PostScript binary object format - Revision history

Zzo38 at 02:24, 28 August 2021

2021-08-28T02:24:31Z

Zzo38 at 02:17, 28 August 2021

2021-08-28T02:17:32Z

Zzo38: The nonstandard capability to encode dictionaries in the PostScript binary object format has recently been removed from Ghostscript.

2020-08-24T23:28:15Z

The nonstandard capability to encode dictionaries in the PostScript binary object format has recently been removed from Ghostscript.

Zzo38 at 21:31, 8 March 2020

2020-03-08T21:31:21Z

Zzo38: Created page with "{{FormatInfo |formattype=electronic |subcat=Serialization |extensions={{ext|ps}} }} PostScript binary object format is a binary format for serialization of data structure..."

2020-03-08T20:54:28Z

Created page with "{{FormatInfo |formattype=electronic |subcat=Serialization |extensions={{ext|ps}} }} PostScript binary object format is a binary format for serialization of data structure..."

New page

{{FormatInfo
|formattype=electronic
|subcat=Serialization
|extensions={{ext|ps}}
}}

PostScript binary object format is a binary format for [[serialization]] of data structures, and it is produced by the <tt>printobject</tt> and <tt>writeobject</tt> operators in [[PostScript]], and can also be read by PostScript.

The first byte is always in range 128 to 131, which indicates [[endianness]] and floating point format, where 128 means big-endian integers with native floating numbers, 129 means small-endian integers with native floating numbers, 130 means big-endian integers with big-endian IEEE floating numbers, and 131 means small-endian integers with small-endian IEEE floating numbers. However, due to a bug in Adobe's software (this bug is also emulated in Ghostscript for compatibility), 128 and 129 actually act like 130 and 131 if the native floating point format is IEEE.

After that is the rest of the header, which can be either a short or long header:
* Short header: 8-bit number of objects in top-level array (which must be nonzero), followed by 16-bit overall length in bytes (including the header).
* Long header: Zero (one byte), followed by 16-bit number of objects in top-level array, followed by 32-bit overall length in bytes (including the header).

@@ Line 65: / Line 65: @@
 #define obj_index(x,y) (obj_rawvalue(x)+(y)*8)
 #define obj_int(x) ({ int x__=(x); int t_=obj_type(x__); t_==TY_INT||t_==TY_BOOL?obj_rawvalue(x__):t_==TY_REAL?(int)obj_ufloat(x__):0; })
 #define obj_isnum(x) ({ int x__=(x); obj_type(x__)==TY_INT || obj_type(x__)==TY_REAL; })
 #define obj_length(x) ({ int x__=(x); (object[x__+2]<<8)|object[x__+3]; })

← Older revision		Revision as of 02:17, 28 August 2021
Line 46:		Line 46:
	For floating numbers, the scale factor is normally zero; this means the value is encoded as a floating number in the IEEE or native format (according to the header). If written out by PostScript, this is always the case. Nonzero scale factors means it is encoded as an integer, and the scale factor is the number of fraction bits. The use of nonzero scale factors is not recommended for interchange, since PostScript doesn't write them out, and the implementation in other programming languages can be simplified if they are not used.		For floating numbers, the scale factor is normally zero; this means the value is encoded as a floating number in the IEEE or native format (according to the header). If written out by PostScript, this is always the case. Nonzero scale factors means it is encoded as an integer, and the scale factor is the number of fraction bits. The use of nonzero scale factors is not recommended for interchange, since PostScript doesn't write them out, and the implementation in other programming languages can be simplified if they are not used.

