OS/2 2.0 Information Presentation Facility (IPF) Data Format

by Carl Hauser, Marcus Groeber and Graeme Geldenhuys

Carl Hauser's Introduction
Having become extremely frustrated by VIEW.EXE's penchant for windows that come and go, without even opening large enough to see everything in them, I thought I'd try to turn .INF files into something more conventional. While I don't have code to offer, I can tell you what I learned about .INF format – it was enough to produce more-or-less readable more-or-less plaintext from .INFs.

I offer this in the hope that somebody will give the community a really nice, tasteful, convenient, doesn't-use-too-much-screen-real-estate .INF browser to replace VIEW.EXE.

All of this was developed by looking at .INF files without any documentation of the format except what VIEW.EXE showed for a particular feature.

I don't have a lot of personal interest in refining this document with additional escape sequences, etc., but I would be happy to correspond with someone who wanted to fill in the details, or to clarify anything that may be confusing. If someone could point us to an official document describing the format that would be most helpful.

Marcus Groeber's Introduction
The original document contained most of the real tricky stuff in the file format (especially the compression algorithm) so going on from there was mainly a task of creating lots of help files using the IPFC and the decompiling them again to see what came out.

I fixed a few minor bugs in the description of the header which was extended to describe the entire structure I believe to be the header (because variable data starts afterwards).

A number of escape codes have also been added and the descriptions of others have been refined. There are still a lot of question marks about the format, but this description already allows disassembling the text into ASCII form in a fairly true-to-life format (including indentations etc.).

Further research should go into the way multiple windows are handled (I didn't work on that because I have never required multiple window displays in my help files and therefore am not familiar with the concepts). Font usage and graphics linking could also use some more fiddling around.

Types
All numeric quantities are least-significant-byte first in the file(little-endian).

bit1      1 bit boolean           \  used only for explaining int4      4 bit unsigned integer  /  packed structures char8     8 bit character (ASCII more-or-less) int8      8 bit unsigned integer int16     16 bit unsigned integer int32     32 bit unsigned integer

The File Header
Starting at file offset 0 the following structure can overlay the file to provide some starting values: {         int16 ID;           // ID magic word (5348h = "HS") int8 unknown1;     // unknown purpose, could be third letter of ID          int8  flags;        // probably a flag word... // bit 0: set if INF style file // bit 4: set if HLP style file // patching this byte allows reading HLP files // using the VIEW command, while help files // seem to work with INF settings here as well. int16 hdrsize;     // total size of header int16 unknown2;    // unknown purpose int16 ntoc;        // 16 bit number of entries in the tocarray int32 tocstrtablestart; // 32 bit file offset of the start of the // strings for the table-of-contents int32 tocstrlen;   // number of bytes in file occupied by the // table-of-contents strings int32 tocstart;    // 32 bit file offset of the start of tocarray int16 nres;        // number of panels with ressource numbers int32 resstart;    // 32 bit file offset of ressource number table int16 nname;       // number of panels with textual name int32 namestart;   // 32 bit file offset to panel name table int16 nindex;      // number of index entries int32 indexstart;  // 32 bit file offset to index table int32 indexlen;    // size of index table int8 unknown3[10]; // unknown purpose int32 searchstart; // 32 bit file offset of full text search table int32 searchlen;   // size of full text search table int16 nslots;      // number of "slots" int32 slotsstart;  // file offset of the slots array int32 dictlen;     // number of bytes occupied by the "dictionary" int16 ndict;       // number of entries in the dictionary int32 dictstart;   // file offset of the start of the dictionary int32 imgstart;    // file offset of image data int8 unknown4;     // unknown purpose int32 nlsstart;    // 32 bit file offset of NLS table int32 nlslen;      // size of NLS table int32 extstart;    // 32 bit file offset of extended data block int8 unknown5[12]; // unknown purpose char8 title[48];   // ASCII title of database }

The table of contents array
Beginning at file offset tocstart, this structure can overlay the file: {          int32  tocentrystart[ntoc];       // array of file offsets of                                             // tocentries }

The table of contents entries
Beginning at each file offset, tocentrystart[i]: {          int8 len;          // length of the entry including this byte int8 flags;       // flag byte, description folows (MSB first) // bit1 haschildren; // following nodes are a higher level // bit1 hidden;      // this entry doesn't appear in VIEW.EXE's                                 // presentation of the toc // bit1 extended;    // extended entry format // bit1 stuff;       // ?? // int4 level;       // nesting level int8 ntocslots;   // number of "slots" occupied by the text for // this toc entry }

if the "extended" bit is not 1, this is immediately followed by

{          int16 tocslots[ntocslots]; // indices of the slots that make up                                      // the article for this entry char8 title[];            // the remainder of the tocentry // until len bytes have been used [not // zero terminated] }

if extended is 1 there are intervening bytes that (I think) describe the kind, size and position of the window in which to display the article. I haven't decoded these bytes, though in most cases the following tells how many there are. Overlay the following on the next two bytes: {   int8 w1; int8 w2; } Here's a C code fragment for computing the number of bytes to skip: int bytestoskip = 0; if (w1 & 0x8) { bytestoskip += 2 }; if (w1 & 0x1) { bytestoskip += 5 }; if (w1 & 0x2) { bytestoskip += 5 }; if (w2 & 0x4) { bytestoskip += 2 };

skip over bytestoskip bytes (after w2) and find the tocslots and title as in the non-extended case.

