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SAR$–Symbolic Access Routines
16.2. SAR$ Internal Format
All of the SDF images handled by the SAR$ functions are placed in internal format.
Internal format provides a common means of handling SDF images in different formats
(nonshift coded, shift-coded, ACD, and so forth). The READ, ATREAD, and COM
functions of SAR$ return SDF images to the calling program in internal format.
The calling program must supply images that will be written out by the WRITE, ATREAD,
and COM functions of SAR$ in internal format.
Internal format consists of the character part and the attribute part.
The character part contains a sequential list of the actual characters contained in the
image. The character part contains no shift codes, attributes, or other special
information. The characters in the character part must be in the ASCII/ISO, ASCII-like, or
JIS-16 (kanji) character sets.
The attribute part contains the attributes that apply to the characters in the character
part. Each attribute is represented as a one-word entry in the attribute table, with the
format in Figure 16–1
index type value
0 17 18 26 27 35
Figure 16–1. SAR$: Attribute Table Entry
The index is an 18-bit integer that indicates the position of the character in the character
part to which this attribute applies. When reading and writing ACD images, the index
range begins with 1 and ends with n, where n is the last 9-bit byte in the character part.
(An index is in 9-bit byte granularity.) When reading and writing shift coded images, the
index range begins with 1 and ends with n + 1. In this case, an index value of n + 1
corresponds to a shift coded image that ends with a shift code and is not followed by
any additional characters. More than one attribute can have the same index. However,
indexes must be in nondecreasing order.
The type is a 9-bit octal value that describes the type of the attribute. The types that are
currently defined are as follows:
001 Reset all attributes to default values
002 The character set type
003 The width of the character
004 The height of the character
005 The horizontal spacing between characters (center to center)
Any number of attributes may apply to the same character.
The value is a 9-bit octal value that provides specific information for the attribute type.
These values are defined in the PLUS COPY element, ACD$VALUES. Table 16-1 lists
the possible values for attribute types.
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