of the given dst, where it is sufficiently large to house the result, or a heap-allocated array otherwise. Returns the original input where no conversion is required.
inout(T[]) fromString32(T)(inout(dchar[]) s, T[] dst)
Convert from a dchar[] into the type of the dst provided.
Returns a slice of the given dst, where it is sufficiently large to house the result, or a heap-allocated array otherwise. Returns the original input where no conversion is required.
T[] cropLeft(T)(T[] s)
Adjust the content such that no partial encodings exist on the left side of the provided text.
Returns a slice of the input
T[] cropRight(T)(T[] s)
Adjust the content such that no partial encodings exist on the right side of the provided text.
Returns a slice of the input