11.6.4 BZR postamble

The postamble of a BZR file consists of the following. See section 11.6.1 BZR format introduction, for general information about BZR files and for the definition of the types used here.

POST @cmindex POST opcode in BZR files llx[3] lly[3] urx[3] ury[3] character locators (see below) POST_POST @cmindex POST_POST opcode in BZR files nchars[1] post-ptr[4] id[1] 1 to any number of NO_OP's

Here is a description of these components:

• llx ... ury are all designsize-scaled numbers. They define the bounding box for the entire font, which is simply the smallest box that encloses all the characters. See section 11.6.3.1 BZR character beginnings.

• A character locators provides a pointer to the first byte of the corresponding character description, i.e., its BOC. There are two forms of character locators: one abbreviates the common case of the pointer being less than 65536; the other allows for a full four-byte pointer value.

  More precisely, an abbreviated character locator consists of:

  CHAR_LOC_ABBREV charcode[1] pointer[2]

  and a long character locator consists of:

  CHAR_LOC charcode[1] pointer[4]

• nchars is the number of characters defined in the BZR file.

• post-ptr points to the POST byte.

• id identifies the version of BZR format; this is currently 75.

This way of ending BZR files makes it straightforward to process a BZR file from end to beginning, even though it must of course be written beginning to end. The BZR-reading program can position itself at the end of the file, skip over the NO_OP bytes at the end to the id byte, and then read the pointer to the postamble proper, which provides enough information to read each character individually. This eliminates the need to read the entire (potentially large) BZR file into memory before doing any processing.