Mistakes in books: Sedoric à Nu

Here is the place to discuss about the magazines (CEO Mag, OUM, Rhetoric, Theoric, Hebdogiciel, ... are all welcome here) and books.
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Symoon
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Mistakes in books: Sedoric à Nu

Post by Symoon » Fri Dec 04, 2015 10:52 pm

Page 207, address D503, André wonders if there's not a bug as a JSR D7BD seems to be repeated very closely.
It is also listed as an uncorrected bug page 571.

This is not a bug.
Actually, the code here is trying to validate the drive letter asked by the user. But there are two ways to ask for a drive:
1- entering "A-" (or B- or C- or D- ) will set the default drive to the chosen letter. Any file load attempt will be made from this default drive
2- loading a file specifying the drive where it's stored, therefore bypassing the default drive, for instance: LOAD"B-ZAKMCKRAK" will load the file ZAKMCKRAK on the drive B, whatever the default drive is (and providing Chema has ported the game ;))

So the two JSR D7BD are there for these two ways of asking for a drive: one will just be used to load a file, the other will set the default drive. They are two different entries, each one requiring (more or less, but that's another story) the JSR D7BD.
Last edited by Symoon on Fri Dec 04, 2015 11:15 pm, edited 1 time in total.

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Re: Mistakes in books: Sedoric à Nu

Post by Symoon » Fri Dec 04, 2015 11:12 pm

Page 497, is written:
octet 0F attribut de protection (b6=1, PROT si b7=1, UNPROT si b7=0)
(#40 = 0100 0000 pour UNPROT et #C0 = 1100 0000 pour PROT). b0 à b5 = HH du nombre de secteurs = rarement utilisés, sauf pour les très gros fichiers mergés.
In other words, the book explains that in a file catalog entry, bits 0 to 5 of a dedicated byte are the most significant bits of a file size (in occupied sectors). So displaying this size would use 8 bits + bits 0 to 5 = up to 14 bits.

This seems unlikely, it should rather be bits 0 to 3 (so 12 bits), leading to a maximum size of 4096 sectors, which is 1MB. Don't think any disk would hold such a big file!
Also, page 278, address #E331, is an AND#0F (mask 00001111), proof that only 4 bits are used.
This has also been tested by setting the 5th bit to 1: DIR doesn't show any file size change, but altering the 3rd bit instead affects the displayed size indeed.

So actually, bit 4 and bit 5 were unused. Bit 5 is now dedicated to flag a directory (in the Sedoric directories demo).
(This mistake was explained in the CEO-Magazine looong ago)

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Re: Mistakes in books: Sedoric à Nu

Post by Godzil » Sun Dec 06, 2015 11:39 pm

Thanks Symoon for that errata :)

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