The Slots array
Beginning at file offset slotsstart (provided by the file header) find {   int32 slots[nslots];       // file offset of the article // corresponding to this slot }

The Dictionary
Beginning at file offset dictstart (provided by the file header) and continuing until ndict entries have been read (and dictlen bytes have been consumed from the file) find a sequence of length-preceeded strings. Note that the length includes the length byte (not Pascal compatible!). Build a table mapping i to the ith string. {   char8*     strings[ndict]; }

The Article entries
Beginning at file offset slots[i] the following structure can overlay the file: {          int8       stuff;          // ?? [always seen 0] int32     localdictpos;   // file offset of the local dictionary int8      nlocaldict;     // number of entries in the local dict int16     ntext;          // number of bytes in the text int8      text[ntext];    // encoded text of the article }

The Local dictionary
Beginning at file position localdictpos (for each article) there is an array: {     int16      localwords[nlocaldict]; }

The Text
The text for an article then consists of words obtained by referencing strings[localwords[text[i]]] for i in (0..ntext), with the following exceptions. If text[i] is greater than nlocaldict it means

0xfa => end-of-paragraph, sets spacing to TRUE if                not in a monospace example)       0xfb => [unknown]       0xfc => spacing = !spacing       0xfd => line break (outside an example: ".br", sets spacing to TRUE if not in a                monospace example)       0xfe => space       0xff => escape sequence                        // see below

When spacing is true, each word needs a space put after it. When false, the words are abutted and spaces are supplied using 0xfe or the dictionary. Examples are entered and left with 0xff escape sequences. The variable "spacing" is initially (start of every article slot) TRUE.

0xff escape sequences
These are used to change fonts, make cross references, enter and leave examples, etc. The general format is: {   int8       FF;             // always equals 0xff int8      esclen;         // length of the sequence (including                               // esclen but excluding FF) int8      escCode;        // which escape function } escCodes I have partially deciphered are The font used in the text is the normal IBM extended character set, including line graphics and some of the characters below 32.

The ressource number array
Beginning at file offset resstart, this structure can overlay the file: {           int16  res[nres];         // ressource number of panels int16 toc[nres];         // toc entry number of panel }

The text name array
Beginning at file offset namestart, this structure can overlay the file: {           int16  name[nres];        // index to panel name in dictionary int16 toc[nres];         // toc entry number of panel }

The index table
Beginning at file offset indexstart, a structure like the following is stored for each of the nindex words (in alphabetical order). {           int8  nword;              // size of name int8 level;              // indent level // bit 6 set: global entry int8 stuff; int16 toc;               // toc entry number of panel char8 word[nword];       // index word [not zero-terminated] }

The extended data block
Not yet decoded. This block has a size of 64 bytes and contains various pointers to font names, names of externel databases etc.

The full text search table
Not yet decoded. This table is supressed when "/S" is specified on the IPFC command line.

Image data
Beginning at file offset imgstart, this data is a series of compressed OS/2 bitmaps. Each starts with a BITMAPFILEHEADER: {          int16 usType;     // 'bM' for bitmap int32 cbSize;    // total bitmap size including header // BEFORE compression: not correct in this context int16 xHotspot;  // only for icons/pointers, not relevant here? int16 yHotspot; int32 offBits;   // offset to the actual bitmap data bits BITMAPINFOHEADER bmp; // further bitmap data: int32 cbFix;   // length of bitmapinfo header structure (12) // (including this field) int16 cx;      // bitmap width int16 cy;      // bitmap height int16 cPlanes; // num bitplanes - always 1 AFAIK int16 bitCount; // bits per pixel e.g. 4 = 16 colors

RGB palette[ N ]; // 2 ^ bitCount * 3 bytes

bitmapData;      // in a special IPF format: int32 totalLength; // not including this field, but including the next int16 bitmapSize; // total size of memory required // for uncompressed bitmap i.e.                               // bytes per line rounded up to longword (4byte) // x rows // (This info is redundant)

Followed by a series of blocks each up to 64k uncompressed. Blocks: int16 dataLength; // length of data following (including data type field)

int8 dataType;   // 0 = uncompressed 2 = compressed data... Compression is LZW (Lempel Ziv Welch)

}

NLS table
Not yet decoded. This table contains informations specific to the language and codepage the document was prepared in. It seems to contain some bitfields as well that might be used for character classification.

Appendix 1: Some useful translations from IBM Extended ASCII to normal ASCII
One other transformation I had to make was of the character box characters of the IBM extended ASCII set. These characters appear in strings in the dictionary. They are given here in octal together with their translation.

Appendix 2: Style codes for escCode 0x04 and 0x0D
escCode 0x04 implements font changes associated with the :hp# IPF source tag. :hp1 is italic font :hp2 is bold font :hp3 is bold italic font :hp5 is normal underlined font :hp6 is italic underlined font :hp7 is bold underlined font

Tags :hp4, :hp8, and :hp9 introduce different colored text which is encoded in the .inf or .hlp file using escCode 0x0D. On my monitor normal text is dark blue. :hp4 text is light blue :hp8 text is red :hp9 text is magenta