question about name checking code in fselect

reyalp

13878

« on: 05 / August / 2008, 20:54:04 »

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Is there a reason things like

Code: [Select]

           if (selected->name[0] == 'D' && selected->name[1] == 'C' && selected->name[2] == 'I' && selected->name[3] == 'M') {//If selected item is DCIM folder

are used instead of str[n]cmp ?

Also, the extension checks such as

Code: [Select]

           else if (selected->name[9] == 'C' || selected->name[9] == 'T' || selected->name[9] == 'W' || selected->name[9] == 'J') {//If seleted item is a file produced by the camera

just use the 10th letter. Not only will XXXXXXXX.[CTWJ]?? match, name[9] might also be after the end of the name (and off the end off the buffer if I'm not mistaken.)

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DataGhost

314
EOS 40D, S5IS

Re: question about name checking code in fselect

« Reply #1 on: 06 / August / 2008, 05:49:32 »

The DCIM folder layout and naming follows some standard (forgot which one), which states that the files are of the form
AAAAXXXX.EXT
AAAA being four characters, doesn't really matter what
XXXX being four numbers, must be unique unless the files belong to each other (AVI + THM, for example)
EXT being the extension, of course.
So there is really no way that the camera produces a file, in the DCIM folder, which doesn't pass validation in this way. Granted, it's probably not the best way but it works.

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ewavr

1057
A710IS

Re: question about name checking code in fselect

« Reply #2 on: 06 / August / 2008, 06:06:55 »

Quote from: reyalp on 05 / August / 2008, 20:54:04

Is there a reason things like
Code: [Select]
if (selected->name[0] == 'D' && selected->name[1] == 'C' && selected->name[2] == 'I' && selected->name[3] == 'M') {//If selected item is DCIM folderare used instead of str[n]cmp ?

Offtopic on

Maybe, it works faster?

Code: [Select]

  if ((*(long*)selected->name)==0x4D494344)

Works superfast.

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reyalp

13878

Re: question about name checking code in fselect

« Reply #3 on: 06 / August / 2008, 17:32:11 »

@dataghost:
Thanks. It looks like this Design rule for Camera File system - Wikipedia, the free encyclopedia is the standard in question.
Version 1 can be found as a PDF, the latest is about $50 from JEITA

Quote from: ewavr on 06 / August / 2008, 06:06:55

Maybe, it works faster?
Code: [Select]
if ((*(long*)selected->name)==0x4D494344)Works superfast.

When the next operation involves reading/writing flash or updating the most of the display framebuffer anyway, I'd take clarity over a few ns more performance

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