flat assembler - FASMLIB - text to binary routines design

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vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 25 Oct 2006, 22:47

i am designing routine that reads number from text, and returns it as binary number.

question is: how to beheave if we are NOT on number. I can either return ZF=1, or return standard FASM error.

advantage of ZF-way is, that if caller wants to handle this, it's simple conditional jump agains complicated construct

disadvantage of ZF-way is, that caller always has to care about catching this case.

advantage of error is, that even if caller doesn't handle this case, he still ends up with "Awaing numeric value" error.

disadvantage is, that if caller wants to handle error (eg. provide info about line and column where the error happened), he has to create complicated construct.

Example:

With ZF way:

Code:

libcall text.read.hex2b, stdin
jc .error
jz .error_awaiting_number ;ZF set when we are NOT on number
;EAX = number here
...
...
.error_awaiting_number:
;print line and columnt number, name of document, etc. 
;this can be common for entire text reading

but if i decide this way, you ALWAYS need to have "jz" or "jnz" after every such routine.

With error way, this is the lazy option:

Code:

libcall text.read.hex2b, stdin
jc .error
;EAX = number here

eg. if we don't care about much output, we just leave it this way and user gets at least "Awaiting numeric value".
If we want to handle error with this way, it's possible, but with more effort:

Code:

libcall text.read.hex2b, stdin
jnc @f
cmp eax, ERR_NOT_NUMERIC
je .error_awaiting_number
jmp .error
@@:

Code:

libcall text.read.hex2b, stdin
jc .error_readnum
...
.error_readnum:  ;common for all number reading calls
cmp eax, ERR_NOT_NUMERIC
je .error_awaiting_numer
jmp .error

soooo

25 Oct 2006, 22:47

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 25 Oct 2006, 22:50

by the way, i am doing same with EOF (end of file) and OF flag. But in that case i HAVE to do it through flag, so no questioning there

25 Oct 2006, 22:50

dead_body

Joined: 21 Sep 2005
Posts: 187
Location: Ukraine,Kharkov

dead_body 26 Oct 2006, 04:19

i am for the flag.

26 Oct 2006, 04:19

shoorick

Joined: 25 Feb 2005
Posts: 1614
Location: Ukraine

shoorick 26 Oct 2006, 05:27

a2f function i had wrote returns eax=0&ZF=1 on error, otherwise number in ST0 and pointer to the first byte after loaded number, so you can check is it valid terminator (like zero, space, tab or any other for specific situation)

26 Oct 2006, 05:27

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 26 Oct 2006, 10:14

shoorick: i provided too few info. FASMLIB functions always return error wth CF=1/EAX=error code. my conversion routines beheave similar to what you described (except number is returned in EAX, and conversion length is stored in variable pointed by function argument).

But this operation is working with stream, eg. after you read number, next read (or peek) from stream shows you terminator character.

This is not issue, problem is whether to use flag (faster for lowlevel typing, less standardized) or return standard error (needs uglier code constructs, but is very "general").

I also forgot to mention one PRO of error: in future, it will be possible to very easily implement mass catching of errors, like in HLLs:

Code:

try
  libcall text.read
  libcall text.read
  libcall text.read
  ...
catch ERR_NOT_NUMERIC
  ;print position in text and error here
endtry

i am not personally fan of try-catch, it forces you to write somewhat dumber than with "manual" handling of each call. But still it's nice, and someone might be interested.

so this question can be understood as higher-level vs. low-level

26 Oct 2006, 10:14

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