−	The ability to store dictionaries in PostScript binary object format is a nonstandard extension which is implemented in Ghostscript (although it is disabled by default, and has recently been removed). It is encoded like an array, with alternating keys and values. The keys must all be distinct, and keys may not be nulls or strings.	+	The ability to store dictionaries in PostScript binary object format is a nonstandard extension which was implemented in Ghostscript (although it is disabled by default, and has recently been removed). It is encoded like an array, with alternating keys and values. The keys must all be distinct, and keys may not be nulls or strings.
		+
		+	== Implementation in C ==
		+
		+	The following implementation in C is public domain. This implementation is only reading the data, and does not do writing. The variable called <tt>object</tt> is expected to point to the type byte of the first object, and the data is expected to be in big-endian format.
		+
		+	<pre>
		+	#define TY_NULL 0
		+	#define TY_INT 1
		+	#define TY_REAL 2
		+	#define TY_NAME 3
		+	#define TY_BOOL 4
		+	#define TY_STRING 5
		+	#define TY_ARRAY 9
		+	#define TY_MARK 10
		+
		+	#define obj_float(x) ({ int x__=(x); int t_=obj_type(x__); t_==TY_INT?(float)obj_rawvalue(x__):t_==TY_REAL?obj_ufloat(x__):0; })
		+	#define obj_index(x,y) (obj_rawvalue(x)+(y)*8)
		+	#define obj_int(x) ({ int x__=(x); int t_=obj_type(x__); t_==TY_INT\|\|t_==TY_BOOL?obj_rawvalue(x__):t_==TY_REAL?(int)obj_ufloat(x__):0; })
		+	#define obj_int64(x) ({ int x__=(x); int t_=obj_type(x__); t_==TY_INT\|\|t_==TY_BOOL?obj_rawvalue(x__):t_==TY_REAL?(sqlite3_int64)obj_ufloat(x__):0; })
		+	#define obj_isnum(x) ({ int x__=(x); obj_type(x__)==TY_INT \|\| obj_type(x__)==TY_REAL; })
		+	#define obj_length(x) ({ int x__=(x); (object[x__+2]<<8)\|object[x__+3]; })
		+	#define obj_ptr(x) (object+obj_rawvalue(x))
		+	#define obj_rawvalue(x) ({ int y__=(x); (int)((object[y__+4]<<24)\|(object[y__+5]<<16)\|(object[y__+6]<<8)\|object[y__+7]); })
		+	#define obj_tag() (object[1])
		+	#define obj_type(x) (object[x]&127)
		+	#define obj_ufloat(x) ({ union { int i; float f; } f__; f__.i=obj_rawvalue(x); f__.f; }) // see psi/ibnum.h in Ghostscript for an explanation of this bug
		+	</pre>

← Older revision		Revision as of 23:28, 24 August 2020
Line 46:		Line 46:
	For floating numbers, the scale factor is normally zero; this means the value is encoded as a floating number in the IEEE or native format (according to the header). If written out by PostScript, this is always the case. Nonzero scale factors means it is encoded as an integer, and the scale factor is the number of fraction bits. The use of nonzero scale factors is not recommended for interchange, since PostScript doesn't write them out, and the implementation in other programming languages can be simplified if they are not used.		For floating numbers, the scale factor is normally zero; this means the value is encoded as a floating number in the IEEE or native format (according to the header). If written out by PostScript, this is always the case. Nonzero scale factors means it is encoded as an integer, and the scale factor is the number of fraction bits. The use of nonzero scale factors is not recommended for interchange, since PostScript doesn't write them out, and the implementation in other programming languages can be simplified if they are not used.

−	The ability to store dictionaries in PostScript binary object format is a nonstandard extension which is implemented in Ghostscript (although it is disabled by default). It is encoded like an array, with alternating keys and values. The keys must all be distinct, and keys may not be nulls or strings.	+	The ability to store dictionaries in PostScript binary object format is a nonstandard extension which is implemented in Ghostscript (although it is disabled by default, and has recently been removed). It is encoded like an array, with alternating keys and values. The keys must all be distinct, and keys may not be nulls or strings.

@@ Line 6: / Line 6: @@
 PostScript binary object format is a binary format for [[serialization]] of data structures, and it is produced by the <tt>printobject</tt> and <tt>writeobject</tt> operators in [[PostScript]], and can also be read by PostScript.
 The first byte is always in range 128 to 131, which indicates [[endianness]] and floating point format, where 128 means big-endian integers with native floating numbers, 129 means small-endian integers with native floating numbers, 130 means big-endian integers with big-endian IEEE floating numbers, and 131 means small-endian integers with small-endian IEEE floating numbers. However, due to a bug in Adobe's software (this bug is also emulated in Ghostscript for compatibility), 128 and 129 actually act like 130 and 131 if the native floating point format is IEEE.
@@ Line 12: / Line 14: @@
 * Short header: 8-bit number of objects in top-level array (which must be nonzero), followed by 16-bit overall length in bytes (including the header).
 * Long header: Zero (one byte), followed by 16-bit number of objects in top-level array, followed by 32-bit overall length in bytes (including the header).