[Cfp-interest 1731] Re: AI about macro for array size in example

[Mike Cowlishaw]

Definitely go with precedent.   Name the constant as you feel is best.
 
Mike


  _____  

From: Jim Thomas [mailto:jaswthomas at sbcglobal.net] 
Sent: 28 July 2020 18:57
To: Mike Cowlishaw
Cc: CFP
Subject: Re: [Cfp-interest 1718] AI about macro for array size in example


I’ve used the LEN+1 style in code too. But don’t see it anywhere in the C
examples. I’m inclined to stay with my last suggestion, with #define MAXSIZE
41. The text below the code acknowledges the NULL character in the
determination of the size 41. 

- Jim Thomas



On Jul 26, 2020, at 9:49 AM, Mike Cowlishaw <mfc at speleotrove.com> wrote:

Yes, tricky.   STRLEN is one less that the needed constant, too.   In fact,
in my code, I actually use:
  
  #define INTLEN 11           // length needed for an ASCII'd Int    
                              // this is from a shared .h; Int is 32-bit int
.. I never
                              // never use raw 'int' in my code and in fact
in that .h have:  
                              //   #define Int int32_t
                              //   #define int ?
                              // to ensure that I don't [I still have a lot
of 8-bit and 16-bit 
                              // code/platforms to test on]
 
  // then ...
  char buffer[INTLEN+1];      // i.e., the space for the null char is added
here so is explicit
 
So, perhaps
 
   #define MAXHEXCHARS 40
     ...
   char s[MAXHEXCHARS+1];
 
... but maybe we're spending too much time on this :-).  Your call.
 
 


  _____  

From: Jim Thomas [mailto:jaswthomas at sbcglobal.net] 
Sent: 25 July 2020 23:18
To: Mike Cowlishaw
Cc: CFP
Subject: Re: [Cfp-interest 1718] AI about macro for array size in example


I’d like to avoid alluding to the size of a string. It’s really a size
greater than the lengths of the hex strings, which is what is needed for the
array size. The C standard uses “maxsize” for parameters with this meaning.
How about  

#define MAXSIZE 41 // > intermediate hex string length

- Jim Thomas



On Jul 24, 2020, at 6:36 AM, Mike Cowlishaw <mfc at speleotrove.com> wrote:

Looks good.   Maybe MAXSTRSIZE?  (S on its own is a bit mysterious, and it's
not clear how to pronounce it).
 
Mike



  _____  

From: Cfp-interest [mailto:cfp-interest-bounces at oakapple.net] On Behalf Of
Jim Thomas
Sent: 24 July 2020 00:33
To: CFP
Subject: [Cfp-interest 1718] AI about macro for array size in example


Action item:

    Jim: For cfp3x-annex-20200706.pdf, Annex X, new example (page 33),
change the magic number 40 (which needs to be verified) to be a macro and
add in a descriptive definition of that macro.

Oops. 41 instead of 40. How does the following look?

- Jim Thomas

+++++++++++++++++++++++++++
[4] EXAMPLE    If the IEC 60559 binary128 format is supported as a
non-arithmetic format, data in binary128 format can be converted to type
_Decimal128 as follows:

#define __STDC_WANT_IEC_60559_TYPES_EXT__

#include <stdlib.h>

#define MAXSSIZE 41     // of intermediate hexadecimal string 

unsigned char b128[16]; // for input binary128 datum

_Decimal128 d128;       // for result

char s[MAXSSIZE];

// store input binary128 datum in array b128

...

strfromencf128(s, MAXSSIZE, “%a”, b128);

d128 = strtod128(s, NULL);

...

Use of “%a” for formatting assures an exact conversion of the value in
binary format to character sequence. The value of that character sequence
will be correctly rounded to _Decimal128, as specified above in this
subclause. The array s for the output of strfromencf128 need have no greater
size than 41, which is the maximum length of strings of the form

[-]0xh.h
hp±d, where there are up to 29 hexadecimal digits h and d has 5
digits

plus 1 for the null character.

+++++++++++++++++++++++++++














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